Uncharacterized conserved motifs outside the HD-Zip domain in HD-Zip subfamily I transcription factors; a potential source of functional diversity

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

BMC PLANT BIOLOGY

BIOMED CENTRAL LTD

Lugar: Londres; Año: 2011 vol. 11 p. 42 - 42

1471-2229

Background: Plant HD-Zip transcription factors are modular proteins in which a homeodomain is associated to aleucine zipper. Of the four subfamilies in which they are divided, the tested members from subfamily I bind in vitrothe same pseudopalindromic sequence CAAT(A/T)ATTG and among them, several exhibit similar expressionpatterns. However, most experiments in which HD-Zip I 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 the increasinginformation in databases of sequences from diverse plant species, an in silico analysis was performed. In addition,some of the results were also experimentally supported.Results: A phylogenetic tree of 178 HD-Zip I proteins together with the sequence conservation presented outsidethe HD-Zip domains allowed the distinction of six groups of proteins. A motif-discovery approach enabled therecognition of an activation domain in the carboxy-terminal regions (CTRs) and some putative regulatorymechanisms acting in the amino-terminal regions (NTRs) and CTRs involving sumoylation and phosphorylation.A yeast one-hybrid experiment demonstrated that the activation activity of ATHB1, a member of one of thegroups, is located in its CTR. Chimerical constructs were performed combining the HD-Zip domain of one memberwith the CTR of another and transgenic plants were obtained with these constructs. The phenotype of thechimerical transgenic plants was similar to the observed in transgenic plants bearing the CTR of the donor protein,revealing the importance of this module inside the whole protein.Conclusions: The bioinformatical results and the experiments conducted in yeast and transgenic plants stronglysuggest that the previously poorly analyzed NTRs and CTRs of HD-Zip I proteins play an important role in theirfunction, hence potentially constituting a major source of functional diversity among members of this subfamily.