The function of OsRAD51A1 gene in meiotic stability and high seed-setting rate of tetraploid rice

This study demonstrates the critical role of OsRAD51A1 in maintaining meiotic stability in tetraploid rice, which can improve the seed-setting rate and promote the development of polyploid rice. Polyploid rice has a range of significant advantages over diploid rice. However, low seed-setting rates seriously limited development of polyploid rice for several decades until polyploid meiosis stability (PMeS) lines with high seed-setting rate were bred. Three meiotic genes were identified as candidates associated with stable meiosis and high seed-setting rate in PMeS lines. The function of one candidate gene, OsRAD51A1, in tetraploid rice was investigated in this study. Throughout the whole young panicle development period, OsRAD51A1 expression level in PMeS line A1-4x was higher than that in non-PMeS line NG46-4x, with A1-4x showing peak expression at meiosis stage; meanwhile, the methylation level of promoter CpG island in NG46-4x was consistently higher than that in A1-4x. The OsRAD51A1 was localized to nucleus. Following RNAi-mediated silencing of OsRAD51A1 in PMeS line A1-4x, chromosomal behavior during meiosis became disordered, pollen development was abnormal, pollen malformation rate increased, ratios of fertile and viable pollen decreased significantly, and seed-setting rate was significantly reduced. Conversely, OsRAD51A1 overexpression in non-PMeS line NG46-4x effectively normalized chromosomal behavior during meiosis and pollen development, morphology, fertility, and viability, and seed-setting rate increased significantly. It is inferred that loss of OsRAD51A1 leads to an increased number of univalents and multivalents during prophase I in tetraploid rice, further affecting development and fertility of gametes, and resulting in decreased seed-setting rate. OsRAD51A1 may play a pivotal role in the process of homologous chromosome pairing, recombination, and ultimately affects the tetraploid rice seed-setting rate.