The plasma membrane H + -ATPase (PM H + -ATPase) plays an important role in the regulation of ion and metabolite transport and is involved in physiological processes that include cell growth, intracellular pH, and stomatal regulation. PM H + -ATPase activity is controlled by many factors, including hormones, calcium, light, and environmental stresses like increased soil salinity. We have previously shown that the Arabidopsis thaliana Salt Overly Sensitive2-Like Protein Kinase5 (PKS5) negatively regulates the PM H + -ATPase. Here, we report that a chaperone, J3 (DnaJ homolog 3; heat shock protein 40-like), activates PM H + -ATPase activity by physically interacting with and repressing PKS5 kinase activity. Plants lacking J3 are hypersensitive to salt at high external pH and exhibit decreased PM H + -ATPase activity. J3 functions upstream of PKS5 as double mutants generated using j3-1 and several pks5 mutant alleles with altered kinase activity have levels of PM H + -ATPase activity and responses to salt at alkaline pH similar to their corresponding pks5 mutant. Taken together, our results demonstrate that regulation of PM H + -ATPase activity by J3 takes place via inactivation of the PKS5 kinase.

We report that the Arabidopsis thaliana mutant sensitive to ABA and drought2 (sad2), which harbors a T-DNA insertion in an importin b-like gene, is more tolerant to UV-B radiation than the wild type. Analysis of cyclobutane pyrimidine dimer accumulation revealed that less DNA damage occurred in sad2 than in the wild type during UV-B treatment. No significant growth difference was observed between sad2 and the wild type when treated with the genotoxic drug methyl methanesulfonate, suggesting that SAD2 functions in UV-B protection rather than in DNA damage repair. Whereas the R2R3-type transcription repressor MYB4 has previously been shown to negatively regulate the transcription of cinnamate 4-hydroxylase (C4H) and thus to regulate the synthesis of sinapate esters, expression of both MYB4 and C4H and accumulation of UVabsorbing compounds were significantly higher in sad2 than in the wild type. MYB4 did not localize to the nucleus in the sad2 mutant, suggesting that SAD2 is required for MYB4 nuclear trafficking. SAD2 and MYB4 coimmunoprecipitated, indicating that these proteins localize in the same complex in vivo. MYB4 protein specifically bound to its own promoter in gel shift assays and repressed its own expression, demonstrating that MYB4 protein and mRNA are part of a negative autoregulatory loop. This feedback loop is altered in the sad2 mutant due to the absence of MYB4 protein in the nucleus, leading to the constitutive expression of MYB4 and C4H and resulting in accumulation of UV-absorbing pigments that shield the plant from UV-B radiation.

The Salt Overly Sensitive (SOS) pathway regulates intracellular sodium ion (Na+) homeostasis and salt tolerance in plants. Until recently, little was known about the mechanisms that inhibit the SOS pathway when plants are grown in the absence of salt stress. In this study, we report that the Arabidopsis thaliana 14-3-3 proteins λ and κ interact with SOS2 and repress its kinase activity. Growth in the presence of salt decreases the interaction between SOS2 and the 14-3-3 proteins, leading to kinase activation in planta. 14-3-3 λ interacts with the SOS2 junction domain, which is important for its kinase activity. A phosphorylation site (Ser-294) is identified within this domain by mass spectrometry. Mutation of Ser-294 to Ala or Asp does not affect SOS2 kinase activity in the absence of the 14-3-3 proteins. However, in the presence of 14-3-3 proteins, the inhibition of SOS2 activity is decreased by the Ser-to-Ala mutation and enhanced by the Ser-to-Asp exchange. These results identify 14-3-3 λ and κ as important regulators of salt tolerance. The inhibition of SOS2 mediated by the binding of 14-3-3 proteins represents a novel mechanism that confers basal repression of the SOS pathway in the absence of salt stress.

The SnRK2 gene family is a group of plant-specific protein kinases that has been implicated in ABA and abiotic stress signaling. We found 11 SnRK2s in maize, assigned names from ZmSnRK2.1 to ZmSnRK2.11 and cloned ten of them. By analyzing the gene structure of all the SnRK2s from Arabidopsis, rice, and maize, we found seven exons that were conserved in length among most of the SnRK2s. Although the C-terminus was divergent, we found seven conserved motifs. Of these, motif 1 was common to all of the SnRK2 genes. Based on phylogenetic analysis using the kinase domain and motif 1, the SnRK2s were divided into three groups. Motifs 4 and 5 were found specifically in group I, and many genes of this group have been confirmed to be induced by ABA. This result suggests that these two motifs mediate the ABA response. The expression patterns of ZmSnRK2 genes were characterized by using quantitative real-time RCR, which revealed that ZmSnRK2 genes were induced by one or more abiotic stress treatments and therefore may play important roles in maize stress responses.

As a cause of community-acquired infections, extended-spectrum β-lactamase (ESBL)-producing Escherichia coli constitute an emerging public-health concern. Few data on the molecular epidemiology of ESBL-producing E. coli isolates from pets are available in China. Detection and characterization of ESBL genes (bla(CTX-M), bla(SHV) and bla(TEM)) was conducted among 240 E. coli isolates recovered from healthy and sick pets in South China from 2007 to 2008. The clonal relatedness of ESBL-producing E. coli isolates was assessed by pulsed field gel electrophoresis. ESBL-encoding genes were identified in 97 (40.4%) of the 240 isolates and 96 (40.0%) of them harbored CTX-M. The most common CTX-M types were CTX-M-14 (n = 45) and CTX-M-55 (n = 24). The recently reported CTX-M-64 was identified in three isolates. Isolates producing CTX-M-27, -15, -65, -24, -3 and -9 were also identified. Ten isolates carried two or three CTX-M types, with the combination of CTX-M-14 and CTX-M-55 being the most frequent (n = 6). ISEcp1 was identified in the upstream region of 93 out of the 107 bla(CTX-M) genes (86.9%). The sequence of the spacer region (45 bp) between ISEcp1 and the start codon of all bla(CTX-M-55) genes (except four) was identical to that of bla(CTX-M-64). No major clonal relatedness was observed among these CTX-M producers. It is suggested that the horizontal transfer of bla(CTX-M) genes, mediated by mobile elements, contributes to their dissemination among E. coli isolates from pets. Our finding of high prevalence of ESBL in E. coli of companion animal origin illustrates the importance of molecular surveillance in tracking CTX-M-producing E. coli strains in pets.

SUMMARYArabidopsis gain-of-resistance mutants, which show HR-like lesion formation and SAR-like constitutive defense responses, were used well as tools to unravel the plant defense mechanisms. We have identified a novel mutant, designated constitutive expresser of PR genes 30 (cpr30), that exhibited dwarf morphology, constitutive resistance to the bacterial pathogen Pseudomonas syringae and the dramatic induction of defense-response gene expression. The cpr30-conferred growth defect morphology and defense responses are dependent on ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), PHYTOALEXIN DEFICIENT 4 (PAD4), and NONRACE-SPECIFIC DISEASE RESISTANCE 1 (NDR1). Further studies demonstrated that salicylic acid (SA) could partially account for the cpr30-conferred constitutive PR1 gene expression, but not for the growth defect, and that the cpr30-conferred defense responses were NPR1 independent. We observed a widespread expression of CPR30 throughout the plant, and a localization of CPR30-GFP fusion protein in the cytoplasm and nucleus. As an F-box protein, CPR30 could interact with multiple Arabidopsis-SKP1-like (ASK) proteins in vivo. Co-localization of CPR30 and ASK1 or ASK2 was observed in Arabidopsis protoplasts. Based on these results, we conclude that CPR30, a novel negative regulator, regulates both SA-dependent and SA-independent defense signaling, most likely through the ubiquitin-proteasome pathway in Arabidopsis.

Microfilament dynamics play a critical role in regulating stomatal movement; however, the molecular mechanism underlying this process is not well understood. We report here the identification and characterization of STOMATAL CLOSURE-RELATED ACTIN BINDING PROTEIN1 (SCAB1), an Arabidopsis thaliana actin binding protein. Plants lacking SCAB1 were hypersensitive to drought stress and exhibited reduced abscisic acid-, H 2 O 2 -, and CaCl 2 -regulated stomatal movement. In vitro and in vivo analyses revealed that SCAB1 binds, stabilizes, and bundles actin filaments. SCAB1 shares sequence similarity only with plant proteins and contains a previously undiscovered actin binding domain. During stomatal closure, actin filaments switched from a radial orientation in open stomata to a longitudinal orientation in closed stomata. This switch took longer in scab1 plants than in wild-type plants and was correlated with the delay in stomatal closure seen in scab1 mutants in response to drought stress. Our results suggest that SCAB1 is required for the precise regulation of actin filament reorganization during stomatal closure.

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