ATHB1, AN ARABIDOPSIS HD-ZIP I TRANSCRIPTION FACTOR, IS INVOLVED IN HYPOCOTYL ELONGATION

CAPELLA, MATIAS; RIBONE, PAMELA A; CHAN, RAQUEL L

Rosario

Congreso; XLIX Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2014

Homeodomain-leucine zipper (HD-Zip) transcription factors are only present in the plant kingdom and have been involved in developmental processes associated to environmental conditions. AtHB1, an Arabidopsis thaliana HD-Zip I member, has been previously described as a transcriptional activator, probably involved in leaf development. However, up to date its function is still largely unknown. Here we show that AtHB1 is mainly expressed in hypocotyls of seedlings grown under a short photoperiod regime. AtHB1 knock-down mutants showed longer hypocotyls than WT while AtHB1 overexpressors exhibited the opposite phenotype, especially in short-day-conditions. By measuring AtHB1 transcript levels in pif1 mutants and GUS activity in tobacco leaves co-transformed with PromAtHB 1::GUS and 35S::PIF1, it has been observed that PIF1 induces AtHB1 expression. Additionally, by analyzing athb1, pif1 and athb1/pif1 mutants and PIF1 or AtHB1 overexpressors in WT, athb1 or pif1 backgrounds, we were able to determine that PIF1 regulates AtHB 1 expression to promote hypocotyls growth. Transcriptomic approaches revealed that AtHB1 regulates several genes involved in cell wall composition and elongation. The results suggested that AtHB1 acts downstream PIF1 to regulate growth-related proteins expression to promote hypocotyl cell elongation in response to short photoperiod conditions.