AtHB5 negatively regulates other HD-Zip I and it is involved in the lignification of Arabidopsis stems

ZAPATA CA; CHAN RL ; CABELLO JV

Córdoba

Congreso; 52 th Annual Meeting Argentine Society for Biochemistry and Molecular Biology; 2016

HD‐Zips are plant specific transcription factors (TFs) combining an Homeobox Domain (HD) and a Leucine Zipper (Zip). AtHB5 is an HD-Zip I transcription factor from Arabidopsis thaliana. It was previously reported that a group of HD-Zip I TFs modified its expression during lignification process in Arabidopsis stems. Interestingly, while AtHB7 and AtHB12 increased its expression during stem maturation, AtHB5 decreased it and it was the only HD-Zip I that exhibited this behavior. Mutants and overexpressing lines were obtained. In athb5 plants, AtHB7, AtHB12, AtHB6 and AtHB16 were down-regulated, while in 35S:AtHB5plants they were up-regulated. A phenotypic characterization showed that athb5 plants had a little delay in their life cycle, they had smaller rosette leaves and their branches were bended compared to WT. Plants expressing athb5xPromDR5:GUS showed that auxins were involved in the branch bending of athb5 plants. In mature plants, athb5 stems were wider and more lignified than WT stems and 35S:AtHB5 stems were narrowed and less lignified than WT ones. Furthermore, athb5 stems exhibit more phloem vessels and less xylem than WT. This characteristic was seen in vascular tissue from leaves too. We propose that AtHB5 in a negative regulator of AtHB7, AtHB12, AtHB6 and AtHB16 and it is implicated in the lignification process during stem maturation.