Arabidopsis thaliana HomeoBox 1 (AtHB1), a Homedomain‐Leucine Zipper I (HD‐Zip I) transcription factor, is regulated by PHYTOCHROME‐INTERACTING FACTOR 1 to promote hypocotyl elongation. Issue 3 (10th April 2015)

• Record Type: Journal Article
• Authors: Capella, Matías; Ribone, Pamela A.; Arce, Agustín L.; Chan, Raquel L.
• Is Part Of: New phytologist. Volume 207:Issue 3(2015)
• Page Start: 669
• Page End: 682
• Publication Date: 2015-04-10
• Subjects: Botany -- Periodicals; 580
• DOI: 10.1111/nph.13401
• Languages: English
• ISSNs: 0028-646X

Abstract

<abstract abstract-type="main" id="nph13401-abs-0001"> <title>Summary</title> <p> <list id="nph13401-list-0001" list-type="bullet"> <list-item> <p> <italic>Arabidopsis thaliana</italic> HomeoBox 1 (AtHB1) is a homeodomain‐leucine zipper transcription factor described as a transcriptional activator with unknown function. Its role in <italic>A. thaliana</italic> development was investigated.</p> </list-item> <list-item> <p> <italic>AtHB1</italic> expression was analyzed in transgenic plants bearing its promoter region fused to reporter genes. Knock‐down mutant and overexpressor plant phenotypes were analyzed in different photoperiod regimes.</p> </list-item> <list-item> <p> <italic>AtHB1</italic> was mainly expressed in hypocotyls and roots and up‐regulated in seedlings grown under a short‐day photoperiod. <italic>AtHB1</italic> knock‐down mutants and overexpressors showed shorter and longer hypocotyls, respectively, than wild type (WT). <italic>AtHB1</italic> transcript levels were lower in <italic>PHYTOCHROME‐INTERACTING FACTOR 1</italic> (<italic>PIF1</italic>) mutants than in controls, suggesting that <italic>AtHB1</italic> is regulated by <italic>PIF1</italic> in hypocotyls. β‐glucuronidase (GUS) activity in <italic>Nicotiana benthamiana</italic> leaves cotransformed with <italic>PromAtHB1::GUS</italic> and <italic>35S::PIF1</italic> indicated that PIF1 induces <italic>AtHB1</italic> expression. Hypocotyl lenght was measured in seedlings of <italic>athb1</italic>, <italic> pif1</italic>, or double <italic>athb1</italic>/<italic>pif1</italic> mutants and <italic>PIF1</italic> or <italic>AtHB1</italic> overexpressors in WT, <italic>athb1</italic> or <italic>pif1</italic> backgrounds, both in short‐ or long‐day. These analyses allowed us to determine that AtHB1 is a factor acting downstream of PIF1. Finally, a transcriptome analysis of <italic>athb1</italic> mutant hypocotyls revealed that AtHB1 regulates genes involved in cell wall composition and elongation.</p> </list-item> <list-item> <p>The results suggest that AtHB1 acts downstream of PIF1 to promote hypocotyl elongation, especially in response to short‐day photoperiods.</p> </list-item> </list> </p> </abstract>