Isolation and Genomic Characterization of Heat Tolerant Mutant Lines from Micro-Tom Mutant Collections

Heat stress higher than 35/25℃ day/night reduces the pollen fertility and seriously affects tomato fruits production. According to the research of Intergovernmental Panel on Climate Change (IPCC), the temperature of global surface will get 0.2℃ forward 10 years. Hence, the high temperature stress will be a major problem in the future society. In this research, we isolated heat tolerant tomato lines conferring improved fruits setting ability under high temperature condition from Micro-Tom mutant collections generated by EMS treatment.

We grew the mutant collections under high temperature condition, and isolated 15 mutant lines. Although fruits harvested from all lines contained seeds, one of the mutant lines, HT7 showed higher number of fruits with seeds than WT. It was suggested that HT7 succeeded in pollination under high temperature condition due to the production of more viable pollen than WT. We evaluated total pollen number and pollen viability of WT and HT7 using TTC (2,3,5-Triphenyltetrazolium chloride) staining method. Both of pollen number and pollen viability of HT7 were higher than those of WT.

To identify the candidate gene for heat tolerance of HT7, we read the whole genome of HT7 by next-generation sequencer. As a result, 181 SNPs were detected in the coding sequence of whole genome, and 159 genes were mutated. Among the SNPs in 159 candidate genes, 31 SNPs showed change of amino acids by nonsense or missense mutation. Therefore, it is likely that those mutations in the 31 genes account for heat tolerance phenotype of HT7.