The homeodomain-leucine zipper (HD-Zip) class I transcription factors ATHB7 and ATHB12 modulate abscisic acid signalling by regulating protein phosphatase 2C and abscisic acid receptor gene activities
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Plants perceiving drought activate multiple responses to improve survival, including large-scale alterations in gene expression. This article reports on the roles in the drought response of two Arabidopsis thaliana homeodomain-leucine zipper class I genes; ATHB7 and ATHB12, both strongly induced by water-deficit and abscisic acid (ABA). ABA-mediated transcriptional regulation of both genes is shown to depend on the activity of protein phosphatases type 2C (PP2C). ATHB7 and ATHB12 are, thus, targets of the ABA signalling mechanism defined by the PP2Cs and the PYR/PYL family of ABA receptors, with which the PP2C proteins interact. Our results from chromatin immunoprecipitation and gene expression analyses demonstrate that ATHB7 and ATHB12 act as positive transcriptional regulators of PP2C genes, and thereby as negative regulators of abscisic acid signalling. In support of this notion, our results also show that ATHB7 and ATHB12 act to repress the transcription of genes encoding the ABA receptors PYL5 and PYL8 in response to an ABA stimulus. In summary, we demonstrate that ATHB7 and ATHB12 have essential functions in the primary response to drought, as mediators of a negative feedback effect on ABA signalling in the plant response to water deficit.
KeywordsHD-Zip PP2C ABA SnRK2 ABA receptors Drought stress response
This work was supported by the European commission (TF-STRESS), The Royal Swedish Academy of Sciences, and the Lars Hiertas Minne and Nils and Dorthi Troedsson Foundations. A.E.V. was supported by postdoctoral fellowships from the Spanish Ministry of Education and Science (EX2006-1690) and the Alfonso Martín Escudero Foundation. The authors would like to thank Pedro Rodríguez for the donation of the pp2c mutants, and Anna Olsson and Kerstin Nordin-Henriksson for their contribution to athb7-athb12 transgenic lines.
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