Characterization of OsbZIP23 as a Key Player of the Basic Leucine Zipper Transcription Factor Family for Conferring Abscisic Acid Sensitivity and Salinity and Drought Tolerance in Rice  

Abstract

OsbZIP23 is a member of the basic leucine zipper (bZIP) transcription factor family in rice (Oryza sativa). Expression of OsbZIP23 is strongly induced by a wide spectrum of stresses, including drought, salt, abscisic acid (ABA), and polyethylene glycol treatments, while other stress-responsive genes of this family are slightly induced only by one or two of the stresses. Transactivation assay in yeast demonstrated that OsbZIP23 functions as a transcriptional activator, and the sequences at the N terminus (amino acids 1-59) and a region close to the C terminus (amino acids 210-240) are required for the transactivation activity. Transient expression of OsbZIP23-green fluorescent protein in onion (Allium cepa) cells revealed a nuclear localization of the protein. Transgenic rice overexpressing OsbZIP23 showed significantly improved tolerance to drought and high-salinity stresses and sensitivity to ABA. On the other hand, a null mutant of this gene showed significantly decreased sensitivity to a high concentration of ABA and decreased tolerance to high-salinity and drought stress, and this phenotype can be complemented by transforming the OsbZIP23 back into the mutant. GeneChip and real-time polymerase chain reaction analyses revealed that hundreds of genes were up-or down-regulated in the rice plants overexpressing OsbZIP23. More than half of these genes have been annotated or evidenced for their diverse functions in stress response or tolerance. In addition, more than 30 genes that are possible OsbZIP23-specific target genes were identified based on the comparison of the expression profiles in the overexpressor and the mutant of OsbZIP23. Collectively, these results indicate that OsbZIP23 functions as a transcriptional regulator that can regulate the expression of a wide spectrum of stress-related genes in response to abiotic stresses through an ABA-dependent regulation pathway. We propose that OsbZIP23 is a major player of the bZIP family in rice for conferring ABA-dependent drought and salinity tolerance and has high potential usefulness in genetic improvement of stress tolerance.

SALT-RESPONSIVE ERF1 Regulates Reactive Oxygen Species-Dependent Signaling during the Initial Response to Salt Stress in Rice

“…Rice seedlings overexpressing ZFP179 possess enhanced expression of DREB2A, which acts ABA-independently (Dubouzet et al, 2003). Furthermore, overexpression of bZIP23, ZFP179, and ZFP252, genes that did not respond to salt stress in serf1 roots (Figure 4), increases expression of LEA3 (Xiang et al, 2008;Xu et al, 2008;Sun et al, 2010). Although LEA3 expression is ABA dependent, it is affected by the impaired H 2 O 2 signaling in serf1, probably due to the lack of response(s) of upstream regulator(s).…”

A STRESS-RESPONSIVE NAC1-Regulated Protein Phosphatase Gene RiceProtein Phosphatase18Modulates Drought and Oxidative Stress Tolerance through Abscisic Acid-Independent Reactive Oxygen Species Scavenging in Rice

“…8B). To further exclude the possibility of OsPP18 on ABA signaling, the expression of a few well-known ABA-responsive genes in rice, including RESPONSIVE TO ABA PROTEIN21 (RAB21), LOW TEMPERATURE INDUCED PROTEIN9 (LIP9), and Osb-ZIP23 (Mundy and Chua, 1988;Rabbani et al, 2003;Xiang et al, 2008), was checked in the ospp18 mutant. The qPCR results indicated that the ABA-induced expression of these genes was not affected in the ospp18 mutant (Fig.…”

Constitutive Activation of Transcription Factor OsbZIP46 Improves Drought Tolerance in Rice

“…OsABI5, named according to its homology to ABI5 in Arabidopsis, was suggested to be involved in ABA signal transduction and stress responses (Zou et al, 2007(Zou et al, , 2008. OsbZIP23 was characterized as a key player of the bZIP family for conferring ABA sensitivity, salinity, and drought tolerance of rice (Xiang et al, 2008). Several other members were also mentioned for their involvement in ABA and stress (Zou et al, 2007;Lu et al, 2009;Amir Hossain et al, 2010).…”

“…Several members have been studied for their functions potentially related to stress responses, such as LIP19 (Shimizu et al, 2005), OsBZ8 (Nakagawa et al, 1996;Mukherjee et al, 2006), and RF2a and RF2b (Dai et al, 2004(Dai et al, , 2008. Noticeably, in contrast to the comprehensive studies of ABFs in Arabidopsis, mainly three members of the third subfamily in rice, TRAB1, OsABI5, and OsbZIP23, have been studied for their roles in ABA-mediated stress responses (Hobo et al, 1999;Xiang et al, 2008;Zou et al, 2008). TRAB1, which is identified by yeast two-hybrid screening for proteins that interact with the seed development-related transcription factor VP1, can be activated by ABA-dependent phosphorylation in its Ser-102 residue (Hobo et al, 1999;Kagaya et al, 2002;Kobayashi et al, 2005), but its biologic function remains to be clarified.…”