Evolutionary Fixed Potential Agronomic Traits in Polysomic Polyploidy Plants with Special Reference to Potato

It is commonly known that polyploidization has become one of major forces for a speciation and evolution, especially with evolutionary fixed potential agronomic traits in plants. Although several studies demonstrate that allopolyploid plants were successful in developing novel crops, autopolyploid ones are also more substantial and worth exploring. Obviously, autopolyploid development via sexual or asexual pathways can lead to advantages in biomass, changing process of development, and lots of benefits on coping with climate changes do not comprehend as a whole. This review shed light on 1) gaining gigantic effect and increasing phytochemical content; 2) enhancing biotic and abiotic tolerance to adapt to climate change; 3) changing in process of development; 4) adapting ecology. Based on these benefits, this review provides breeders with several choices when they need in the breeding strategies. Also further review on prospects of polyploidy potato in food security is concerned.

• Polyploidisation
• Evolution
• Agronomic Trait
• Potato

1. Introduction

To start with, polyploidy is really vital for human beings mainly because it can open doors of opportunities for success in gaining newly potential crops. Over a century from finding an event that had a set of doubled chromosomes in some plants which was suggested as a polyploid hypothesis by Wing 1917, polyploids have actually undergone an ample history and numerous approaches [1] [2] . Based on origin of parental chromosome resulting polyploidization, two types of polyploids could be classified, namely, paleopolyploids and neopolyploids. Paleo-polyploid flora originated from polyploidy progenitor evolved and went through the milestones of genome doubling, but they existed as diploid due to its re-diploidization via reorganization of various chromosomal sets derived from their ancestors. Neopolyploid plants owned numerous sets of chromosomes which occurred on the periodic polyploidization after combining the parental chromosomes existing independence of each other [3] . According to homologous genomes originated from progenitors, polyploidy plants are also divided into allopolyploid and autopolyploid. With regard to the former, it is combined from parents being different species which forms heterozygous genomes. Autotetraploid results in the same genetic background of their parents having homogenous genomes [4] . Polyploidization was formed by either sexual pathway or somatic chromosome doubling. Concerning the first pathway, the form comprising of the somatic number of chromosomes in diploid pollen and eggs created in meiosis barring the gametophytic number was so-called unreduced gametes or 2n gametes to make polyploidy progenitors and the basic component was for polyploidy development in flora. While, a somatic chromosome doubling was established as chromosomal doubling in somatic cells through mitosis pathway [5] [6] .

With polyploidisation in plant species becoming more prevalent and recurrent than ever, as well as being one of the most essential evolutionary phenomena, resulting in extensively investigating the research field is concerned. Moreover, polyploidy plants become such attention, several favorable agronomic traits are observed that refer to large organ size, vigor, lasting flowers period etc. [7] . When polyploidization occurred, several changes affected by allele dosage related to gene expression and regulation would lead to sequence elimination, methylation, transposon activation, up- and downregulation, subfunctionalisation and neofuctionalisation to form potential agronomic traits [8] [9] . Regarding the former, loss and gain DNA sequences occurred in autotetraploid C. lavandulifolium, A. thaliana, B. rapa [10] [11] [12] [13] and changed in polymorphism at difference of generation of Phlox drummondii Hooker [14] ; gene interaction in A. arenosa [15] . Alteration on gene expression in polysomic polyploid was not high such as Paspalum notatum in 10,000 genes showed 42 homologous genes to 26 divergent genes having function and 22 novel sequences [16] , 4.3% divergent expression in Isatis indigotica [17] , 10% genes changed expression in potato [18] , 6.09% pivotal differential expression in P. fortunei [19] , 2.87% changed level of gene expression in Mulberry (Morus alba L.) [20] , 11.5% of transcriptome and proteome correlation between diploid and tetraploid P. tomentosa [21] , 17% differential gene expression in Tolmiea (Saxifragaceae) [22] , 2677 unigenes were significantly divergently expressed in tetraploid P. tomentosa [23] , 22 genes that happened alternative splicing, showing abilities of making the difference of isoforms of protein in watermelon [24] . Methylation occurred in polysomic polyploid in rice, Malus × domestica Borkh, B. rapa [13] [25] [26] . Translocation appeared in rice and methylated class II of transposable elements shown in A. thaliana [27] [28] . Change in miRNA in C. nankingense [29] [30] . Neofunctionalization was discovered in autotetraploid [16] [31] [32] [33] [34] . Subfunctionalization which is couples of genes exercise a subset of their original genetic functions revealed in maize, Arabidopsis [35] [36] [37] . Autotetraploid Lycopersicon esculentum changed the level of gene expression of the gene dosage such as malate dehydrogenase, acid invertase, glutamate dehydrogenase, and nitrate reductase [38] . Cis-regulatory elements showed extensive difference in regulatory elements and networks in ploidy Arabidopsis. Further, after polyploidisation, dominance effects of allele interaction can occur and be heritable [39] . Another way to contribute to elite polyploidy rice is concerned, heterosis analysis and molecular regulation support long rice panicles [40] . The resurgence of interest in polyploid in recent decades has changed the previous hypothesis which was evolutionary dead-ends in polysomic polyploids by major players in evolution [41] is pointed in Figure 1. This work provides insight into the features of naturally typed and resynthesized polysomic polyploid plants aimed to study evolutionary fixed potential agronomic traits including in extending size of organs and gaining more phytocompounds; reducing the effects of climate change by increasing biotic and abiotic tolerance; altering the developmental process; and widening environmental living and having been typically summarized in Table 1, with special references in potato.

2. Gigantic Effects and Enhance Phytochemical

That polysomic polyploidy outrank diploid one in terms of organ size and biomass typically asserts that up-regulation of genes related to cell division and cell expansion such as ARGOS, ANT (AITEGUMENTA), CYCD3;1, Growth Regulating Factor 1 (AtGRF1) and EXPASIN 10 (AtEXPA10) [42] [43] [44] , EXPB3

Table 1

Some polysomic polyploidy lead to evolutionary fixed potentially agronomic traits

Scientific name	Ploidy	Chromosome	The alternation after polyploidisation	Agronomic traits	Ref.
Lonicera japonica Thunb	Diploid & autotetraploid	2n = 2x = 18, 2n = 4x = 36	Increasing Na+ extrusion in root and supporting Na+ transport to leaf, enhancing photosynthesis	Salt stress	[73]
Oryza sativa Nipponbare	Diploid & autotetraploid	2n = 2x = 24, 2n = 4x = 48	Increasing proline and proton transport; deducing MDA, and Na+ influx into the root	Salt stress	[71]
Brassica rapa L.	Diploid & autotetraploid	2n = 2x = 20 2n = 4x = 40	Up-regulation of antioxidant APX, CAT, POD, SOD, and GR; mitigating ROS	Salt stress	[70]
Paulownia tomentosa	Diploid & autotetraploid	2n = 2x = 40, 2n = 4x = 80	RNA transporter, phytohormone transduction and photosynthesis signal, protein processing, AP2/EREBP, MYB, NAC, and bHLH	Salt stress	[75] [79]
Medicago sativa L.	Diploid & autotetraploid	2n = 2x = 16, 2n = 4x = 32	SNP markers associated to salinity stress, genes functionalized to abiotic stress linked to markers supporting salt tolerance	Salt stress	[76]
Malus domestica	Diploid & autotetraploid	2n = 2x = 34, 2n = 4x = 68	Up-regulation of aquaporin gene (MdPIP1;1 and MdTIP1;1)	Salt stress	[72]
Hordeum bulbosum	Diploid & autotetraploid	2n = 2x = 14, 2n = 4x = 28	miRNAs pitfall salinity stress	Salt stress	[78]
Paulownia fortunei	Diploid & autotetraploid	2n = 2x = 40, 2n = 4x = 80	Rising of soluble sugars, up-regulated ATP synthase to increase ion transport changing proton 8 miRNAs more enhanced and new miRNAs	Salt stress	[74] [77]
P. australis; P. fortunei; P. tomentosa;	Diploid & autotetraploid	2n = 2x = 40, 2n = 4x = 80	miRNAs and target genes associated to transcriptional regulation, hormone metabolism, and plant defense	Drought stress	[81] [82] [83]
Dioscorea zingiberensis	Diploid & autotetraploid	2n = 2x = 20, 2n = 4x = 40	Initiation of the antioxidant defense system and increased heat tolerance	Heat stress	[85]
Nicotiana benthamiana	Tetraploid &octaploid	2n = 4x = 38, 2n = 8x = 76	Rising antioxidant (SOD, CAT, APX...)	Cold stress	[86]
Arabidopsis thaliana	Diploid & autotetraploid	2n = 2x = 10, 2n = 4x = 20	Genes related to Cu transported, AtHMA5, AtCOX17, and AtMT2b, activation of antioxidative defense, positive regulation of expression ABA-responsive genes	Copper stress	[89]
Citrus sinensis L. Poncirustrifoliata L.	Diploid & autotetraploid	2n = 2x = 22, 2n = 4x = 44	Alternation of root anatomical characters	Boron stress	[88]
Betula platyphylla	Diploid & autotetraploid	2n = 2x = 28, 2n = 4x = 56	Up-regulated genes associated to proline biosynthesis	NaHCO3 stress	[90]
Malus × domesticaBorkh	Diploid & autotetraploid	2n = 2x = 34, 2n = 4x = 68	Significantly increased Rvi6 resistance gene-locus	Resistance of Venturia	[91]
Solanum chacoense	Diploid & autotetraploid	2n = 2x = 24, 2n = 4x = 48	Scab resistance originated from Solanum chacoense has introgressed into tetraploid	Scab resistance	[92] [114]
Papaver somniferum L.	Diploid & autotetraploid	2n = 2x = 22, 2n = 4x = 44	Up-regulated alkaloid biosynthesis pathway through gene expression	Increase morphine 25% - 50%.	[56]
Citrullus lanatus	Diploid, autotriploid and autotetraploid	2n = 2x = 22, 2n = 3x = 33, 2n = 4x = 44	Enhancing lycopen biosynthesis pathway via up-regulation genes related	Increase lycopene contents	[58]
Linum album	Diploid and autotetraploid	2n = 2x = 18, 2n = 4x = 36	Increasing the pathway of PTOX biosynthesis by upregulated genes related	Increase podophyllotoxin (PTOX)	[59]

and TCP [45] , the expression of lipid transport genes, wbc11-2 and cer5-2 [46] [47] [48] and by proteins related to cell proliferation, glutathione metabolic pathways and cellulose, chlorophyll, pectin, lignin synthesis [49] [50] . Cytosine methylation genome-wide was as a way to make large body size autotetraploid [51] . Enlarged organ size in polysomic polyploid plants usually leads to increased yield and production crops [52] . These aforementioned benefits, polysomic polyploid enlarged size of plants, but in the case of autotetraploid Birch plant (Betula platyphylla) and apple plants (Malus domestica) were a dwarf morphology that affects by reduced phytohormone cues [53] [54] .

Likewise, polysomic polyploid also increased phytochemical in several plants [55] , the best example of which are those which involve natural compounds such as tetrasomic tetraploid opium poppy (Papaver somniferum L.) enhanced many genes expression related to alkaloid biosynthesis pathway lead to increased morphine content 25% - 50% [56] . Cytosine methylation of genome-wide enhanced phytochemical in autotetraploid Cymbopogon [51] . Investigation on autotetraploids A. thaliana Col-0 showed that metabolites and genes related to TCA (tricarboxylic acid cycle) and GABA (γ-amino butyric acid) changed compare with its diploid [57] . Lycopene in autotriploid watermelons increased due to a regulation of phytohormone on metabolic pathways and upregulation of genes related to biosynthetic lycopene [58] . Autotetraploid Linum album increased concentration of podophyllotoxin (PTOX) caused by upregulated genes related to pathway of PTOX biosynthesis [59] . Autotetraploid Anoectochilus formosanus Hayata produced significantly more contents of total flavonoid and gastrodin [60] . Tetraploid cytotypes of Physalis angutala Linn. from Rajasthan increased palmitic acid, linoleic acid and linolenic acid [61] . In the last century, many plant breeders have given objects based on the outstanding advantages of polyploids. Those breeders have utilized natural and artificial polyploidy as a way to gain elite plant cultivars due to the fact that the increment in plant organs size derived from some of the most significant consequence of polyploidisation [62] .

3. Changing Process of Development

Polyploidy plants offer myriad benefits from enlarged flowers to more extensive the blooming period. A case in point is that whole genome duplication shifted the flowering time and tolerance to new environments in tetraploid Anacamptis pyramidalis [63] . Thus, based on study Brassica rapa (Chinese cabbage) by RNA-seq and sRNA-seq, it was revealed that autotetraploid one prolonged flowering time due to an increase of phyto-hormone levels including the jasmonic acid and indole-3-acetic acid, while a decrease of the abscisic acid as well as regulating of miRNA–target mRNA related to flowering period, petal growth, flowering blooming, and pollen development [64] . After polyploidisation, meiotic stability becomes important because this processing becomes complicated. In studying autotetraploid Arabidopsis lyrata, it is uncovered that novel alleles of ASY1 and ASY3 supported greater stability in the meiotic process [65] [66] . Tetraploid Centaurea phrygia showed greater seed production [67] . Due to gigantic characteristics, autotetraploid rice is not only long and wide grains but also long panicle and seed setting that showed high heterosis and more potential agronomic traits [68] . Based on using CRISPR/cas9 to knout out two genes TMD9-1 and TMS5 in autotetraploid rice helped more pollen development which led to increasing rate of seeds [69] .

4. Enhancing Abiotic & Biotic Stress Tolerance

That polysomic polyploid plants increased abiotic stress tolerance and biotic resistance was clearly observed in coping with adversely environmental conditions. In case of salinity stress, polysomic polyploid flora used several processes to adapt to high salt concentration condition such as increasing Na+ extrusion in root, higher Na+ transport to leaf, adjust osmotic, enhanced of genes expression related to antioxidant, mitigating ROS, photosynthesize cues, phytohormone transduction cues, protein processing, regulated transcription factors, changing SNP marker related to salt stress, upregulation of aquaporin genes, up-regulated ATP synthase to enhance ion transport changing proton; using miRNAs [70] - [79] . To cope with drought stress, polysomic polyploid plants used miRNAs pathways and target genes related to transcriptional regulation, hormone metabolism and plant defense, an increase in ABA content [80] [81] [82] [83] [84] . Activation of antioxidant defense systems supported heat tolerance [85] . Polysomic polyploid plants enhanced cold stress tolerance by increasing antioxidant and epigenetic [86] [87] . Autotetraploid enhanced boron by changing root anatomical characters and copper tolerance by enhanced Cu transport gene, activation of antioxidative defense, positive regulation of expression ABA-responsive genes [88] [89] . Autopolyploid birch plant (Betula platyphylla) increased ability to NaHCO₃ stress tolerance by enhancing expression of some genes related to proline biosynthesis [90] . Autopolyploid enhanced to resistance of Venturia by significantly increased Rvi6 resistance gene-locus [91] . Likewise, Autotetraploid potato increased common scab resistance after crossing 2n gametes from diploid Solanum chacoense [92] .

5. More Adaptation Ecology

Polyploidization is one of the major adaptation ecologies such by focusing on growth, morphological traits as well as ecology invasion, pollinators [93] . After polyploidisation, the cell size increased to lead to change physiological manners with their environmental condition as well as combining multiple novel alleles and altering regulatory processes can create new potentially advantageous morphological variation. These are to expand ecological space to polyploidy plants [94] . The adaptive potential from polyploidy Arabidopsis thaliana is caused by the increase resources of TE insertions in higher ploidy plant [95] . One of priorities in genotype development is to gain through combination of potential traits which benefits in stress tolerance and nutritional aspects as a way to reduce the effects of climate change [96] . The view is that polyploidization contributes to better adapting environment in terms of suitability for growth and other benefits of cell size. Breeders can benefit immensely from more ecological adapting after polyploidisation since it improves potential traits as a whole.

6. Prospect of Polyploidy Potato Is a Main Non-Grain Staple Food

The statistics display the world’s population will reach 9.7 billion people by 2050 so this leads to 70% increase in food demand [97] . Producing more food, however, in conditions having the same or less resources will become the huge challenges for human beings. The global food need can be met by the potato crop because of diversities of cultivation and environment which are gained by being adaptable, high yielding and nutrition-rich. Productivity improvement can be achieved by the way of increasing yield or expanding areas where potatoes grown. Nowadays, a potato staple food accounts for the production of 380 million metric tons according to Faostat 2019, and contributes for 1.3 billion people worldwide with popularly increasing the nutritious tubers [98] . Besides, the potato’s adaptation with several soils and climates with being widely located from plain to high mountain regions of 4700 m compared with the sea level and also resist new drawbacks from biotic and abiotic are concerned [99] . Potato also impacts on society due to its having majority of nutrition and economy, especially with developing countries where potato output surpasses that in the other part of worldwide in ensuring food security [100] [101] . Being a source of employment and income also help to improve global food security from potato in developing countries due to the fact that potato can provide the major of vitamins, mineral, phytonutrients starch, protein as well as a source of energy and micronutrients [102] [103] [104] . Thus, potato utilizes water more efficiently than that for cereal crops that were up seven times (International Potato Center (CIP) 2018). With regard to the biodiversity, over 4000 native varieties including more than 180 wild relative potato were recorded [105] . In addition to being polyploidy, potato seems to be one of the most complex genetic modes with the various ploidy levels such as 76% were identified diploids, 3% triploids, 12% tetraploids, 2% pentaploids, and 7% hexaploids, among which tetraploid has the highest yield due to more level of genetic heterogeneity [106] [107] [108] . The practically empirical proofs shown that there were an existance of two groups of cultivated potato, one existed in high Andes of northern and central South America called the Andigenum group which consists of wide range of ploidy level, and the others are distributed in the lowlands southern Chile named the Chilotanum group which is tetraploid only [109] .

In the history of potato development, the farmers have carefully selected potato to maintain the diversity of high landraces in the native field based on 1) giving that features of flavor, textures, color and shapes to enhance their diet; 2) providing cultivars that are capable of abiotic tolerance and biotic tolerance (diseases, pests) to assure the survival and harvesting; 3) contributing in special consuming in food processing or ceremonial cultures [109] . To succeed in selecting the right traits after full testing and to create the number of seed tubers which supply to farmers, the breeders can take at least 15 years due to commercial potato being tetraploid contains four copies of each chromosome, hundreds of thousands of seedlings must be created and tested to select just one with the potential traits [99] . Moreover, with the biological features making hereditary improvement in potato was more complexity than in other staple crops, a powerful and effective approach conducted by potato breeders was the unique capacity of among ploidy and wild relative potato to cross as a way to introgress favorable agronomic traits derived from their genetic pools into the aim of the potato breeding strategies [110] [111] . For instance, the genetic diversity of Japanese potato cultivar was broadened by breeding with Andigena [112] . In another study, QTL associated with disease such Early Blight in tetraploid potato was identified in specific chromosomes [113] . The major QTL which is scab resistance originated from Solanum chacoense has introgressed into tetraploid offspring to exhibit stability in common scab resistance [92] [114] . The two traits of tuber starch and plant maturity were mapped by QTL to support the prospect of breeding potato programs [115] . A large number of elite traits in tetraploid potato linked to transcripts relating to development processes such as growth rate, high yield, tuber greening and early flowering … as well as biotic resistance were investigated to elucidate the relationship between phenotype and gene expression [116] . In addition to the flavor and textural traits having identified genes and marker related to beneficial alleles may contribute to improve nutritional basis of novel potato cultivars [117] . Several traits correlation to abiotic and biotic stress have been investigated and utilized as an artificial selection marker in breeding programs, including both modern and conventional methods. However, that the adverse effects could be created by accumulating rapidly deleterious mutations during the polyploidisation of potato notes that in development novel crops [118] . Based on studying transcriptome of cultivated potato varieties, it is revealed that tetraploid potato confers the genetic diversity of the high heterozygous [119] . With the genomic era becoming more useful than ever, it is more efficient to introgress multi-genic traits which will make it possible to utilize recessive alleles and identify rare alleles. Potato cultivars containing favorable agronomic traits must be evaluated and planted in order to ensure high yield [120] . Using Next Generation genome sequence to study six polyploidy potato genomes revealed that valuable genetic resources relating to traits derived from native landraces have functioned in disease and pest resistances as well as nutrition and fiber using breeding strategies [121] . Advances in technology are successfully applied in developing new potato cultivar. For example, the CRISPR/cas 9 was also applied in tetraploid potato to successfully knockout StPDS gene or nucleotide transitions and transversions in the StALS1 gene by introduction of simultaneous nucleotides [122] [123] . This is essential for success to breeders for crop improvement goals [124] .

7. Conclusion

In brief, due to advances in biotechnology, polyploidization is now capable of potentially making various crops containing favorable agronomic traits. While it is accepted that allopolyploid plants can often have positive effects on agriculture, other views of autopolyploid ones are significantly more important. Obviously, using autopolyploid developed by sexual or asexual method can be advantageous for reasons related to biomass, effectiveness on changing process of development, and lots of benefits on coping with climate changes. Concerning the former, whole genome doubling can perform better than (di)haploid counterparts, and as a result utilizing autopolyploid enables gaining not only gigantic effect but also increasing phytochemical content. As far as ecological prospects are concerned, autopolyploids are comparatively more effective than (di)haploid ones due to enhancing biotic and abiotic tolerance to adapt to climate change. Eventually, autopolyploid plants can also be more beneficial in the process of development that is adequate enough which provides breeders with a wide range of options when they need. It seems to human beings that the technological progress which allows us to perform autopolyploid development via unreduced gametes and somatic chromosome doubling does outweigh the benefits involved. With climate change becoming more serious than ever, we should create more elite crops as a way to address this problem assuring food security to those living on our planet. The polyploidy plants gained by sexual and asexual or somatic chromosomal doubling may affect how successful they are in their future crops development. It is unquestionable that polyploidy, whether sexual or somatically doubled chromosomes, is essential for success in gaining favorable agronomic traits.

Acknowledgements

Pham Van Hieu thanks the financial support from Ho Chi Minh City Government through HCMC Biotechnology center for his academic study and research in Japan

Conflicts of Interest

The author declares no conflicts of interest regarding the publication of this paper.

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