RING finger ubiquitin E3 ligase gene TaSDIR1-4A contributes to grain size in common wheat.

Salt and Drought Induced RING finger1 (SDIR1) is a RING-type E3 ubiquitin ligase that plays a pivotal role in ABA-mediated response to salinity and drought stress by the ubiquitination pathway in some plant species. However, its function in wheat (Triticum aestivum) is unknown. Here, we isolated a SDIR1 member, TaSDIR1-4A in wheat and characterized its E3 ubiquitin ligase activity. DNA polymorphism assays showed the presence of two nucleotide variation sites in the promoter region of TaSDIR1-4A; these formed haplotypes Hap-4A-1 and Hap-4A-2 that were detected in wheat populations. Association analysis showed that TaSDIR1-4A was associated with 1,000-grain weight (TGW) in all test environments, including well watered and heat stress situations. Genotypes with Hap-4A-2 had higher TGW than those with Hap-4A-1. The phenotypes in both gene-silenced wheat and transgenic Arabidopsis showed that TaSDIR1-4A was a negative regulator of grain size. Gene expression assays revealed that TaSDIR1-4A was most highly expressed in flag leaves, and expression levels of TaSDIR1-4A were higher in Hap-4A-1 accessions than in Hap-4A-2 accessions. The difference might be attributable to TaERF3 (Ethylene Response Factor) can act as a transcriptional repressor of TaSDIR1-4A in Hap-4A-2, but not of TaSDIR1-4A in Hap-4A-1. The favorable haplotype has been positively selected in breeding programs in China. The functional marker for TaSDIR1-4A should be helpful for wheat breeding.