A Gain-of-Function Mutation in IAA7/AXR2 Confers Late Flowering under Short-day Light in Arabidopsis

Floral initiation is a major step in the life cycle of plants, which is influenced by photoperiod, temperature, and phytohormones, such as gibberellins （GAs）. It is known that GAs promote floral initiation under short-day light conditions （SDs） by regulating the floral meristem-identity gene LEAFY （LFY） and the flowering-time gene SUPPRESSOR OF OVEREXPRESSION OF CO 1 （SOC1）. We have defined the role of the auxin signaling component INDOLE-3-ACETIC ACID 7 （IAA7）/AUXIN RESISTANT 2 （AXR2） in the regulation of flowering time in Arabidopsis thaliana. We demonstrate that the gain-of-function mutant of IAA7/AXR2, axr2-1, flowers late under SDs. The exogenous application of GAs rescued the late flowering phenotype of axr2-1 plants. The expression of the GA20 oxidase （GA2Oox） genes, GA2Ooxl and GA2Oox2, was reduced in axr2-1 plants, and the levels of both LFY and SOC1 transcripts were reduced in axr2-1 mutants under SDs. Furthermore, the overexpression of SOC1 or LFY in axr2-1 mutants rescued the late flowering phenotype under SDs. Our results suggest that IAA7/AXR2 might act to inhibit the timing of floral transition under SDs, at least in part, by negatively regulating the expressions of the GA2Ooxl and GA2Oox2 genes.