RPT2a-mediated degradation of WDR5a regulates flowering time in Arabidopsis.

RPT2a and CUL4-DDB1A-mediated degradation of WDR5a regulates COMPASS-like complex-dependent H3K4me3 homeostasis and flowering time in Arabidopsis through the FLC-FT/SOC1 regulatory module. The Arabidopsis complex of proteins associated with Set1 (COMPASS)-like complex plays a crucial role in regulating H3K4me3, a key histone modification associated with active transcription. Within this complex, WD40-REPEAT 5a (WDR5a) functions as a structural backbone protein, critical for maintaining proper H3K4me3 levels. WDR5a is subject to degradation via the 26S proteasome pathway, a process that significantly influences H3K4me3 dynamics. Utilizing a yeast two-hybrid screen, we identified the 26S proteasome subunit REGULATORY PARTICLE AAA-ATPASE2a (RPT2a) as an interacting partner of WDR5a, highlighting its role in WDR5a's proteasomal degradation. Further investigation revealed that the ubiquitin ligase complex Cullin4 (CUL4)-DNA Damage Binding protein 1A (DDB1A) targets WDR5a for ubiquitination, with lysine residues K31 and K211 being potential ubiquitination sites. RPT2a's involvement in WDR5a degradation consequently affects the expression of the floral repressor FLOWERING LOCUS C (FLC), thereby establishing an inverse relationship with the expression of flowering time control genes FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1). As these genes are directly repressed by FLC, their modulation via WDR5a degradation ultimately influences flowering time in Arabidopsis, underscoring the complex interplay between histone modification and plant development.