scholarly journals Interruption of Jasmonic Acid Biosynthesis Causes Differential Responses in the Roots and Shoots of Maize Seedlings against Salt Stress

2019 ◽  
Vol 20 (24) ◽  
pp. 6202 ◽  
Author(s):  
Ramala Masood Ahmad ◽  
Cheng Cheng ◽  
Jia Sheng ◽  
Wei Wang ◽  
Hong Ren ◽  
...  

Jasmonates (JAs) together with jasmonic acid and its offshoots are lipid-derived endogenous hormones that play key roles in both developmental processes and different defense responses in plants. JAs have been studied intensively in the past decades for their substantial roles in plant defense comebacks against diverse environmental stresses among model plants. However, the role of this phytohormone has been poorly investigated in the monocotyledonous species against abiotic stresses. In this study, a JA biosynthesis mutant opr7opr8 was used for the investigation of JA roles in the salt stress responses of maize seedlings, whose roots were exposed to 0 to 300 mM NaCl. Foliar stomatal observation showed that opr7opr8 had a larger stomatal aperture than wild type (WT) (B73) under salinity stress, indicating that JA positively regulates guard cell movement under salt stress. The results regarding chlorophyll content and leaf senescence showed that opr7opr8 exhibited delayed leaf senescence under salt stress as compared to WT, indicating that JA plays a role in salt-inducing cell death and subsequent leaf senescence. Moreover, the morphological parameters, including the length of the shoots and roots, and the fresh and dry weights of the shoots and roots, showed that after 7 days of salt treatment, opr7opr8 had heavier and longer shoots than WT but slighter and shorter roots than WT. In addition, ion analysis showed that opr7opr8 accumulated less sodium but more potassium in the leaves than WT but more sodium and less potassium in the roots than WT, suggesting that JA deficiency causes higher salt stress to the roots but less stress to the leaves of the seedlings. Reactive oxygen species (ROS) analysis showed that opr7opr8 produced less H2O2 than WT in the leaves but more H2O2 in the roots under salt treatment, and correspondingly, ROS-scavenging enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) showed a similar variation, i.e., opr7opr8 has lower enzymatic activities in the shoots but higher activities in the roots than WT under salt treatment. For osmotic adjustment, opr7opr8 produced less proline in the shoots at 100 and 300 mM NaCl treatments but more in the roots than the WT roots under all salt treatments. In addition, the gene expression for abscisic acid (ABA) biosynthesis under salt stress was investigated. Results showed that the expression levels of four key enzymes of ABA biosynthesis, ZEP1, NCED5, AO1, and VP10, were significantly downregulated in the shoots as compared to WT under salt treatment. Putting all the data together, we concluded that JA-deficiency in maize seedlings reduced the salt-stress responses in the shoots but exaggerated the responses in the roots. In addition, endogenous JA acted as a positive regulator for the transportation of sodium ions from the roots to the shoots because the mutant opr7opr8 had a higher level of sodium in the roots but a significantly lower level in the shoots than WT. Furthermore, JA may act as a positive regulator for ABA biosynthesis in the leaves under salt stress.

2021 ◽  
Vol 12 ◽  
Author(s):  
Susana Serrazina ◽  
Helena Machado ◽  
Rita Lourenço Costa ◽  
Paula Duque ◽  
Rui Malhó

Allene oxide synthase (AOS) is a key enzyme of the jasmonic acid (JA) signaling pathway. The AOS gene was previously found to be upregulated in an Asian chestnut species resistant to infection by the oomycete Phytophthora cinnamomi (Castanea crenata), while lower expression values were detected in the susceptible European chestnut (Castanea sativa). Here, we report a genetic and functional characterization of the C. crenata AOS (CcAOS) upon its heterologous gene expression in a susceptible ecotype of Arabidopsis thaliana, which contains a single AOS gene. It was found that Arabidopsis plants expressing CcAOS delay pathogen progression and exhibit more vigorous growth in its presence. They also show upregulation of jasmonic acid and salicylic acid-related genes. As in its native species, heterologous CcAOS localized to plastids, as revealed by confocal imaging of the CcAOS-eGFP fusion protein in transgenic Arabidopsis roots. This observation was confirmed upon transient expression in Nicotiana benthamiana leaf epidermal cells. To further confirm a specific role of CcAOS in the defense mechanism against the pathogen, we performed crosses between transgenic CcAOS plants and an infertile Arabidopsis AOS knockout mutant line. It was found that plants expressing CcAOS exhibit normal growth, remain infertile but are significantly more tolerant to the pathogen than wild type plants. Together, our results indicate that CcAOS is an important player in plant defense responses against oomycete infection and that its expression in susceptible varieties may be a valuable tool to mitigate biotic stress responses.


Author(s):  
Taehoon Kim ◽  
Kiyoon Kang ◽  
Suk-Hwan Kim ◽  
Gynheung An ◽  
Nam-Chon Paek

The onset of leaf senescence is triggered by external cues and internal factors such as phytohormones and signaling pathways involving transcription factors (TFs). Abscisic acid (ABA) strongly induces senescence and endogenous ABA levels are finely tuned by many senescence-associated TFs. Here, we report on the regulatory function of the senescence-induced TF OsWRKY5 TF in rice (Oryza sativa). OsWRKY5 expression was rapidly upregulated in senescing leaves, especially in yellowing sectors initiated by aging or dark treatment. A T-DNA insertion activation-tagged OsWRKY5-overexpressing mutant (termed oswrky5-D) promoted leaf senescence under natural and dark-induced senescence (DIS) conditions. By contrast, a T-DNA insertion oswrky5-knockdown mutant (termed oswrky5) retained leaf greenness during DIS. Reverse-transcription quantitative PCR (RT-qPCR) showed that OsWRKY5 upregulates the expression of genes controlling chlorophyll degradation and leaf senescence. Furthermore, RT-qPCR and yeast one-hybrid analysis demonstrated that OsWRKY5 indirectly upregulates the expression of senescence-associated NAC genes including OsNAP and OsNAC2. Precocious leaf yellowing in the oswrky5-D mutant might be caused by elevated endogenous ABA concentrations resulting from upregulated expression of ABA biosynthesis genes OsNCED3, OsNCED4, and OsNCED5, indicating that OsWRKY is a positive regulator of ABA biosynthesis during leaf senescence. Furthermore, OsWRKY5 expression was significantly suppressed by ABA treatment, indicating negative feedback regulation of OsWRKY5 expression by ABA. OsWRKY5 is a positive regulator of leaf senescence that upregulates senescence-induced NAC genes leading to expression of ABA biosynthesis and chlorophyll degradation genes.


Rice ◽  
2021 ◽  
Vol 14 (1) ◽  
Author(s):  
R. A. O. Yuchun ◽  
J. I. A. O. Ran ◽  
W. A. N. G. Sheng ◽  
W. U. Xianmei ◽  
Y. E. Hanfei ◽  
...  

AbstractLesion mimic mutants spontaneously produce disease spots in the absence of biotic or abiotic stresses. Analyzing lesion mimic mutants’ sheds light on the mechanisms underlying programmed cell death and defense-related responses in plants. Here, we isolated and characterized the rice (Oryza sativa) spotted leaf 36 (spl36) mutant, which was identified from an ethyl methanesulfonate-mutagenized japonica cultivar Yundao population. spl36 displayed spontaneous cell death and enhanced resistance to rice bacterial pathogens. Gene expression analysis suggested that spl36 functions in the disease response by upregulating the expression of defense-related genes. Physiological and biochemical experiments indicated that more cell death occurred in spl36 than the wild type and that plant growth and development were affected in this mutant. We isolated SPL36 by map-based cloning. A single base substitution was detected in spl36, which results in a cysteine-to-arginine substitution in SPL36. SPL36 is predicted to encode a receptor-like protein kinase containing leucine-rich domains that may be involved in stress responses in rice. spl36 was more sensitive to salt stress than the wild type, suggesting that SPL36 also negatively regulates the salt-stress response. These findings suggest that SPL36 regulates the disease resistance response in rice by affecting the expression of defense- and stress-related genes.


Rice ◽  
2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Fan Zhang ◽  
Dan Zeng ◽  
Liyu Huang ◽  
Yingyao Shi ◽  
Tengjun Chen ◽  
...  

Abstract Background Salt stress and bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) are key limiting factors of rice (Oryza sativa L.) yields. Members of sucrose non-fermenting 1 (SNF1)-related protein kinase 2 (SnRK2), which is a family of plant-specific Ser/Thr kinases, are important components of signaling pathways involved in plant developmental processes and responses to stresses. There are 10 members of the SnRK2 family in rice; however, their functions are poorly understood, as are the underlying molecular mechanisms. Results In this study, we found that OsSAPK9, which belongs to the SnRK2 family, positively regulated salt-stress tolerance and strain-specific resistance to bacterial blight in rice. RNA sequencing revealed that there were 404 and 1324 genes differentially expressed in OsSAPK9-RNAi in comparison with wild-type plants under salt-stress conditions and after Xoo inoculation, respectively, which participate in basic metabolic processes. In total, 65 common differentially expressed genes involved mainly in defense responses were detected both under salt-stress conditions and after Xoo inoculation. Moreover, in vivo and in vitro experiments demonstrated that OsSAPK9 forms a protein complex with the molecular chaperones OsSGT1 and OsHsp90, and transgenic plants overexpressing OsSGT1 exhibited decreased tolerances to salt stress and significantly increased resistance levels to bacterial blight. Thus, OsSAPK9 may function as a center node regulator of salt-stress responses and disease-resistance pathways through its interaction with OsSGT1 in rice. Conclusion This study confirms that OsSAPK9 functions as a positive regulator of salt-stress responses and disease resistance through its interaction with OsSGT1 in rice.


2020 ◽  
Author(s):  
Susana Serrazina ◽  
Helena Machado ◽  
Rita Costa ◽  
Paula Duque ◽  
Rui Malhó

ABSTRACTAllene oxide synthase (AOS) is a key enzyme of the jasmonic acid (JA) signaling pathway. The AOS gene was previously found to be upregulated in an Asian chestnut species resistant to infection by the oomycete Phytophthora cinnamomi (Castanea crenata), while lower expression values were detected in the susceptible European chestnut (Castanea sativa). Here, we report a genetic and functional characterization of the C. crenata AOS (CcAOS) upon its heterologous gene expression in a susceptible ecotype of Arabidopsis thaliana, which contains a single AOS gene. It was found that Arabidopsis plants expressing CcAOS delay pathogen progression and exhibit more vigorous growth in its presence. They also show upregulation of jasmonic acid and salicylic acid-related genes. As in its native species, heterologous CcAOS localized to plastids, as revealed by confocal imaging of the CcAOS-eGFP fusion protein in transgenic Arabidopsis roots. This observation was confirmed upon transient expression in Nicotiana benthamiana leaf epidermal cells. To further confirm a specific role of CcAOS in the defense mechanism against the pathogen, we performed crosses between transgenic CcAOS plants and an infertile Arabidopsis AOS knockout mutant line. It was found that plants expressing CcAOS exhibit normal growth, remain infertile but are significantly more tolerant to the pathogen than wild type plants.Together, our results indicate that CcAOS is an important player in plant defense responses against oomycete infection and that its expression in susceptible varieties may be a valuable tool to mitigate biotic stress responses.One-sentence summaryHeterologous expression of the Castanea crenata allene oxide synthase gene in Arabidopsis thaliana improves the defense response to the pathogen Phytophthora cinnamomi.


2019 ◽  
Vol 20 (18) ◽  
pp. 4437 ◽  
Author(s):  
Kim ◽  
Kang ◽  
Kim ◽  
An ◽  
Paek

he onset of leaf senescence is triggered by external cues and internal factors such as phytohormones and signaling pathways involving transcription factors (TFs). Abscisic acid (ABA) strongly induces senescence and endogenous ABA levels are finely tuned by many senescence-associated TFs. Here, we report on the regulatory function of the senescence-induced TF OsWRKY5 TF in rice (Oryza sativa). OsWRKY5 expression was rapidly upregulated in senescing leaves, especially in yellowing sectors initiated by aging or dark treatment. A T-DNA insertion activation-tagged OsWRKY5-overexpressing mutant (termed oswrky5-D) promoted leaf senescence under natural and dark-induced senescence (DIS) conditions. By contrast, a T-DNA insertion oswrky5-knockdown mutant (termed oswrky5) retained leaf greenness during DIS. Reverse-transcription quantitative PCR (RT-qPCR) showed that OsWRKY5 upregulates the expression of genes controlling chlorophyll degradation and leaf senescence. Furthermore, RT-qPCR and yeast one-hybrid analysis demonstrated that OsWRKY5 indirectly upregulates the expression of senescence-associated NAM/ATAF1/2/CUC2 (NAC) genes including OsNAP and OsNAC2. Precocious leaf yellowing in the oswrky5-D mutant might be caused by elevated endogenous ABA concentrations resulting from upregulated expression of ABA biosynthesis genes OsNCED3, OsNCED4, and OsNCED5, indicating that OsWRKY is a positive regulator of ABA biosynthesis during leaf senescence. Furthermore, OsWRKY5 expression was suppressed by ABA treatment. Taken together, OsWRKY5 is a positive regulator of leaf senescence that upregulates senescence-induced NAC, ABA biosynthesis, and chlorophyll degradation genes.


2020 ◽  
Author(s):  
Xiamusiya Kakan ◽  
Yanwen Yu ◽  
Shenghui Li ◽  
Xiaoying Li ◽  
Rongfeng Huang ◽  
...  

Abstract Background:Abscisic acid (ABA) plays an important role in plant abiotic stress responses, and ABA INSENSITIVE 4 (ABI4) is a pivotal transcription factor in the ABA signaling pathway. In Arabidopsis, ABI4 negatively regulates salt tolerance; however, the mechanism through which ABI4 regulates plant salt tolerance is poorly understood. Our previous study showed that ABI4 directly binds to the promoter of the VITAMIN C DEFECTIVE 2 (VTC2) gene, inhibiting the transcription of VTC2 and ascorbic acid (AsA) biosynthesis.Results: In the present study, we found that treatment with exogenous AsA could alleviate salt stress sensitivity of ABI4-overexpressing transgenic plants. The decreased AsA content and increased reactive oxygen species (ROS) levels in ABI4-overexpressing seedlings under salt treatment indicated that AsA-promoted ROS scavenging was related to ABI4-mediated salt tolerance. Gene expression analysis showed that ABI4 was induced at the early stage of salt stress, giving rise to reduced VTC2 expression. Accordingly, the abundance of the VTC2 protein decreased under the same salt stress conditions, and was absent in the ABI4 loss-of-function mutants, suggesting that the transcriptional inhibition of ABI4 on VTC2 resulted in the attenuation of VTC2 function. In addition, other encoding genes in the AsA biosynthesis and recycling pathways showed different responses to salt stress, demonstrating that AsA homeostasis is complicated under salinity stress. Conclusions: This study elucidates the negative modulation of ABI4 in salt stress tolerance through the regulation of AsA biosynthesis and ROS accumulation in plants.


2021 ◽  
Vol 12 ◽  
Author(s):  
Zheng Chen ◽  
Wei Jia ◽  
Songwei Li ◽  
Jiayang Xu ◽  
Zicheng Xu

Melatonin (MEL) is a pleiotropic agent with crucial functions reported in a variety of stress responses and developmental processes. Although MEL involvement in plant defense against natural leaf senescence has been widely reported, the precise regulatory mechanisms by which it delays stress-induced senescence remain unclear. In this study, we found that foliar spraying of melatonin markedly ameliorated dehydration-induced leaf senescence in Nicotiana tabacum, accompanied by attenuated oxidative damage, expression of senescence-related genes, and reduced endogenous ABA production. Metabolite profiling indicated that melatonin-treated plants accumulated higher concentrations of sugars, sugar alcohol, and organic acids, but fewer concentrations of amino acids in the leaves, than untreated plants after exposure to dehydration. Gene expression analysis revealed that the delayed senescence of stressed plants achieved by melatonin treatment might be partially ascribed to the upregulated expression of genes involved in ROS scavenging, chlorophyll biosynthesis, photosynthesis, and carbon/nitrogen balances, and downregulated expression of senescence-associated genes. Furthermore, hormone responses showed an extensively modulated expression, complemented by carotenoid biosynthesis regulation to achieve growth acceleration in melatonin-treated plants upon exposure to dehydration stress. These findings may provide more comprehensive insights into the role of melatonin in alleviating leaf senescence and enhancing dehydration resistance.


2016 ◽  
Vol 43 (3) ◽  
pp. 232
Author(s):  
Vineeta Rai ◽  
Shayan Sarkar ◽  
Suresh Satpati ◽  
Nrisingha Dey

Peroxisomal enoyl-CoA delta isomerase2 (PECI2) is one of the key enzymes that has critical role in lipid metabolism and plant development during salt stress. Seven out of ten tobacco plants overexpressing human PECI2 (HsPECI2) with PTS1-sequence showed hypersensitivity to salt. Under salt-stress, T2 transformed plants (HsPECI2) displayed reduced primary root, delayed shoot-growth, and visibly smaller rosette leaves turning pale yellow as compared to the pKYLX71 vector control plant. Also, we found altered reactive oxygen species (ROS) levels and reduced catalase activity in 100 mM sodium chloride (NaCl) treated HsPECI2 transformed plant compared with the pKYLX71 counterpart. ESI-MS/MS data showed that the polar lipids were differentially modulated upon salt treatment in HsPECI2 transformed and pKYLX71 plants as compared with the respective untreated counterpart. Notably, the levels of monogalactosyldiacylglycerol and phosphatidic acid varied significantly, whereas phosphatidylcholine, phosphatidylserine and digalactosyldiacylglycerol contents were moderately upregulated. In parallel, abscisic acid (ABA) responsiveness assay confirmed insensitivity of HsPECI2 transformed plant towards ABA. Overall our data proclaim that HsPECI2 play multifunctional role in normal development and response to salinity stress apart from its primary role in β-oxidation.


2020 ◽  
Vol 21 (23) ◽  
pp. 9065
Author(s):  
Huai-Xia Zhang ◽  
Xiao-Hui Feng ◽  
Jing-Hao Jin ◽  
Abid Khan ◽  
Wei-Li Guo ◽  
...  

Squamosa promoter binding protein (SBP)-box genes are plant-specific transcription factors involved in plant growth and development, morphogenesis and biotic and abiotic stress responses. However, these genes have been understudied in pepper, especially with respect to defense responses to Phytophthora capsici infection. CaSBP11 is a SBP-box family gene in pepper that was identified in our previous research. Silencing CaSBP11 enhanced the defense response of pepper plants to Phytophthora capsici. Without treatment, the expression of defense-related genes (CaBPR1, CaPO1, CaSAR8.2 and CaDEF1) increased in CaSBP11-silenced plants. However, the expression levels of these genes were inhibited under transient CaSBP11 expression. CaSBP11 overexpression in transgenic Nicotiana benthamiana decreased defense responses, while in Arabidopsis, it induced or inhibited the expression of genes in the salicylic acid and jasmonic acid signaling pathways. CaSBP11 overexpression in sid2-2 mutants induced AtNPR1, AtNPR3, AtNPR4, AtPAD4, AtEDS1, AtEDS5, AtMPK4 and AtNDR1 expression, while AtSARD1 and AtTGA6 expression was inhibited. CaSBP11 overexpression in coi1-21 and coi1-22 mutants, respectively, inhibited AtPDF1.2 expression and induced AtPR1 expression. These results indicate CaSBP11 has a negative regulatory effect on defense responses to Phytophthora capsici. Moreover, it may participate in the defense response of pepper to Phytophthora capsici by regulating defense-related genes and the salicylic and jasmonic acid-mediated disease resistance signaling pathways.


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