The Arabidopsis homeobox gene ATHB‐7 is induced by water deficit and by abscisic acid

Abstract

Homeodomain-leucine zipper (HD-Zip) proteins are putative transcription factors encoded by a class of recently discovered homeobox genes as yet found only in plants. This paper reports on the characterization of one of these genes, ATHB-7, in Arabidopsis thaliana. ATHB-7 transcripts were present in all organs of the plant at low levels, but expression was induced several-fold by water deficit, osmotic stress as well as by exogenous treatment with abscisic acid (ABA), a response being detectable at 10(-8) M and reaching a maximum at 10(-6) M ABA. The ATHB-7 transcript was detected within 30 min after treatment with ABA and the transcript level was rapidly reduced after removal of the hormone. The induction of ATHB-7 was shown to be mediated strictly via ABA, since no induction of ATHB-7 was detectable in the ABA-deficient mutant aba-3 subjected to drought treatment. Induction levels in two ABA-insensitive mutants abi2 and abi3 were similar to the wild-type response. In the abi1 mutant, however, induction was impaired as 100-fold higher concentrations of ABA were required for a maximum induction as compared with wild-type. In this mutant the ATHB-7 response was reduced also after drought and osmotic stress treatments. These results indicate that ATHB-7 is transcriptionally regulated in an ABA-dependent manner and may act in a signal transduction pathway which mediates a drought response and also includes ABI1.

Linking the Salt Transcriptome with Physiological Responses of a Salt-Resistant Populus Species as a Strategy to Identify Genes Important for Stress Acclimation

“…Salt exposure generally leads to increased abscisic acid levels, but in Euphrat poplar more rapidly than in salt-sensitive poplar species (Chen et al, 2001;Luo et al, 2009). Here, activation of a putative homeodomain transcription factor (homolog to ATHB-7) and aldehyde dehydrogenase was observed, which are known to be regulated by abscisic acid and to be responsive to salinity and drought (Sö derman et al, 1996;Seki et al, 2002;Olsson et al, 2004;Sunkar et al, 2003;Kotchoni et al, 2006). The late response of these genes, which occurred only when the leaves were exposed to a high salt level, suggests that they are necessary to afford tissue protection from excessive ion accumulation or high osmotic pressure.…”

The Arabidopsis ABSCISIC ACID-INSENSITIVE2 (ABI2) and ABI1 genes encode homologous protein phosphatases 2C involved in abscisic acid signal transduction.

“…Nevertheless, the ABA-dependent accumulation of this same transcript triggered by progressive drought in the roots of adult plants is severely inhibited in abil-7 but not in abi2-7 (Gosti et al, 1995). Additional adaptive responses, such as root morphogenesis (drought rhizogenesis; Vartanian et al, 1994) as well as accumulations of the AfDi27 (Gosti et al, 1995) and ATHB-7 (Soderman et al, 1996) transcripts provoked by water stress, are affected in abi7-7 but not in abi2-7. Conversely, inductions of the Adh transcript by water stress and by exogenous ABA are affected in abi2-7 but not in abi7-7 (de Bruxelles et al, 1996).…”

“…However, induction of the Adb transcript by ABA and drought stress is severely inhibited inabi2-7 and not in abil-7 (de Bruxelles et al, 1996). Conversely, drought rhizogenesis (Vartanian et al, 1994), induction of the ATHB-7 transcript by water stress (Soderman et al, 1996), as well as the induction of several coldresponsive COR genes by exogenous ABA (Gilmour and Thomashow, 1991) are affected in abil-7 but not in abi2-7. Also, inductions of the ABI7 and AB12 transcripts themselves by applied ABA are inhibited in abil-7 and abi2-7, suggesting that in the simplest scheme, both proteins may impinge on the effector(s) that participates in an autoregulatory circuit required to maintain proper levels of the two ABI transcripts.…”

“…They affect both seeds and vegetative tissues, suggesting that their gene products act in ABA signal transduction before major branch points that control tissue-specific cascades. Differential effects imparted by the abi7-7 and abi2-7 mutations are most evident in adaptive responses to drought by modifications of the root, a process known as drought rhizogenesis (Vartanian et al, 1994), and induction of certain genes (Gilmour and Thomashow, 1991;Gosti et al, 1995;de Bruxelles et al, 1996;Soderman et al, 1996). Nevertheless, these mutants also have several phenotypes in common.…”

A coumaroyl-ester-3-hydroxylase Insertion Mutant Reveals the Existence of Nonredundant meta-Hydroxylation Pathways and Essential Roles for Phenolic Precursors in Cell Expansion and Plant Growth

“…These include the gene responsive to dehydration 22 (RD22I, At5g25610), which is strongly induced by abscisic acid and drought (YamaguchiShinozaki and Shinozaki, 1993), and the Arg decarboxylase 2 (ADC2, At4g34710) gene, which is strongly activated by abscisic acid, but also by methyl jasmonate and mechanical wounding, and is involved in polyamine biosynthesis (Perez-Amador et al, 2002). Also expressed to higher levels in cyp98A3 insertion mutants were two homeodomain Leu-zipper transcription factors (ATHB5, At5g65310; and ATHB7, At2g46680) involved in abscisic acid-mediated signaling pathways related to drought and osmotic stress (Sö derman et al, 1996) and seed germination (Johannesson et al, 2003), respectively.…”