Ectopic expression of UGT84A2 delayed flowering by indole-3-butyric acid-mediated transcriptional repression of ARF6 and ARF8 genes in Arabidopsis

Key message Ectopic expression of auxin glycosyltransferase UGT84A2 in Arabidopsis can delay flowering through increased indole-3-butyric acid and suppressed transcription of ARF 6, ARF8 and flowering-related genes FT, SOC1, AP1 and LFY . Auxins are critical regulators for plant growth and developmental processes. Auxin homeostasis is thus an important issue for plant biology. Here, we identified an indole-3-butyric acid (IBA)-specific glycosyltransferase, UGT84A2, and characterized its role in Arabidopsis flowering development. UGT84A2 could catalyze the glycosylation of IBA, but not indole-3-acetic acid (IAA). UGT84A2 transcription expression was clearly induced by IBA. When ectopically expressing in Arabidopsis, UGT84A2 caused obvious delay in flowering. Correspondingly, the increase of IBA level, the down-regulation of AUXIN RESPONSE FACTOR 6 ( ARF6 ) and ARF8 , and the down-regulation of flowering-related genes such as FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CO1(SOC1), APETALA1 (AP1) , and LEAFY(LFY) were observed in transgenic plants. When exogenously applying IBA to wild-type plants, the late flowering phenotype, the down-regulation of ARF6, ARF8 and flowering-related genes recurred. We examined the arf6arf8 double mutants and found that the expression of flowering-related genes was also substantially decreased in these mutants. Together, our results suggest that glycosyltransferase UGT84A2 may be involved in flowering regulation through indole-3-butyric acid-mediated transcriptional repression of ARF6, ARF8 and downstream flowering pathway genes.