Genome-wide analysis of DNA polymorphisms, the methylome and transcriptome revealed that multiple factors are associated with low pollen fertility in autotetraploid rice

Autotetraploid rice is a useful germplasm with high biomass production; however, low fertility is the main barrier in commercial utilization. In our previous study, differential expression of meiosis-related miRNAs was found to be involved in the pollen sterility of autotetraploid rice. However, genome-wide DNA variations and methylomes associated with low fertility of autotetraploid rice are still poorly understood. Here, we measured both global DNA variations and the methylome and compared them with the transcriptome during pollen development in autotetraploid rice by high-throughput sequencing. A total of 34416 SNPs, 6993 InDels, 1003 SVs and 25 CNVs were detected, and 11367 and 41117 differentially methylated regions showed hypermethylation and hypomethylation in 02428-4x. In total, 1110 genes displayed differentially expression in 02428-4x during meiosis, of these six harbored CNVs, including four upregulated genes with gain CNVs, such as LOC_Os11g38620. We identified 122 genes by comparing with the previous data that might be associated with low fertility during pollen development in 02428-4x. Of the 122 gens, 98 were displayed methylation and differential expression, including OsMADS98, CYP703A3 and OsABCG26. The downregulation of these three genes were confirmed by qPCR during meiosis of 02428-4x, which played pivotal roles in pollen fertility. These results indicate that the low fertility of autotetraploid rice is not only caused by the differential expression of genes involved in pollen development, but also by sequence variation and differential methylation, suggesting that the reason for pollen sterility in autotetraploid rice is complex and might be affected by multiple factors.