FIERY1 regulates light‐mediated repression of cell elongation and flowering time via its 3′(2′),5′‐bisphosphate nucleotidase activity

Light is one of the most important environmental factors that regulate plant development. Here we report that a mutation in the Arabidopsis FIERY1 gene (FRY1) caused a shortened hypocotyl and shorter petioles, most dramatically under low-intensity red light and less pronounced under far-red and blue-light conditions. Furthermore, the fry1 mutant flowered late, probably due to a reduced level of FLOWERING LOCUS T (FT) transcript. However, although the transcript level of FRY1 was light-regulated, the chlorophyll level and the expression of typical light-regulated genes were not affected in the fry1 mutant. FRY1 is known as a regulator of abiotic stress responses, and its protein product has dual enzymatic activity comprising inositol polyphosphate-1-phosphatase and 3'(2'),5'-bisphosphate nucleotidase activity. Genetic complementation data obtained using cDNA of the FRY1 paralog AHL (Arabidopsis HAL2-like) and the similar phenotype of an xrn2/xrn3 double mutant suggest that FRY1 attenuates light responses via its 3'(2'),5'-bisphosphate nucleotidase activity rather than its inositol polyphosphate-1-phosphatase activity. We discuss the relationship between the FRY1-associated nucleotidase activity, a step in the pathway for sulfur metabolism and utilization, and the Arabidopsis light response.