The homeobox genes ATHB12 and ATHB7encode potential regulators of growth in response to water deficit in Arabidopsis

Abstract

The Arabidopsis thaliana homeodomain leucine-zipper gene ATHB7 , which is active specifically under water deficit conditions, is proposed to act as a negative regulator of growth (Soderman et al ., 1996, Plant J. 10: 375 381; Hjellstrom et al ., 2003, Plant Cell Environ 26: 1127 1136). In this report we demonstrate that the paralogous gene, ATHB12 , has a similar expression pattern and function. ATHB12 ,like ATHB7 ,was up-regulated during water deficit conditions, the up-regulation being dependent on abscisic acid (ABA) and on the activity of the Ser/Thr phosphatases ABI1 and ABI2. Plants that are mutant for ATHB12 , as a result of T-DNA insertions in the ATHB12 gene, showed a reduced sensitivity to ABA in root elongation assays, whereas transgenic Arabidopsis plants expressing ATHB12 and/or ATHB7 as driven by the CaMV 35S promoter were hypersensitive in this response compared to wild-type. High-level expression of either gene also resulted in a delay in inflorescence stem elongation growth and caused plants to develop rosette leaves with a more rounded shape, shorter petioles, and increased branching of the inflorescence stem. Transgenic Arabidopsis plants expressing the reporter gene uidA under the control of the ATHB12 promoter showed marker gene activity in axillary shoot primordia, lateral root primordia, inflorescence stems and in flower organs. Treatment of plants with ABA or water deficit conditions caused the activity of ATHB12 to increase in the inflorescence stem, the flower organs and the leaves, and to expand into the vasculature of roots and the differentiation/elongation zone of root tips. Taken together, these results indicate that ATHB12 and ATHB7 act to mediate a growth response to water deficit by similar mechanisms.

Seed-Specific Expression of a Feedback-Insensitive Form of CYSTATHIONINE-γ-SYNTHASE in Arabidopsis Stimulates Metabolic and Transcriptomic Responses Associated with Desiccation Stress

“…Finally, two HOMEOBOX proteins, HB12 (At3g61890) and HB7 (At2g46680), were upregulated significantly (Table I). These two genes were reported previously to encode potential regulators of growth in response to water deficit (Olsson et al, 2004).…”

ATHB17 Is a Positive Regulator of Abscisic Acid Response during Early Seedling Growth

“…ATHB6, which was isolated as an ABI1-interacting protein, negatively regulate the ABA response during germination and stomatal closure (Himmelbach et al, 2002;Lechner et al, 2011). ATHB7 and ATHB12 are positive regulators of ABA inhibition of root and stem growth (Olsson et al, 2004). Recently, it has been demonstrated that ATHB12 inhibits stem growth by reducing GA20 oxidase (Son et al, 2010).…”

“…On the other hand, the HD-Zip I subfamily is composed of 17 members, and many of them are known to modulate plant growth in response to developmental and environmental cues (Harris et al, 2011;Henriksson et al, 2005). For instance, ATHB7, ATHB12, and ATHB13 affect plant growth under abiotic stress conditions (Olsson et al, 2004;Son et al, 2010). ATHB6, ATHB5, and ATHB20 are regulators of a subset of ABA response (Barrero et al, 2010;Himmelbach et al, 2002;Johannesson et al, 2003).…”

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.…”