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Low temperature affects plant growth and crop productivity. The CBF genes are a class of transcription factors that play important roles in cold response. Here we report that AtMYB14 participates in freezing tolerance in Arabidopsis by affecting expression of CBF genes. The AtMYB14 gene was down-regulated by cold treatment. AtMYB14 encodes a nuclear protein that functions as an R2R3-MYB transcription activator. Knock-down of AtMYB14 by artificial microRNA increased the tolerance to freezing stress. Both the CBF genes and the downstream genes were induced to a much higher level in AtMYB14 knock-down plants than in wild type under cold treatment. Our results suggest that AtMYB14 plays an important role in the plant response to cold stress. [ABSTRACT FROM AUTHOR]

Abstract: Soil salinity significantly limits plant productivity on agricultural lands, and salt tolerance of plant requires a complex mechanism in which many genes are involved. From an activation-tagging mutant collection, we identified a loss-of-function Arabidopsis mutant which exhibits hypersensitivity to NaCl during seed germination and is designated ssg1 (salt sensitive during seed germination 1). Knocking down the expression of SSG1 by RNAi recapitulated the phenotype of ssg1, suggesting that functional SSG1 is necessary for normal seed germination in the presence of NaCl. The seed germination of ssg1 was not sensitive to K+, but was hypersensitive to osmotic stress. SSG1 encodes a protein kinase, possibly with alternatively spliced forms. In vitro kinase assay indicated that SSG1 possessed protein kinase activity which can both auto-phosphorylate and phosphorylate substrate. Quantitative real-time RT-PCR analysis showed that, in the mutants ssg1-1 and ssg1-2, the expression level of some salt-responsive marker genes, i.e., SOS1, SOS2, SOS3, SOS4, AtNHX and AtNKT, was down-regulated, whereas SSG1 expression level was not changed in sos mutants. These results suggest that SSG1 is possibly a component in the signaling pathway in response of plants to salt stress. [Copyright &y& Elsevier]

Ethylene plays a crucial role in plant resistance to necrotrophic pathogens, in which ETHYLENE RESPONSE FACTORs (ERFs) are often involved., Here, we evaluated the role of an ERF transcription factor, RELATED TO AP2 2 (RAP2.2), in Botrytis resistance and ethylene responses in Arabidopsis. We analyzed the resistance of transgenic plants overexpressing RAP2.2 and the T-DNA insertion mutant to Botrytis cinerea. We assessed its role in the ethylene signaling pathway by molecular and genetic approaches., RAP2.2-overexpressing transgenic plants showed increased resistance to B. cinerea, whereas its T-DNA insertion mutant rap2.2-3 showed decreased resistance. Overexpression of RAP2.2 in ethylene insensitive 2 ( ein2) and ein3 ein3-like 1 ( eil1) mutants restored their resistance to B. cinerea. Both ethylene and Botrytis infection induced the expression of RAP2.2 and the induction was disrupted in ein2 and ein3 eil1 mutants. We identified rap2.12-1 as a T-DNA insertion mutant of RAP2.12, the closest homolog of RAP2.2. The hypocotyls of rap2.2-3 rap2.12-1 double mutants showed ethylene insensitivity. The constitutive triple response in constitutive triple response1 ( ctr1) was partially released in the rap2.2-3 rap2.12-1 ctr1 triple mutants., Our findings demonstrate that RAP2.2 functions as an important regulator in Botrytis resistance and ethylene responses. [ABSTRACT FROM AUTHOR]

Summary The anaphase-promoting complex/cyclosome (APC/C) is an E3 ubiquitin ligase that is involved in regulating cell-cycle progression. It has been widely studied in yeast and animal cells, but the function and regulation of the APC/C in plant cells are largely unknown. The Arabidopsis APC/C comprises at least 11 subunits, only a few of which have been studied in detail. APC4 is proposed to be a connector in the APC/C in yeast and animals. Here, we report the functional characterization of the Arabidopsis APC4 protein. We examined three heterozygous plant lines carrying apc4 alleles. These plants showed pleiotropic developmental defects in reproductive processes, including abnormal nuclear behavior in the developing embryo sac and aberrant cell division in embryos; these phenotypes differ from those reported for mutants of other subunits. Some ovules and embryos of apc4/ + plants also accumulated cyclin B protein, a known substrate of APC/C, suggesting a compromised function of APC/C. Arabidopsis APC4 was expressed in meristematic cells of seedlings, ovules in pistils and embryos in siliques, and was mainly localized in the nucleus. Additionally, the distribution of auxin was distorted in some embryos of apc4/ + plants. Our results indicate that Arabidopsis APC4 plays critical roles in female gametogenesis and embryogenesis, possibly as a connector in APC/C, and that regulation of auxin distribution may be involved in these processes. [ABSTRACT FROM AUTHOR]

In plants, the meristem has to maintain a separate population of pluripotent cells that serve two main tasks, i.e., self‐maintenance and organ initiation, which are separated spatially in meristem. Prior to our study, WUS and WUS‐like WOX genes had been reported as essential for the development of the SAM. In this study, the consequences of gain of WOX1 function are described. Here we report the identification of an Arabidopsis gain‐of‐function mutant wox1‐D, in which the expression level of the WOX1 (WUSCHEL HOMEOBOX 1) was elevated and subtle defects in meristem development were observed. The wox1‐D mutant phenotype is dwarfed and slightly bushy, with a smaller shoot apex. The wox1‐D mutant also produced small and dark green leaves, and exhibited a failure in anther dehiscence and male sterility. Molecular evidences showed that the transcription of the stem cell marker gene CLV3 was down‐regulated in the meristem of wox1‐D but accumulated in the other regions, i.e., in the root‐hypocotyl junction and at the sites for lateral root initiation. The fact that the organ size and cell size in leaves of wox1‐D are smaller than those in wild type suggests that cell expansion is possibly affected in order to have partially retarded the development of lateral organs, possibly through alteration of CLV3 expression pattern in the meristem. An S‐adenosylmethionine decarboxylase (SAMDC) protein, SAMDC1, was found able to interact with WOX1 by yeast two‐hybrid and pull‐down assays in vitro. HPLC analysis revealed a significant reduction of polyamine content in wox1‐D. Our results suggest that WOX1 plays an important role in meristem development in Arabidopsis, possibly via regulation of SAMDC activity and polyamine homeostasis, and/or by regulating CLV3 expression. [ABSTRACT FROM AUTHOR]

Abstract: Lead (Pb) is one of the main sources of pollution in the environment, and is severely toxic to plants and animals. Using a DNA microarray, the transcriptional profiles of Arabidopsis thaliana genes in response to Pb treatment were investigated under different concentrations of Pb(NO3)2 solution from low (1μM, 10μM) to high (100μM) during the early stages of toxicity (3h and 24h). At each time point, Pb content was measured to confirm that the extensive heavy metal accumulation in Arabidopsis seedlings was caused by Pb treatment. Furthermore, eighteen selected genes with either moderate or high differential expression values from the microarray analysis were independently analyzed by quantitative real-time RT-PCR to confirm the reliability of the data. In our microarray analysis, the expressions of over 1310 genes were identified in response to Pb treatment. Extensive hierarchical clustering analysis of these responses indicated that the major consistently activated genes were also involved in common stress-induced responses. Especially, those that have been previously reported to be heavy metal inducible genes were significantly induced by lead treatment. Moreover, some important genes encoding enzymes or proteins involved in sulfur assimilation, GSH metabolism, indole-3-acedic acid (IAA) and jasmonic acid (JA) biosynthesis were activated, and these pathways were linked, directly or indirectly through signaling pathways, to biosynthesis of metal transports and detoxification molecules. Taken together, our results provided a new insight into the molecular mechanism of lead detoxification in Arabidopsis, and facilitated an understanding of the general lead/heavy metal-adaptive mechanism undertaken by plants. [Copyright &y& Elsevier]

Arabidopsis AtMRB1 is predicted to encode a novel protein of 432 amino acid residues in length, with four putative trans-membrane domains. In the present study, characterization of AtMRB1 is conducted. Green fluorescent protein (GFP) fusion protein assay showed that AtMRB1 was located in the plasma membrane. Transgenic lines overexpressing AtMRB1 driven by a CaMV 35S promoter were generated. Statistic analysis showed that, during the seedling stage, the organ sizes of the transgenic lines including hypocotyl length, root length and root weight were significantly larger than those of the wild type plants under both light and dark conditions. In the adult plant stage, the AtMRB1 overexpressor plants were found to have larger organ sizes in terms of leaf length and width, and increased number of cauline leaves and branches when bolting. Further observation indicated that the larger leaf size phenotype was due to a larger number of mesophyll cells, the size of which was not altered. Quantitative real-time polymerase chain reaction analysis showed that the transcription of ANT, ROT3 and GRF5 were upregulated in the AtMRB1-overexpressor plants. These data suggest that AtMRB1 is possibly a positive regulator of organ size development in Arabidopsis, mainly through cell number control. [ABSTRACT FROM AUTHOR]

Large collections of insertional Arabidopsis lines are valuable for research on functional genomics. Using the activation tagging vector pSKI015, more than 45 000 T-DNA insertion lines were generated by Agrobacterium-mediated floral-dip transformation protocol. 2304 insertion lines were analyzed and 1502 items of plant sequences flanking the T-DNA insertion sites were obtained by a modified thermal asymmetric interlaced PCR (TAIL-PCR) protocol. These sequences were searched against Genebank database using blast and 1194 insertion sites were determined according to the sequences matching to the Arabidopsis genome sequence. The insertion sites were distributed on all the five Arabidopsis chromosomes and the interfered genes were classified into 14 function categories. Analysis on 1194 items of 100-bp sequences surrounding T-DNA insertion sites showed that 27 and 31% GC contents were likely to favor the T-DNA integration. Sixty-eight items of these 100-bp sequences having more than two insertions were chosen to look for motifs in favor of T-DNA integration. The results showed that “ATNTT” (N represents A/T/C/G) and the polyT and polyA motifs probably play a role in the T-DNA integration event. [Copyright &y& Elsevier]