GsSRK, a G-type lectin S-receptor-like serine/threonine protein kinase,is a positive regulator of plant tolerance to salt stress

Receptor-like protein kinases (RLKs) play vital roles in sensing outside signals, yet little is known about RLKs functions and roles in stress signal perception and transduction in plants, especially in wild soybean. Through the microarray analysis, GsSRK was identified as an alkaline (NaHCO₃)-responsive gene, and was subsequently isolated from Glycine soja by homologous cloning. GsSRK encodes a 93.22 kDa protein with a highly conserved serine/threonine protein kinase catalytic domain, a G-type lectin region, and an S-locus region. Real-time PCR results showed that the expression levels of GsSRK were largely induced by ABA, salt, and drought stresses. Over expression of GsSRK in Arabidopsis promoted seed germination, as well as primary root and rosette leaf growth during the early stages of salt stress. Compared to the wild type Arabidopsis, GsSRK overexpressors exhibited enhanced salt tolerance and higher yields under salt stress, with higher chlorophyll content, lower ion leakage, higher plant height, and more siliques at the adult developmental stage. Our studies suggest that GsSRK plays a crucial role in plant response to salt stress.     

一个具有S位点的水稻类受体激酶OsSRL参与干旱胁迫反应

植物在进化过程中针对干旱、高盐和高低温等逆境胁迫形成了多种适应机制, 植物类受体激酶作为重要的细胞信号传递分子在植物生长和抗逆境胁迫中发挥着重要功能。该文发现一个具有S位点的类受体激酶基因OsSRL可能参与水稻(Oryza sativa)的干旱胁迫反应。利用RNAi技术降低OsSRL的表达水平后, 转基因植株抗旱性增强, 并表现出幼苗存活率、叶绿素含量及鲜重增加等表型。进一步的研究表明30%PEG和100 μmol·L^–1ABA可诱导OsSRL基因表达, 利用RNAi降低其表达导致干旱诱导基因RAB16A及LEA3表达水平明显增加。表达模式分析发现OsSRL在胚芽、胚根、根、茎节以及花中表达。以上结果表明, OsSRL表达水平的降低增强植物的干旱耐受性, 其作为一个S-位点样类受体激酶可能参与了水稻对干旱胁迫的反应。     

Identification of a receptor-like protein kinase gene rapidly induced by abscisic acid, dehydration, high salt, and cold treatments in Arabidopsis thaliana.

A cDNA clone for a receptor-like protein kinase gene (RPK1) was isolated from Arabidopsis thaliana. The clone is 1952 bp long with 1623 bp of an open reading frame encoding a peptide of 540 amino acids. The deduced peptide (RPK1) contains four distinctive domains characteristic of receptor kinases: (a) a putative amino-terminal signal sequence domain; (b) a domain with five extracellular leucine-rich repeat sequences; (c) a membrane-spanning domain; and (d) a cytoplasmic protein kinase domain that contains all of the 11 subdomains conserved among protein kinases. The RPK1 gene is expressed in flowers, stems, leaves, and roots. Expression of the RPK1 gene is induced within 1 h after treatment with abscisic acid (ABA). The gene is also rapidly induced by several environmental stresses such as dehydration, high salt, and low temperature, suggesting that the gene is involved in a general stress response. The dehydration-induced expression is not impaired in aba-1, abi1-1, abi2-1, and abi3-1 mutants, suggesting that the dehydration-induced expression of the RPK1 gene is ABA-independent. A possible role of this gene in the signal transduction pathway of ABA and the environmental stresses is discussed.     

Calcium/calmodulin up-regulates a cytoplasmic receptor-like kinase in plants

Calcium/calmodulin-dependent kinases play an important role in protein phosphorylation in eukaryotes. However, not much is known about calcium/calmodulin-dependent protein phosphorylation and its role in signal transduction in plants. By using a protein-protein interaction-based approach, we have isolated a novel plant-specific calmodulin-binding receptor-like cytoplasmic kinase (CRCK1) from Arabidopsis thaliana, as well as its ortholog from Medicago sativa (alfalfa). CRCK1 does not show high homology to calcium/calmodulin-dependent protein kinases in animals. In contrast, it shows high homology in the kinase domain to serine/threonine receptor-like kinases in plants. However, it contains neither a transmembrane domain nor an extracellular domain. Calmodulin binds to CRCK1 in a calcium-dependent manner with an affinity of approximately 20.5 nm. The calmodulin-binding site in CRCK1 is located in amino acids 160-183, which overlap subdomain II of the kinase domain. CRCK1 undergoes autophosphorylation in the presence of Mg2+ at the threonine residue(s). The Km and Vmax values of CRCK1 for ATP are 1 microm and 33.6 pmol/mg/min, respectively. Calcium/calmodulin stimulates the kinase activity of CRCK1, which increases the Vmax of CRCK1 approximately 9-fold. The expression of CRCK1 is increased in response to stresses such as cold and salt and stress molecules such as abscisic acid and hydrogen peroxide. These results indicate the presence of a calcium/calmodulin-regulated receptor-like cytoplasmic kinase in plants. Furthermore, these results also suggest that calcium/calmodulin-regulated protein phosphorylation involving CRCK1 plays a role in stress signal transduction in plants.     

Effect of shade on leaf photosynthetic capacity,light-intercepting,electron transfer and energy distribution of soybeans

Lectin receptor-like kinases (LecRLK) are widespread in higher plants and their effects on abiotic stress tolerance are gradually being reported. However, little information is available on LecRLK functions in bryophytes. Here, an L-type LecRLK gene (PnLecRLK1) was characterized from the Antarctic moss Pohlia nutans. Subcellular localization analysis revealed that PnLecRLK1 was a plasma membrane protein. The expression of PnLecRLK1 was rapidly induced by simulated cold, salt, and drought stresses as well as by exogenously applied abscisic acid (ABA) and methyl jasmonate. Transgenic Arabidopsis plants of overexpressing PnLecRLK1 exhibited enhanced tolerance to chilling-stress and increased ABA sensitivity. Additionally, the expression levels of genes in the C-repeat binding factor (CBF) signaling pathway such as AtCBF1, AtCBF2, AtCBF3 and AtCOR47 were markedly increased in transgenic Arabidopsis. Furthermore, the expression levels of ABA-responsive genes, such as AtABI4, AtABI5, AtMYB2 and AtDREB2A, were also significantly up-regulated in transgenic Arabidopsis. Therefore, our results suggested that PnLecRLK1 functions as a membrane-bound regulator that increases chilling stress tolerance and ABA sensitivity to enable P. nutans to adapt to polar climates.     

A Role for Arabidopsis miR399f in Salt,Drought, and ABA Signaling

MiR399f plays a crucial role in maintaining phosphate homeostasis in Arabidopsis thaliana. Under phosphate starvation conditions, AtMYB2, which plays a role in plant salt and drought stress responses, directly regulates the expression of miR399f. In this study, we found that miR399f also participates in plant responses to abscisic acid (ABA), and to abiotic stresses including salt and drought. Salt and ABA treatment induced the expression of miR399f, as confirmed by histochemical analysis of promoter-GUS fusions. Transgenic Arabidopsis plants overexpressing miR399f (miR399f-OE) exhibited enhanced tolerance to salt stress and exogenous ABA, but hypersensitivity to drought. Our in silico analysis identified ABF3 and CSP41b as putative target genes of miR399f, and expression analysis revealed that mRNA levels of ABF3 and CSP41b decreased remarkably in miR399f-OE plants under salt stress and in response to treatment with ABA. Moreover, we showed that activation of stress-responsive gene expression in response to salt stress and ABA treatment was impaired in miR399f-OE plants. Thus, these results suggested that in addition to phosphate starvation signaling, miR399f might also modulates plant responses to salt, ABA, and drought, by regulating the expression of newly discovered target genes such as ABF3 and CSP41b.     

A Novel ABA-Responsive TaSRHP Gene from Wheat Contributes to Enhanced Resistance to Salt Stress in Arabidopsis thaliana

A microarray analysis of the salt-resistant wheat mutant, RH8706-49, revealed a salt-induced gene containing a conserved DUF581 domain. The gene was cloned and designated as Triticum aestivum salt-related hypothetical protein (TaSRHP) and submitted to GenBank (accession no. GQ476575). Over-expression of TaSRHP in wild-type Arabidopsis thaliana cv. Columbia resulted in enhanced resistance to both salt and drought stresses. The sensitivity of the transgenic A. thaliana to abscisic acid (ABA) was also increased compared to that of wild-type plants. Furthermore, transgenic plants accumulated more K⁺ and proline and had a higher osmotic potential and lower Na⁺ content than untransformed plants. Real-time quantitative PCR analysis indicated that expression of TaSRHP was affected by salt, drought, cold, ABA, and other stresses, and expression of other stress-related genes in the transgenic plants differed from those of the control. Results indicate that the wheat TaSRHP gene may enhance the tolerance of plants to multiple abiotic stresses.     

Overproduction of the Membrane-bound Receptor-like Protein Kinase 1, RPK1, Enhances Abiotic Stress Tolerance in Arabidopsis

RPK1 (receptor-like protein kinase 1) localizes to the plasma membrane and functions as a regulator of abscisic acid (ABA) signaling in Arabidopsis. In our current study, we investigated the effect of RPK1 disruption and overproduction upon plant responses to drought stress. Transgenic Arabidopsis overexpressing the RPK1 protein showed increased ABA sensitivity in their root growth and stomatal closure and also displayed less transpirational water loss. In contrast, a mutant lacking RPK1 function, rpk1-1, was found to be resistant to ABA during these processes and showed increased water loss. RPK1 overproduction in these transgenic plants thus increased their tolerance to drought stress. We performed microarray analysis of RPK1 transgenic plants and observed enhanced expression of several stress-responsive genes, such as Cor15a, Cor15b, and rd29A, in addition to H₂O₂-responsive genes. Consistently, the expression levels of ABA/stress-responsive genes in rpk1-1 had decreased compared with wild type. The results suggest that the overproduction of RPK1 enhances both the ABA and drought stress signaling pathways. Furthermore, the leaves of the rpk1-1 plants exhibit higher sensitivity to oxidative stress upon ABA-pretreatment, whereas transgenic plants overproducing RPK1 manifest increased tolerance to this stress. Our current data suggest therefore that RPK1 overproduction controls reactive oxygen species homeostasis and enhances both water and oxidative stress tolerance in Arabidopsis.     

OsCIPK31, a CBL-interacting protein kinase is involved in germination and seedling growth under abiotic stress conditions in rice plants

Calcineurin B-like protein-interacting protein kinases (CIPKs) are a group of typical Ser/Thr protein kinases that mediate calcium signals. Extensive studies using Arabidopsis plants have demonstrated that many calcium signatures that activate CIPKs originate from abiotic stresses. However, there are few reports on the functional demonstration of CIPKs in other plants, especially in grasses. In this study, we used a loss-of-function mutation to characterize the function of the rice CIPK gene OsCIPK31. Exposure to high concentrations of NaCl or mannitol effected a rapid and transient enhancement of OsCIPK31 expression. These findings were observed only in the light. However, longer exposure to most stresses resulted in downregulation of OsCIPK31 expression in both the presence and absence of light. To determine the physiological roles of OsCIPK31 in rice plants, the sensitivity of oscipk31::Ds, which is a transposon Ds insertion mutant, to abiotic stresses was examined during germination and seedling stages. oscipk31::Ds mutants exhibited hypersensitive phenotypes to ABA, salt, mannitol, and glucose. Compared with wild-type rice plants, mutants exhibited retarded germination and slow seedling growth. In addition, oscipk31::Ds seedlings exhibited enhanced expression of several stress-responsive genes after exposure to these abiotic stresses. However, the expression of ABA metabolic genes and the endogenous levels of ABA were not altered significantly in the oscipk31::Ds mutant. This study demonstrated that rice plants use OsCIPK31 to modulate responses to abiotic stresses during the seed germination and seedling stages and to modulate the expression of stress-responsive genes.     

SbRLK1, a receptor-like protein kinase of Sorghum bicolor (L.) Moench that is expressed in mesophyll cells

To study the metabolic interactions between mesophyll and bundle-sheath cells of C₄ plants, protein kinases possibly involved in the regulatory processes and signal transduction pathways have been cloned and characterized. A receptor-like protein kinase (RLK) cDNA clone from the C₄ plant Sorghum bicolor (L.) Moench has been identified. The deduced protein was designated SbRLK1 for receptor-like protein kinase from S. bicolor. The putative cytoplasmic domain of SbRLK1 contains all amino acids that are characteristic of protein kinases. The extracellular domain contains five leucine-rich repeats. The mRNA of the SbRLK1 gene accumulated to much higher levels in mesophyll cells than in the bundle-sheath and was almost undetectable in roots. This expression pattern indicates that SbRLK1 might be involved in the regulation of specific processes in mesophyll cells. Received: 13 August 1998 / Accepted: 22 December 1998     

JcLEA,a Novel LEA-Like Protein from Jatropha curcas,Confers a High Level of Tolerance to Dehydration and Salinity in Arabidopsis thaliana

Jatropha curcas L. is a highly drought and salt tolerant plant species that is typically used as a traditional folk medicine and biofuel crop in many countries. Understanding the molecular mechanisms that underlie the response to various abiotic environmental stimuli, especially to drought and salt stresses, in J. curcas could be important to crop improvement efforts. In this study, we cloned and characterized the gene for a late embryogenesis abundant (LEA) protein from J. curcas that we designated JcLEA. Sequence analyses showed that the JcLEA protein belongs to group 5, a subgroup of the LEA protein family. In young seedlings, expression of JcLEA is significantly induced by abscisic acid (ABA), dehydration, and salt stress. Subcellular localization analysis shows that that JcLEA protein is distributed in both the nucleus and cytoplasm. Moreover, based on growth status and physiological indices, the overexpression of JcLEA in transgenic Arabidopsis plants conferred increased resistance to both drought and salt stresses compared to the WT. Our data suggests that the group 5 JcLEA protein contributes to drought and salt stress tolerance in plants. Thus, JcLEA is a potential candidate gene for plant genetic modification.     

A Leucine-Rich Repeat Receptor-like Kinase from the Antarctic Moss <Emphasis Type="Italic">Pohlia nutans</Emphasis> Confers Salinity and ABA Stress Tolerance

Plant leucine-rich repeats receptor-like kinases (LRR-RLKs) play key roles in plant growth, development, and responses to environmental stresses. However, the functions of LRR-RLKs in bryophytes are still not well documented. Here, a putative LRR-RLK gene, PnLRR-RLK, was cloned and characterized from the Antarctic moss Pohlia nutans. Phylogenetic analysis revealed that PnLRR-RLK protein was clustered with the Arabidopsis thaliana LRR XI family proteins. Subcellular localization analysis of PnLRR-RLK revealed that it was mainly localized on plasma membrane. The expression of PnLRR-RLK was induced by mock high salinity, cold, drought, and exogenously supplied abscisic acid (ABA) and methyl jasmonate (MeJA). Meanwhile, the overexpression of PnLRR-RLK showed an increased tolerance of transgenic Arabidopsis to salt and ABA stresses than that of the wild type (WT) plants. Furthermore, the expression levels of several salt tolerance genes (AtHKT1, AtSOS3, AtP5CS1, and AtADH1) and an ABA negatively regulating gene AtABI1 were significantly increased in transgenic plants. Meanwhile, the expression levels of ABA biosynthesis genes (AtNCED3, AtABA1, and AtAAO3) and ABA early response genes (AtMYB2, AtRD22, AtRD29A, and AtDREB2A) were decreased in transgenic Arabidopsis after salt stress treatment. Therefore, these results suggested that PnLRR-RLK might involve in regulating salt stress-related and ABA-dependent signaling pathway, thereby contribute to the salinity tolerance of the Antarctic moss P. nutans.