Flowering in Response to Cold

Abstract

Flowering in Arabidopsis is coordinated through numerous genes that are responsive to factors such as day length and exposure to cold, ensuring that the plant will flower under the most appropriate conditions. Plants adapted to northern latitudes, for instance, flower earlier following prolonged exposure to cold during germination, a process called vernalization. FLC (FLOWERING LOCUS C), which acts a flowering repressor, plays a key role in vernalization; FLC expression decreases during vernalization so that flowering can take place. However, null flc mutants still show a vernalization response, suggesting that multiple genes regulate this complex process. Ratcliffe et al. used mutational analysis to analyze the effects of four genes closely related to FLC , MAF2 ( MADS AFFECTING FLOWERING ) through MAF5 . The authors investigated the effects of MAF2 loss-of-function and gain-of-function mutants on flowering in unvernalized plants or plants exposed to cold for different durations. The maf2 -null mutant flowered earlier after brief periods of cold that did not affect flowering in wild-type plants, whereas MAF2 overexpression prevented vernalization. In contrast to FLC , which declined throughout the period of cold exposure, MAF2 levels only declined following prolonged cold exposure. Thus, MAF2 appears to prevent premature flowering following brief cold spells. Overexpression of MAF3 , MAF4 , and MAF5 could all delay flowering. MAF5 mRNA increased during vernalization, leading the authors to postulate that MAF5 might act as a floral activator by competing with more potent floral repressors such as FLC . Thus, the closely related FLC , MAF2 , and MAF5 genes all play distinct roles in the vernalization process. O. J. Radcliffe, R. W. Kumimoto, B. J. Wong, J. L. Riechmann, Analysis of the Arabidopsis MADS AFFECTING FLOWERING gene family: MAF2 prevents vernalization by short periods of cold. Plant Cell 15 , 1159-1169 (2003). [Abstract] [Full Text]