Xinhong Guo

Plastid casein kinase 2 knockout reduces abscisic acid (ABA) sensitivity, thermotolerance, and expression of ABA- and heat-stress-responsive nuclear genes

Summary This study demonstrated a role of plastid CK2 in ABA and heat-stress signalling. Its knockout led to reduced ABA sensitivity, thermotolerance, and expression of nuclear genes involved in these processes.

Abiotic stress upregulated TaZFP34 represses the expression of type-B response regulator and SHY2 genes and enhances root to shoot ratio in wheat

Q-type C2H2 zinc finger proteins (ZFPs) are plant-specific DNA-binding proteins containing a conserved QALGGH motif. This study investigated the function of abiotic stress-inducible and predominantly root-expressed Triticum aestivum ZFPs (TaZFP22, TaZFP34 and TaZFP46) with a focus on TaZFP34. Expression of TaZFP34 in roots was upregulated by high salinity, dehydration, oxidative and cold stresses. Overexpression of TaZFP34 in wheat roots resulted in an increased root-to-shoot ratio, a phenomenon observed during plant adaptation to drying soil. Expression of a number of genes which are potentially involved in modulating root growth was significantly altered in the roots of TaZFP34 overexpressing lines. In particular, the transcript levels of TaRR12B, TaRR12D and TaSHY2 that are homologues of known negative regulators of root growth were significantly reduced. Expression of shoot growth-related genes, such as GA3-ox and expansins, was downregulated in the transgenic shoots. TaZFP34 bound to (C/G)AGT(G/A)-like elements in the promoters of TaZFP34 down-regulated TaRR12D and TaSHY2 and transrepressed the reporter gene expression driven by TaRR12D and TaSHY2 promoters. Expression of the above reporter genes was also repressed by TaZFP46 and TaZFP22. These data suggest that TaZFP34 is a transcriptional repressor and is involved in modulating the root-to-shoot ratio.

CKB1 is involved in abscisic acid and gibberellic acid signaling to regulate stress responses in Arabidopsis thaliana

Casein kinase II (CK2), an evolutionarily well-conserved Ser/Thr kinase, plays critical roles in all higher organisms including plants. CKB1 is a regulatory subunit beta of CK2. In this study, homozygous T-DNA mutants (ckb1-1 and ckb1-2) and over-expression plants (35S:CKB1-1, 35S:CKB1-2) of Arabidopsis thaliana were studied to understand the role of CKB1 in abiotic stress and gibberellic acid (GA) signaling. Histochemical staining showed that although CKB1 was expressed in all organs, it had a relatively higher expression in conducting tissues. The ckb1 mutants showed reduced sensitivity to abscisic acid (ABA) during seed germination and seedling growth. The increased stomatal aperture, leaf water loss and proline accumulation were observed in ckb1 mutants. In contrast, the ckb1 mutant had increased sensitivity to polyaluminum chloride during seed germination and hypocotyl elongation. We obtained opposite results in over-expression plants. The expression levels of a number of genes in the ABA and GA regulatory network had changed. This study demonstrates that CKB1 is an ABA signaling-related gene, which subsequently influences GA metabolism, and may play a positive role in ABA signaling.

Arabidopsis casein kinase 1-like 2 involved in abscisic acid signal transduction pathways

In this study, we isolated a homozygous T-DNA insertion mutant line, ckl2, of the casein kinase 1-Like 2 (CKL2) gene in Arabidopsis thaliana. Through analysis of the germination ratio, root length, water loss rate, and stomatal aperture, we found that the ckl2 mutants showed an abscisic acid (ABA)-hyposensitive phenotype in all tests. CKL2 was also found to mediate the expression of ABA-upregulated genes in seeds and seedlings. CKL2 was expressed in all tissues, especially in the leaf and leaf stalk, and could be induced by ABA. A proline accumulation experiment showed that the Pro content in ckl2 was lower than that of the wild type. The above results demonstrate that CKL2 was required for ABA-regulated seed germination, root growth, and gene expression, suggesting that CKL2 positively mediates ABA signaling in Arabidopsis.

A glucuronokinase gene in Arabidopsis, AtGlcAK, is involved in drought tolerance by modulating sugar metabolism

Arabidopsis glucuronokinase (AtGlcAK), as a member of the GHMP kinases family, is implicated in the de novo synthesis of UDP-glucuronic acid (UDP-GlcA) by the myo-inositol oxygenation pathway. In this study, two T-DNA insertion homozygous mutants of AtGlcAK, atglcak-1 and atglcak-2, were identified. AtGlcAK was highly expressed in roots and flowers. There was reduced primary root elongation and lateral root formation in atglcak mutants under osmotic stress. The atglcak mutants displayed enhanced stomatal opening in response to abscisic acid (ABA), elevated water loss and impaired drought tolerance. Under water stress, the accumulation of reducing and soluble sugars was reduced in atglcak mutants, and the metabolism of glucose and sucrose was affected by the synthetic pathway of UDP-GlcA. Furthermore, a reduced level of starch in atglcak mutants was observed under normal conditions. The phylogenetic analysis suggested that GlcAK was conserved in numerous dicots and monocots plants. In short, AtGlcAK mutants displayed hypersensitivity to ABA and reduced root development under water stress, rendering the plants more susceptible to drought stress.

Genetic diversity revealed by morphological traits and ISSR markers in 48 Okras (Abelmoschus escullentus L.)

Okra is a widely distributed crop in the tropics, subtropics, and warmer areas of the temperate zones. Its major potential uses as a vegetable, oil and protein source, and source of paper pulp and fuel, or biomass are compatible. It is expected to have high value of exploitation and application. Due to the limited number of molecular studies focused on okras, the methods of morphological and ISSR markers were used to analysis the genetic diversity of 48 okras in the present study. The 22 primers were picked for ISSR-PCR, and a total of 154 fragments were amplified with an overall average polymorphism of 54.55xa0%. We used the 154 markers to construct the dendrogram based on the unweighted pair group method with arithmetic means (UPGMA). A high level of genetic diversity was found among 48 individuals. The 48 Okras was divided into four clusters at Dice’s coefficient of 0.19 with clustering analysis. Based on these data of the genetic diversity, it will be possible to exploit the available resources of okra in more valuable ways.

LecRK-VII.1, a Lectin Receptor-Like Kinase, Mediates the Regulation of Salt Stress and Jasmonic Acid Response in Arabidopsis

Lectin receptor-like kinases (LecRKs) are a class of membrane proteins found in higher plants. They play important roles in defense against of pathogens, perception of insect feeding, and stress tolerance. LecRK-VII.1 (AT4G04960) is one member of the LecRK family, which contains a conserved lectin domain and a kinase domain. In this study, the lecrk-VII.1 mutants (lecrk-VII.1-1 and lecrk-VII.1-2) showed increased seed germination rates and primary root length compared to ecotype Columbia-0 (Col-0) when treated with different concentrations of NaCl and methyl jasmonate (MeJA). To further confirm the possible role of LecRK-VII.1 in salt and jasmonic acid (JA) responses, we performed a comparative proteomic analysis of Arabidopsis Col-0 and lecrk-VII.1-1 mutant seedlings. In total, 312 proteins were differentially expressed of which 75 were related to stress responses including salt stress and JA response. Among them, decreased expressions of lipoxygenase (LOX) and annexin were confirmed by RT-PCR analyses. Activity of LOX was accordingly reduced in lecrk-VII.1 mutants. These results provide some valuable data to understand the role of LecRK-VII.1 in the response to salt stress and MeJA.Graphical AbstractIn order to understand the role of LecRK-VII.1 in the response to salt stress and MeJA, we studied the phenotypes and expression patterns between the lecrk-VII.1 mutants and wild type. Comparative proteomic analysis of differentially expressed proteins of the lecrk-VII.1 mutants and wild type in Arabidopsis was performed.

LecRKIII.1 and LecRKIII.2 formed homodimers to play physiological functions in Arabidopsis thaliana

Receptor-like kinases (RLKs), an important family that plant cell sense and transmit extracellular signals, are fundamental to plant cell life and play critical roles in various biological processes, such as response to abiotic stress, development and hormonal response. Among RLKs, the lectin receptor-like kinases (LecRLKs) possess a characteristic extracellular carbohydrate-binding lectin domain and play important roles in plant immune, stress and hormone responses. However, little is known about the genes LecRKIII.1 and LecRKIII.2 of LecRLK family up to now. Here, we founded that LecRKIII.1 and LecRKIII.2 were localized in plasma membrane and played the physiological roles by forming a homodimer. Real-time fluorescence quantitative PCR analysis of the expression level of LecRKIII.1 and LecRKIII.2 in response to exogenous ABA, MeJA, SA, NaCl, mannitol and dehydration suggested that LecRKIII.1 and LecRKIII.2 may play important roles in response to various stresses. It will lay a good foundation for further studies on physiological functions of LecRKIII.1 and LecRKIII.2.

Quantitative phosphoproteomics of lectin receptor-like kinase VI.4 dependent abscisic acid response in Arabidopsis thaliana

Lectin receptor-like kinases (LecRKs) play important roles in the responses to adverse environment stress. Abscisic acid (ABA) is a plant hormone involved in plant growth, development and adverse environmental stress responses. Although some studies of ABA response LecRK genes have been reported, the molecular mechanisms of LecRKs regulation of downstream pathways under ABA induction are not well understood. The present study showed that LecRK-VI.4 responded to ABA and negatively regulated stomatal closure. Here, a quantitative phosphoproteomics approach based on mass spectrometry was employed to study the roles of LecRK-VI.4 in the ABA signaling pathway. Metal oxide affinity beads and C18 chromatography were used for phosphopeptide enrichment and separation. The isobaric tags for relative and absolute quantitation were used for profiling the phosphoproteome of mutant lecrk-vi.4-1 and wild-type Col-0 Arabidopsis under normal growth conditions or ABA treatments. In total, 475 unique phosphopeptides were quantified, including 81 phosphopeptides related to LecRK-VI.4 regulation. Gene ontology, protein-protein interaction and motif analysis were performed. The bioinformatics data showed that phosphorylated proteins regulated by LecRK-VI.4 had close relations with factors of stomatal function, which included aquaporin activity, H+ pump activity and the Ca2+ concentration in the cytoplasm. These data have expanded our understanding of how LecRK-VI.4 regulates ABA-mediated stomatal movements.

Genome-wide identification, classification and expression analysis of GHMP genes family in Arabidopsis thaliana

The GHMP genes family, a unique class of ATP-dependent enzymes, consists of galactokinases, homoserine kinases, mevalonate kinases and phosphomevalonate kinase etc. It was implicated in the biosynthesis of isoprenes and amino acids as well as in carbohydrate metabolism. Previous studies mainly focused on the structure, catalytic mechanism or function in abiotic stress signaling. In this study, we integrated the research progress on GHMP genes and identified 12 members (five previously discovered and seven newly identified here) of this family in Arabidopsis thaliana. The gene ontology, phylogenetic relationship, motifs, cis-acting element, expression profiles, structures and protein–protein interaction network of GHMP family were analyzed. The neighbor-joining tree and cluster of gene structures indicated that the 12 members were divided into two classes. The three motifs in the GHMP family were highly conserved among the GHMP family by Multiple EM for Motif Elicitation, providing further proof on their phylogenetic relationship. Additionally, prediction on cis-acting elements indicated that these genes were likely to be involved in multiple responses stimulated by various hormones and abiotic stress. It is roughly consistent with the data of microarray. The identification and bioinformatic analysis of GHMP family in Arabidopsis thaliana could provide reference data for further study on their biological functions, especially in the responsiveness to hormones and stress signaling.