CONSTANS–FKBP12 interaction contributes to modulation ofphotoperiodic flowering in Arabidopsis

Flowering time is a key process in plant development. Photoperiodic signals play a crucial role in the floraltransition inArabidopsis thaliana, and the protein CONSTANS (CO) has a central regulatory function that istightly regulated at the transcriptional and post-translational levels. The stability of CO protein depends ona light-driven proteasome process that optimizes its accumulation in the evening to promote the produc-tion of the florigen FLOWERING LOCUS T (FT) and induce seasonal flowering. To further investigate thepost-translational regulation of CO protein we have dissected its interactome network employingin vivoandin vitroassays and molecular genetics approaches. The immunophilin FKBP12 has been identified inArabidopsis as a CO interactor that regulates its accumulation and activity. FKBP12 and CO interact throughthe CCT domain, affecting the stability and function of CO.fkbp12insertion mutants show a delay in flow-ering time, whileFKBP12overexpression accelerates flowering, and these phenotypes can be directlyrelated to a change in accumulation of FT protein. The interaction is conserved between theChlamy-domonasalgal orthologs CrCO–CrFKBP12, revealing an ancient regulatory step in photoperiod regulation ofplant development