RING Finger E3 Ubiquitin Ligase Gene TaAIRP2-1B Regulates Spike Length in Wheat.

E3 ubiquitin ligase genes play important roles in the regulation of plant development. They have been well-studied in plants, but have not been sufficiently investigated in wheat. Here, we identified a highly expressed RING finger E3 ubiquitin ligase gene TaAIRP2-1B (ABA-insensitive RING protein 2) in wheat spike. Sequence polymorphism and association analysis showed that TaAIRP2-1B is significantly associated with spike length under various conditions. The genotype with haplotype Hap-1B-1 of TaAIRP2-1B has longer spike than that of Hap-1B-2, and was positively selected in the process of wheat breeding in China. Moreover, the TaAIRP2-1B overexpressing rice lines have longer panicles compared to the wild-type plants. The expression levels of TaAIRP2-1B in Hap-1B-1 accessions were higher than in Hap-1B-2 accessions. Further study revealed that TaAIRP2-1B's expression was negatively regulated by TaERF3 (ethylene-responsive factor 3) via binding to Hap-1B-2 promoter, but not to Hap-1B-1. Additionally, several candidate genes interacting with TaAIRP2-1B were obtained by screening the cDNA library of wheat in yeast cells. Among which TaAIRP2-1B interacted with TaHIPP3 (heavy metal-associated isoprenylated protein 3) and promoted TaHIPP3 degradation. The present research demonstrated that TaAIRP2-1B regulates spike length, the haplotype Hap-1B-1 of TaAIRP2-1B is a favorable natural variation for spike length enhancement in wheat, and provided genetic resources and functional markers for wheat molecular breeding.