A GSK3 FAMILY MEMBER SK12 REGULATES FLOWERING THROUGH MEDIATING THE STABILITY OF CONSTANS IN ARABIDOPSIS THALIANA

Abstract

Photoperiod pathway regulates flowering in response to the day length mainly through CONSTANS (CO) by directly promoting the expression of FLOWERING LOCUS T (FT) under long days. Recently, it has been reported that CO is phosphorylated before degradation. However, the kinase(s) that phosphorylate CO remain unknown. Here, we report that a GLYCOGEN SYNTHASE KINASE 3 (GSK3) member SHAGGY-like kinase 12 (SK12) regulates flowering time through phosphorylating CO and thus affecting CO protein stability. Loss of function of SK12 results in an early-flowering phenotype, which is partly due to increased expression of FT. SK12 and CO mainly interact in the nuclei. SK12 phosphorylates CO. We further show that the CO abundance is higher in sk12-1 than in WT, indicating that CO is much more stable in sk12-1. Our results suggest a new flowering mechanism by which SK12 phosphorylates CO and negatively regulates its protein stability, thus affecting flowering time in Arabidopsis.