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

Abstract

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.

Rice HOX12 Regulates Panicle Exsertion by Directly Modulating the Expression of ELONGATED UPPERMOST INTERNODE1

“…There are 14 putative HD-ZIP I genes in the rice genome. An interesting point raised by Valdés et al (2012) is that HD-ZIP genes that share targets but have different expression patterns or different reactions to specific external conditions may play similar roles in modulating ABA signal perception. The data regarding the expression of HD-ZIP I HOXs in rice through different developmental stages obtained from the Rice Expression Profile Database (RiceXPro) show that different HD-ZIP I genes have different During the reproductive stage, GA 4 accumulates in the panicle.…”

“…Members of HD-ZIP I increase plant plasticity by mediating external signals and regulating growth in response to environmental conditions (Wang et al, 2003;Lin et al, 2008;Manavella et al, 2008;Brandt et al, 2014;Chang et al, 2014;Zhao et al, 2014;Capella et al, 2015). For example, Arabidopsis HB7 and HB12 encode potential regulators of growth in response to water deficit (Olsson et al, 2004;Valdés et al, 2012). HB6 is a target of phosphatase ABI1 and regulates hormone responses (Himmelbach et al, 2002).…”

Leaf Growth Response to Mild Drought: Natural Variation in Arabidopsis Sheds Light on Trait Architecture

“…Within the 283-gene set were 11 "core" genes that showed very similar transcriptional responses in almost all accessions for their response to mild drought, suggesting that they play a pivotal role in the mild drought response. Three of these 11 genes encode proteins that mediate ABA responses: ABI FIVE BINDING PROTEIN1 (AFP1), HOMEOBOX7 (HB7), and PROTEIN PHOSPHATASE 2CA (AHG3/PP2CA) (Garcia et al, 2008;Rodrigues et al, 2013;Olsson et al, 2004), of which HB7 is known to be involved in the response of leaf growth to drought (Ré et al, 2014;Valdés et al, 2012;Olsson et al, 2004). Two other core genes encode EXPANSIN A 15 (EXPA15) and BETA-D-XYLOSIDASE4 (XYL4), both cell wall modifiers involved in growth responses.…”

PHABULOSA Mediates an Auxin Signaling Loop to Regulate Vascular Patterning in Arabidopsis

“…ChIP was performed following Bowler et al (2004) as detailed previously by Valdés et al (2012). Briefly, 9-d-old seedlings from pPHB::PHBd:GFP transgenic plants were cross-linked with formaldehyde at 1% (v/v), and nuclei were extracted.…”