COUSINS LONG REMOVED: FUNCTIONAL CONSERVATION OF BEH TRANSCRIPTION FACTORS IN BRYOPHYTES AND ANGIOSPERMS

CAÑO-DELGADO AI; GARCÍA-HOURQUET, MARIANO; MORA GARCIA, SANTIAGO; MECCHIA, MARTIN

Congreso; Reunion Conjunta SAIB-SAMIGE 2020; 2020

SAIB-SAMIGE

Brassinosteroids (BRs) signalling pathway is one of the best characterized in plants. BRs perception by receptors of the family BRL orchestrates the organization of a membrane-associated signalling complex that inactivates GSK3 kinases. In their active form, GSK3s phosphorylate and inactivate the transcription factors of the BEH family. The latter become dephosphorylated and accumulate in the nucleus in the presence of BRs, to regulate the expression of genes involved in the process of ?growth?. Although BRs have been associated to cell division and expansion, mounting evidence also links BRs to the control of differentiation processes of meristematic tissues. BEH proteins are present in all Streptophyta from the order Klebsormidiales on, as a family with a relatively small number of members and a fairly high degree of conservation of diagnostic motifs. The liverwort Marchantia polymorpha has only one gene of this kind, MpBEH. Since this bryophyte offers many advantages to do comparative evolutionary studies, we decided to characterize the functions of this gene. Imbalances in the abundance of MpBEH cause phenotypic alterations that can be explained if MpBEH has a crucial role in cell differentiation. Coexpression of MpBEH and GSK3 kinases shows that MpBEH may be target of phosphorylation. However, no interaction was observed between MpBEH and MpGSK in yeast-two hybrid assays, suggesting that BEH proteins in bryophytes and angiosperms may be subject to different regulatory regimes. Arabidopsis lines overexpressing MpBEH show an array of phenotypic alterations that suggest a gain of function in BRs signalling: altered morphology, delayed flowering and senescence and insensitivity to a BRs synthesis inhibitor. MpBEH, escaping the regulation imposed by GSK3s, may then be able to regulate the expression of BRs-responsive genes in Arabidopsis. Indeed, the DNA motif recognized by BEH proteins in Arabidopsis is significantly enriched in the genes over-expressed in the liverwort knock-out mutant Mpbeh. This comparative study in taxa that diverged more than 400 million years ago will shed more light on the basic processes regulated by BRs.