Molecular characterization of an AtPYL1-like protein, BrPYL1, as a putative ABA receptor in Brassica rapa.

Abscisic acid (ABA)-induced physiological changes are conserved in many land plants and underlie their responses to environmental stress and pathogens. The PYRABACTIN RESISTANCE1/PYR1-LIKE/REGULATORY COMPONENTS OF ABA RECEPTORS (PYLs)-type receptors perceive the ABA signal and initiate signal transduction. Here, we show that the genome of Brassica rapa encodes 24 putative AtPYL-like proteins. The AtPYL-like proteins in Brassica rapa (BrPYLs) can also be classified into 3 subclasses. We found that nearly all BrPYLs displayed high expression in at least one tissue. Overexpression of BrPYL1 conferred ABA hypersensitivity to Arabidopsis. Further, ABA activated the expression of an ABA-responsive reporter in Arabidopsis protoplasts expressing BrPYL1. Overall, these results suggest that BrPYL1 is a putative functional ABA receptor in Brassica rapa.

Propioniciclava sinopodophylli sp. nov., isolated from leaves of Sinopodophyllum hexandrum (Royle) Ying.

A Gram-reaction-positive, facultatively anaerobic, rod-shaped and non-motile bacterial strain, designated TEYR-7T, was isolated from the leaves of Sinopodophyllum hexandrum collected from the Qinling Mountains in Shaanxi Province, northwest China. Growth of strain TEYR-7T occurred at 15-37 °C (optimum, 28-30 °C), at pH 6.0-9.0 (optimum, pH 7.0) and in the presence of 0-3 % (w/v) NaCl (optimum, 0-1 %). Propionate and acetate were produced from glucose fermentation. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain TEYR-7T was a member of the phylum Actinobacteria, exhibiting the highest sequence similarity to Propioniciclava tarda DSM 22130T (94.3 %). The only respiratory quinone detected in strain TEYR-7T was menaquinone MK-9(H4) and the major cellular fatty acids (>10 %) were anteiso-C15 : 0 and C16 : 0. The polar lipid profile consisted of phosphatidylglycerol, diphosphatidylglycerol, two unidentified glycolipids, an unidentified phospholipid and three unidentified lipids. The genomic DNA G+C content was 71.2 mol%. meso-Diaminopimelic acid was detected in the peptidoglycan. On the basis of data from the present polyphasic taxonomic study, strain TEYR-7T is considered to represent a novel species of the genus Propioniciclava, for which the name Propioniciclava sinopodophylli sp. nov. is proposed. The type strain is TEYR-7T (=CCTCC AB 2015257T=KCTC 33808T).

SOS2-LIKE PROTEIN KINASE5, an SNF1-RELATED PROTEIN KINASE3-Type Protein Kinase, Is Important for Abscisic Acid Responses in Arabidopsis through Phosphorylation of ABSCISIC ACID-INSENSITIVE5.

Abscisic acid (ABA) plays an essential role in seed germination. In this study, we demonstrate that one SNF1-related protein kinase3-type protein kinase, SOS2-like protein kinase5 (PKS5), is involved in ABA signal transduction via the phosphorylation of an interacting protein, abscisic acid-insensitive5 (ABI5). We found that pks5-3 and pks5-4, two previously identified PKS5 superactive kinase mutants with point mutations in the PKS5 FISL/NAF (a conserved peptide that is necessary for interaction with SOS3 or SOS3-like calcium binding proteins) motif and the kinase domain, respectively, are hypersensitive to ABA during seed germination. PKS5 was found to interact with ABI5 in yeast (Saccharomyces cerevisiae), and this interaction was further confirmed in planta using bimolecular fluorescence complementation. Genetic studies revealed that ABI5 is epistatic to PKS5. PKS5 phosphorylates a serine (Ser) residue at position 42 in ABI5 and regulates ABA-responsive gene expression. This phosphorylation was induced by ABA in vivo and transactivated ABI5. Expression of ABI5, in which Ser-42 was mutated to alanine, could not fully rescue the ABA-insensitive phenotypes of the abi5-8 and pks5-4abi5-8 mutants. In contrast, mutating Ser-42 to aspartate rescued the ABA insensitivity of these mutants. These data demonstrate that PKS5-mediated phosphorylation of ABI5 at Ser-42 is critical for the ABA regulation of seed germination and gene expression in Arabidopsis (Arabidopsis thaliana).

BolOST1, an ortholog of Open Stomata 1 with alternative splicing products in Brassica oleracea, positively modulates drought responses in plants.

Open Stomata 1 (OST1), an ABA-activated sucrose non-fermenting 1 (SNF1)-related protein kinase, is critical for plant drought responses. We investigated the functions of two splicing isoforms of the OST1 ortholog in Brassica oleracea (BolOST1). BolOST1 expression was found to be dramatically induced by drought and high-salt stress, and the ectopic expression of BolOST1 restored the drought-sensitive phenotype of ost1. Subcellular localization revealed that BolOST1 is localized in both the nucleus and cytoplasm. BolOST1 was also demonstrated to phosphorylate the N-terminal fragment of ABI5 (ABA Insensitive 5, ABI5-N). A firefly luciferase complementation assay revealed that BolOST1 interacts with both BolABI5 and an ABI1 ortholog in B. oleracea (BolABI1). Overall, these results suggest that BolOST1 is a functional SnRK2-type protein kinase and that the early ABA signaling network may be conserved between Arabidopsis and cabbage.

Modulation Role of abscisic acid (ABA) on growth, water relations and glycinebetaine metabolism in two maize (Zea mays L.) cultivars under drought stress.

The role of plant hormone abscisic acid (ABA) in plants under drought stress (DS) is crucial in modulating physiological responses that eventually lead to adaptation to an unfavorable environment; however, the role of this hormone in modulation of glycinebetaine (GB) metabolism in maize particularly at the seedling stage is still poorly understood. Some hydroponic experiments were conducted to investigate the modulation role of ABA on plant growth, water relations and GB metabolism in the leaves of two maize cultivars, Zhengdan 958 (ZD958; drought tolerant), and Jundan 20 (JD20; drought sensitive), subjected to integrated root-zone drought stress (IR-DS) simulated by the addition of polyethylene glycol (PEG, 12% w/v, MW 6000). The IR-DS substantially resulted in increased betaine aldehyde dehydrogenase (BADH) activity and choline content which act as the key enzyme and initial substrate, respectively, in GB biosynthesis. Drought stress also induced accumulation of GB, whereas it caused reduction in leaf relative water content (RWC) and dry matter (DM) in both cultivars. The contents of ABA and GB increased in drought-stressed maize seedlings, but ABA accumulated prior to GB accumulation under the drought treatment. These responses were more predominant in ZD958 than those in JD20. Addition of exogenous ABA and fluridone (Flu) (ABA synthesis inhibitor) applied separately increased and decreased BADH activity, respectively. Abscisic acid application enhanced GB accumulation, leaf RWC and shoot DM production in both cultivars. However, of both maize cultivars, the drought sensitive maize cultivar (JD20) performed relatively better than the other maize cultivar ZD958 under both ABA and Flu application in view of all parameters appraised. It is, therefore, concluded that increase in both BADH activity and choline content possibly resulted in enhancement of GB accumulation under DS. The endogenous ABA was probably involved in the regulation of GB metabolism by regulating BADH activity, and resulting in modulation of water relations and plant growth under drought, especially in the drought sensitive maize cultivar JD20.

Genome-Wide Analysis of the bZIP Gene Family Identifies Two ABI5-Like bZIP Transcription Factors, BrABI5a and BrABI5b, as Positive Modulators of ABA Signalling in Chinese Cabbage.

bZIP (basic leucine zipper) transcription factors coordinate plant growth and development and control responses to environmental stimuli. The genome of Chinese cabbage (Brassica rapa) encodes 136 putative bZIP transcription factors. The bZIP transcription factors in Brassica rapa (BrbZIP) are classified into 10 subfamilies. Phylogenetic relationship analysis reveals that subfamily A consists of 23 BrbZIPs. Two BrbZIPs within subfamily A, Bra005287 and Bra017251, display high similarity to ABI5 (ABA Insensitive 5). Expression of subfamily A BrbZIPs, like BrABI5a (Bra005287/BrbZIP14) and BrABI5b (Bra017251/BrbZIP13), are significantly induced by the plant hormone ABA. Subcellular localization assay reveal that both BrABI5a and BrABI5b have a nuclear localization. BrABI5a and BrABI5b could directly stimulate ABA Responsive Element-driven HIS (a HIS3 reporter gene, which confers His prototrophy) or LUC (LUCIFERASE) expression in yeast and Arabidopsis protoplast. Deletion of the bZIP motif abolished BrABI5a and BrABI5b transcriptional activity. The ABA insensitive phenotype of Arabidopsis abi5-1 is completely suppressed in transgenic lines expressing BrABI5a or BrABI5b. Overall, these results suggest that ABI5 orthologs, BrABI5a and BrABI5b, have key roles in ABA signalling in Chinese cabbage.

Pyrabactin regulates root hydraulic properties in maize seedlings by affecting PIP aquaporins in a phosphorylation-dependent manner.

Pyrabactin, an agonist of abscisic acid (ABA), has led to the isolation and characterization of pyrabactin resistance 1/pyrabactin resistance 1-like (PYR1/PYLs) ABA receptors in Arabidopsis, which has well explained ABA-mediated stomatal movement and stress-related gene expression. In addition to inducing stomatal closure and inhibiting transpiration, ABA can also enhance root hydraulic conductivity (Lpr), thus maintaining water balance under water deficiency-related stress, but its molecular mechanism remains unclear. In the present study, the root hydraulic properties of maize seedlings in response to pyrabactin were compared to those caused by ABA. Similar to ABA, lower concentration of pyrabactin induced a remarkable increase in Lpr as well as in the gene expression of the plasma membrane intrinsic protein (ZmPIP) aquaporin and in the ZmPIP2; 1/2; 2 protein abundance. The pyrabactin-induced enhancement of Lpr was abolished by H2O2 application, indicating that pyrabactin regulates Lpr by modulating ZmPIP at transcriptional, translational and post-translational (activity) level. Pyrabactin-mediated water transport and ZmPIP gene expression were phosphorylation-dependent, suggesting that ABA-PYR1-(PP2C)-protein kinase-AQP signaling pathway may be involved in this process. As we know this is the first established ABA signaling transduction pathway that mediated water transport in roots. This observation further addressed the importance of PYR1/PYLs ABA receptor in regulating plant water use efficiency from the under ground level. Except inhibiting transpiration in leaves, our result introduces the exciting possibility of application ABA agonists for regulating roots water uptake in field, with a species- and dose dependent manner.