BBX24 acts as a positive regulator to promote hypocotyl elongation in shade avoidance responses

CROCCO, CARLOS; SANTIAGO MORA GARCIA; BOTTO, JAVIER

Mendoza

Congreso; XLVIII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2012

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Plants grown at high densities perceive through the phytochrome system a decrease in the red to far-red (R:FR) ratio of incoming light, as a warning signal of future competition, and mount morphological responses collectively known as the shade avoidance syndrome (SAS). In Arabidopsis thaliana seedlings, the hypocotyl elongation by SAS involves a rapid up-regulation of known shade marker genes activating an interacting network of various hormones that will eventually lead to cell elongation. We identified and characterized a group of B-box (BBX) proteins as new components involved in the SAS signaling pathway, which act as positive (BBX18 and BBX24) or negative (BBX19, BBX21 and BBX22) regulators. By microarray analysis, pharmacological and genetic approaches, we investigated the molecular action of BBX24 in the SAS. Global expression analysis of wild-type and bbx24 seedlings reveals that a large number of genes involved in hormonal signaling pathways are positively regulated by BBX24 in response to shade, particularly genes involved in gibberellin (GA) biosynthesis. We found that exogenous GA recovers the hypocotyl elongation of bbx24 mutant seedlings in shade conditions. In addition, the phenotype of pif4 bbx24 double mutants suggests that BBX24 is involved in the GA signaling pathway mediated by PHYTOCHROME INTERACTING FACTOR 4 (PIF4).