Upregulation of an Arabidopsis RING‐H2 gene, XERICO, confers drought tolerance through increased abscisic acid biosynthesis

Abstract

Summary RING (really interesting new gene) zinc-finger proteins have important regulatory roles in the development of a variety of organisms. The XERICO gene encodes a small protein (162 amino acids) with an N-terminal transmembrane domain and a RING-H2 zinc-finger motif located at the C-terminus. In silico gene-expression analysis indicated that XERICO is induced by salt and osmotic stress. Compared with wild-type (WT) Arabidopsis plants, transgenic plants overexpressing XERICO (35S::XERICO) exhibited hypersensitivity to salt and osmotic stress and exogenous abscisic acid (ABA) during germination and early seedling growth. When subjected to a drought treatment, transcriptional upregulation of a key ABA-biosynthesis gene, AtNCED3, was much faster and stronger in 35S::XERICO plants compared with WT plants. Further, upregulation of XERICO substantially increased cellular ABA levels. The adult 35S::XERICO plants, in contrast to early seedling growth, showed a marked increase in their tolerance to drought stress. Yeast two-hybrid screening indicated that XERICO interacts with an E2 ubiquitin-conjugating enzyme (AtUBC8) and ASK1-interacting F-box protein (AtTLP9), which is involved in the ABA-signaling pathway. Affymetrix GeneChip array analysis showed that the expressions of many of the genes involved in the biosynthesis of plant hormones (e.g. ethylene, brassinosteroid, gibberellic acid) were significantly changed in the 35S::XERICO plants. These results suggest that the homeostasis of various plant hormones might be altered in 35S::XERICO plants, possibly by overaccumulation of ABA.

SOMNUS, a CCCH-Type Zinc Finger Protein inArabidopsis, Negatively Regulates Light-Dependent Seed Germination Downstream of PIL5

“…DELLA proteins are nucleus-localized negative GA signaling components that inhibit various GA responses, including seed germination, stem elongation, and floral development (Peng et al, 1997(Peng et al, , 1999Silverstone et al, 1998;Ikeda et al, 2001;Sun and Gubler, 2004;Tyler et al, 2004). The molecular functions of DELLA proteins are not clearly defined, but a recent report shows that one DELLA protein binds directly to DNA and regulates the expression of various genes, including GA receptor genes (GID1a and -1b), GA anabolic genes (GA20ox2 and GA3ox1), and XERICO, which encodes a ring finger ubiquitin E3 ligase that activates ABA biosynthesis (Ko et al, 2006;Zentella et al, 2007). There are five DELLA proteins in Arabidopsis (GA-INSENSITIVE [GAI], RGA, RGA LIKE1 [ RGL1], RGL2, and RGL3), which have shared but distinct roles in mediating different GA responses.…”

Global Analysis of DELLA Direct Targets in Early Gibberellin Signaling inArabidopsis

“…XERICO, a GA-repressed gene, plays a role in regulating ABA accumulation (Ko et al, 2006). In addition, the BR6ox2 (Brassinosteroid-6-oxidase2) gene, which was downregulated by GA, encodes a cytochrome p450 enzyme (CYP85A2) that catalyzes the last step in brassinosteroid (BR) biosynthesis (Shimada et al, 2003;Nomura et al, 2005).…”

“…XERICO was named for the drought tolerance phenotype of overexpression of this gene using the CaMV35S promoter in Arabidopsis (Ko et al, 2006). This drought tolerance phenotype is accompanied by an elevated level of ABA in the plant and hypersensitivity to salt and ABA during seedling growth.…”

Interactions between theS-Domain Receptor Kinases and AtPUB-ARM E3 Ubiquitin Ligases Suggest a Conserved Signaling Pathway in Arabidopsis

“…ATL43 has been proposed to function as a positive regulator of ABA responses because atl43 mutant T-DNA lines were moderately insensitive at high concentration of ABA during germination (Serrano et al, 2006). Increased expression of XERICO was found to increase endogenous ABA levels and XERICO was thought to regulate the expression of an ABA biosynthesis gene (Ko et al, 2006). Finally, overexpression of the U-box E3 ligase, AtCHIP, was found to cause increased sensitivity to ABA treatment (Luo et al, 2006).…”