Pollen transcriptome analysis of Solanum tuberosum (2n = 4x = 48), S. demissum (2n = 6x = 72), and their reciprocal F1 hybrids
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Pollen mRNAs were different in reciprocal F 1 hybrids, which were probably caused by a cytoplasm–nuclear chromosomal genes interaction.
We have found reciprocal differences in crossability between F1 hybrids of Solanum tuberosum (T) and a Mexican wild potato species S. demissum (D). When the reciprocal hybrids were crossed as pollen parents with S. demissum, a significantly higher berry-setting rate was obtained in TD compared with DT. In this study, we performed a whole-genome transcript analysis of the pollen mRNA using a high-throughput sequencer. We obtained 12.6 billion bases that were aligned into 13,020 transcripts with 9,366 loci. All possible genetic modes were observed between the parents and their progeny, where over-dominance and under-recessive types were relatively frequent (15.7 and 15.3 %, respectively). We found that 59.1 % of transcripts were more abundant in TD and over fourfold higher transcription levels were found in 66 TD transcripts and three DT transcripts. A higher proportion of over-dominance and a lower proportion of under-recessive transcription types were also observed in TD. The percentage contributions of multiple transcripts at the same locus varied greatly and were transcribed differently between species. In the new allelic combinations created by hybridization, approximately three-fourth of the transcripts had intermediate percentage contributions between the parents but no differential transcription patterns were apparent between the reciprocal hybrids. A broad spectrum of functionally different nuclear genes was over-represented in TD pollen, some of which were directly related to pollen behavior. Since TD and DT pollen had the same composition of nuclear genes, a cytoplasm–nuclear chromosomal genes interaction is suggested for the cause of transcriptional and phenotypic differences between reciprocal hybrids.
KeywordsPollen transcriptome Interspecific F1 hybrids Reciprocal difference Allelic variation Cytoplasm–nuclear chromosomal genes interaction
We thank the US Potato Genebank (NRSP-6), Sturgeon Bay, Wisconsin, for providing the Solanum seed used in this study and Dr. I. Sugimura, Hokkaido System Science Co. Ltd., for initial data handling and technical advice during high-throughput sequencing. We also thank Enago (http://www.enago.jp) for the English language review. This study was supported by Calbee Inc. and Calbee Potato Inc.
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