Thermo-Sensitive Alternative Splicing of FLOWERING LOCUS M Is Modulated by Cyclin-Dependent Kinase G2

Abstract

The ability to sense environmental temperature and to coordinate growth and development accordingly, is critical to the reproductive success of plants. Flowering time is regulated at the level of gene expression by a complex network of factors that integrate environmental and developmental cues. One of the main players, involved in modulating flowering time in response to changes in ambient temperature is FLOWERING LOCUS M (FLM). <i>FLM</i> transcripts can undergo extensive alternative splicing producing multiple variants, of which <i>FLM-β</i> and <i>FLM-δ</i> are the most representative. While <i>FLM-β</i> codes for the flowering repressor FLM protein, translation of <i>FLM-δ</i> has the opposite effect on flowering. Here we show that the cyclin-dependent kinase G2 (CDKG2), together with its cognate cyclin, CYCLYN L1 (CYCL1) affects the alternative splicing of <i>FLM</i>, balancing the levels of <i>FLM-β</i> and <i>FLM-δ</i> across the ambient temperature range. In the absence of the CDKG2/CYCL1 complex, <i>FLM-β</i> expression is reduced while <i>FLM-δ</i> is increased in a temperature dependent manner and these changes are associated with an early flowering phenotype in the <i>cdkg2</i> mutant lines. In addition, we found that transcript variants retaining the full <i>FLM</i> intron 1 are sequestered in the cell nucleus. Strikingly, <i>FLM</i> intron 1 splicing is also regulated by CDKG2/CYCL1. Our results provide evidence that temperature and CDKs regulate the alternative splicing of <i>FLM</i>, contributing to flowering time definition.