EFFECT OF POLYPLOIDIZATION ON THE TRASCIPTOME AND METABOLOME IN SINTETHIC POLYPLOIDS OF SOLANUM spp

Abstract

Polyploidy is very common within angiosperms. Extensive studies are available only in synthetic allopolyploids. By contrast, less is known about the consequences of autopolyploidization. Our research aimed to assess the occurrence and extent of transcriptional and metabolomic changes occurring after oryzaline-induced polyploidization of Solanum commersonii and S. bulbocastanum, two diploid (2n=2×=24) potato species widely used in breeding programmes. Whole-genome expression profiling of diploid and the synthetic tetraploids they derived from were studied in both species to identify the genes exhibiting ploidy-dependent expression changes. Using a Combimatrix CustomArray 90K chip we found about 10% of all the transcriptome. Most of responses to polyploidization were species- and genotype-dependent. Comparing 4x versus 2x, it was clear that in S. commersonii a higher number of differentially expressed genes than in S. bulbocastanum, was observed. Interestingly, we found three genes whose expression changed in both species in a ploidy linked way. Bioinformatics analyses allowed to identify changes in expression “carbohydrates metabolism” and “stress response” genes in S. bulbocastanum and S. commersonii polyploids. A “global” metabolomics profiling was carried out on 170 targeted molecules by LC-ESI(+)-MS analysis. We observed a surprising metabolome alteration in the tetraploids of both species, in disagreement with previous studied reporting only few metabolic alterations associated to genome doubling. A major qualitative and quantitative impact was found in S. commersonii tetraploids. By contrast, in S. bulbocastanum lower changes occurred in important metabolite classes (glycoalkaloids, sugars). In particular, the anthocyanin pathway in tetraploids versus diploids comparisons was significantly affected, in both species. Therefore, a deeper investigation on the molecular causes beyond such accumulation was carried out. We studied the expression of R2R3 MYB an1 transcriptional factor, ans and dfr genes. In S. bulbocastanum our results on gene expression analyses were consistent with the down-accumulation found in tetraploids respect to diploid parent. By contrast, in S. commersonii polyploids the gene expression profiles were not consistent with the drastic accumulation of anthocyanins observed. Further investigations are required, but we believe that answering to this question may produce an important scientific finding with practical breeding applications.