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). FLM transcripts can undergo extensive alternative splicing producing multiple variants, of which FLM-b and FLM-d are the most representative. While FLM-b codes for the flowering repressor FLM protein, translation of FLM-d 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 FLM, balancing the levels of FLM-b and FLM-d across the ambient temperature range. In the absence of the CDKG2/CYCL1 complex, FLM-b expression is reduced while FLM-d is increased in a temperature dependent manner and these changes are associated with an early flowering phenotype in the cdkg2 mutant lines. In addition, we found that transcript variants retaining the full FLM intron 1 are sequestered in the cell nucleus. Strikingly, FLM intron 1 splicing is also regulated by CDKG2/CYCL1. Our results provide evidence that temperature and CDKs regulate the alternative splicing of FLM, contributing to flowering time definition.

A Functional Kinase Is Necessary for Cyclin-Dependent Kinase G1 (CDKG1) to Maintain Fertility at High Ambient Temperature in Arabidopsis

“…The suggestion that the CDKG1 gene has arisen from a retrotransposition event from the CDKG2 gene in the Arabidopsis lineage after the split from other Brassicaceae ( Zhang et al, 2005 ; Beilstein et al, 2010 ) has raised questions related to their function and why both genes have been retained. Even though CDKG1 and CDKG2 proteins share 64% amino acid similarity, we and others have shown that the two kinases perform different functions ( Huang et al, 2013 ; Zheng et al, 2014 ; Ma et al, 2015 ; Cavallari et al, 2018 ; Chen et al, 2018 ; Nibau et al, 2020a , b ). On the other hand, we were not able to recover double cdkg1-1cdkg2-1 mutants despite both single mutants showing only mild growth phenotypes.…”

“…Studies in somatic tissues suggest that both CDKG1 and its homolog CDKG2 perform distinct functions in regulating gene splicing ( Huang et al, 2013 ; Cavallari et al, 2018 ; Nibau et al, 2020a ). On the other hand, while each single mutant is viable, we cannot recover a double cdkg1-1cdkg2-1 mutant, suggesting that their functions do overlap and are essential.…”

“…In vegetative tissues, CDKG1 regulates the AS of the splicing factor U2AF65A , and in pollen, it regulates the AS of CalS5 mRNA ( Huang et al, 2013 ; Cavallari et al, 2018 ). CDKG2 regulates the AS of FLOWERING LOCUS M ( FLM ) to fine tune flowering time in Arabidopsis according to environmental temperature ( Nibau et al, 2020a ). Importantly, in vegetative tissues CDKG2 controls the temperature-dependent AS of CDKG1 ( Cavallari et al, 2018 ).…”

Temperature-Dependent Alternative Splicing of Precursor mRNAs and Its Biological Significance: A Review Focused on Post-Transcriptional Regulation of a Cold Shock Protein Gene in Hibernating Mammals

“…One of the regulators that have been characterized in detail is flowering locus M ( FLM ), which is a MADS-domain transcription factor [ 16 , 23 , 27 , 28 ]. FLM is subjected to temperature-dependent alternative splicing in Arabidopsis [ 23 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Two splice variants of FLM , FLM-β and FLM-δ , differ in the incorporation of either the second or third cassette exon [ 11 , 27 , 37 ].…”

“…Temperature can modulate the splicing of splicing regulators. For example, U2AF65A [ 88 ], cyclin-dependent kinase G1 ( CDKG1 ) [ 33 , 88 ], SR1 [ 89 ], polypyrimdine tract-binding protein ( PTB ) 1/2 , and suppressor of abi3-5 ( SUA ) [ 90 ], which affect the splicing pattern, are subjected to temperature-dependent alternative splicing in Arabidopsis. In animals, the splicing of pre-mRNA of U2AF26 in mice [ 70 , 75 , 76 ] and serine-arginine-rich (SR) splicing factors in Tilapia [ 72 ] are also regulated by change in temperature.…”