Auxin signaling module OsSK41-OsIAA10-OsARF regulates grain yield traits in rice

Auxin is an important phytohormone in plants, and auxin signaling pathways in rice play key roles in regulating its growth, development, and productivity. To investigate how rice grain yield traits are regulated by auxin signaling pathways and to facilitate their application in rice improvement, we validated the functional relationships among regulatory genes such as OsIAA10, OsSK41, and OsARF21 that are involved in one of the auxin (OsIAA10) signaling pathways. We assessed the phenotypic effects of these genes on several grain yield traits across two environments using knockout and/or overexpression transgenic lines. Based on the results, we constructed a model that showed how grain yield traits were regulated by OsIAA10 and OsTIR1, OsAFB2, and OsSK41 and OsmiR393 in the OsSK41-OsIAA10-OsARF module and by OsARF21 in the transcriptional regulation of downstream auxin response genes in the OsSK41-OsIAA10-OsARF module. The population genomic analyses revealed rich genetic diversity and the presence of major functional alleles at most of these loci in rice populations. The strong differentiation of many major alleles between Xian/indica and Geng/japonica subspecies and/or among modern varieties and landraces suggested that they contributed to improved productivity during evolution and breeding. We identified several important aspects associated with the genetic and molecular bases of rice grain and yield traits that were regulated by auxin signaling pathways. We also suggested rice auxin response factor (OsARF) activators as candidate target genes for improving specific target traits by overexpression and/or editing subspecies-specific alleles and by searching and pyramiding the ‘best’ gene allelic combinations at multiple regulatory genes in auxin signaling pathways in rice breeding programs.