Functional diversity in plant HDZip subfamily I transcription factors. Using phylogenetic and motif discovery approaches to look beyond conserved domains

ARCE, AGUSTÍN L.; RAINERI, JESICA; CAPELLA, MATÍAS; CABELLO, JULIETA V.; CHAN, RAQUEL L.

Córdoba, Córdoba

Congreso; II Congreso Argentino de Bioinformática y Biología Computacional; 2011

Asociación Argentina de Bioinformática y Biología Computacional

BackgroundPlant HDZiptranscription factors are modular proteins in which a homeodomain is associated to a leucinezipper. Of the four subfamilies in which they are divided, the tested members from subfamily I bind in vitro thesame pseudopalindromic sequence CAAT(A/T)ATTG and among them, several exhibit similar expressionpatterns. However, most experiments in which HDZipI proteins were over or ectopically expressed under thecontrol of the constitutive promoter 35S CaMV resulted in transgenic plants with clearly different phenotypes.Aiming to elucidate the structural mechanisms underlying such observation and taking advantage of theincreasing information in databases of sequences from diverse plant species, an in silico analysis was performed.In addition, some of the results were also experimentally supported.ResultsA phylogenetic tree of 178 HDZipI proteins together with the sequence conservation presented outside the HDZipdomains allowed the distinction of six groups of proteins. A motifdiscoveryapproach enabled therecognition of an activation domain in the carboxyterminalregions (CTRs) and some putative regulatorymechanisms acting in the aminoterminalregions (NTRs) and CTRs involving sumoylation and phosphorylation.A yeast onehybridexperiment demonstrated that the activation activity of ATHB1, a member of one of thegroups, is located in its CTR. Chimerical constructs were performed combining the HDZipdomain of onemember with the CTR of another and transgenic plants were obtained with these constructs. The phenotype ofthe chimerical transgenic plants was similar to the observed in transgenic plants bearing the CTR of the donorprotein, revealing the importance of this module inside the whole protein.ConclusionsThe bioinformatical results and the experiments conducted in yeast and transgenic plants strongly suggest thatthe previously poorly analyzed NTRs and CTRs of HDZip I proteins play an important role in their function,hence potentially constituting a major source of functional diversity among members of this subfamily.