Functional and biochemical characterisation of the HD-Zip I transcription factor MTHB1 from M. truncatula.

ARIEL FEDERICO DAMIÁN; DIET ANOUCK; GRUBER VERONIQUE; FRUGIER FLORIAN; CHAN RAQUEL LÍA; CRESPI MARTIN

Carlos Paz

Congreso; Reunión Anual de la SAIB; 2008

SAIB

MTHB1 belongs to the HD-Zip family of transcription factors (TFs) from the model legume Medicago truncatula. It was first identified because its expression in roots increases in response to high NaCl concentrations. The full length cDNA of MTHB1 was isolated and the codified protein expressed in bacteria. Electrophoretic mobility shift assays performed with the purified protein revealed that MTHB1 recognises in vitro the sequence CAAT(N)ATTG with the highest affinity, as other characterised members of the HD-Zip I subfamily. This DNA core was used to identify direct target genes of this TF in alternative transcriptional approaches. The validation of this box as a functional cis-acting element in the promoter regions of putative target genes is actually being carried out. The MTHB1 expression pattern in separate tissues and organs from the whole plant was determined by quantitative RT-PCR, both in normal conditions and in response to alternative environmental factors. Besides, the promoter region of MTHB1 was also isolated and cloned in a binary vector fused to the reporter gene GUS. A detailed expression pattern was then unravelled in roots of Medicago composite plants.  Overexpression of MTHB1 cDNA in Medicago roots resulted in a phenotype distinguishable from the wild type. Further functional analyses are now being undertaken also with mthb1 TILLING mutants. The information obtained from the different approaches is helping to understand how this TF participates in root architecture determination.