Study On The Molecular Mechanism Of Arabidopsis SR1 Gene Involved In Plant Response To Deficient Ca And Excess Mn

SR1(Signal-responsive 1)is calmodulin-binding transcription activator(CAMTA)which can bind with the calmodulin Ca M(Calmodulin).Ca M is a Ca²⁺sensor.When plants were stimulated,the concentration of cytoplasmic Ca²⁺([Ca²⁺]cyt)increases.When Ca²⁺bind with Ca M,Ca M configuration will change which lead to Ca M to interact with downstream effector.The change of effector affinity regulates the downstream defense response.It is reported that SR1 is involved in regulating the response of plants to pathogens.The gain-of-function mutant sr1-4D has enhanced disease resistance,but loss-of-function mutant sr1-1 and sr1-2 has enhanced disease sensitivesity.In this study,the gain-of-function mutants sr1-4D and loss-of-function mutants sr1-1 and sr1-2 of Arabidopsis SR1(AtSR1)gene were treated with excess or deficient mineral elements.We found that sr1-4D has anti-deficient Ca(0 m M Ca)and anti-excess manganese(10×Mn,450?M)phenotype.In order to explore how the SR1 gene participates in the response of plants to deficient Ca and excess Mn stress respectively,it was found that sr1-4D can resist the oxidative damage and cell death induced by excess Mn stress by histochemical staining.Through transcriptome analysis,34 genes up-regulated and 53 genes down-regulated in sr1-4D compared with Col-0.The up-regulated genes include AT2G15680 and AT1G66400 genes encoding calmodulin,and AT4G30290 genes encoding xyloglucan endotransglucosylase/hydrolase(xyloglucan endotransglucosylase/hydrolase,XTH).It is found that the XTH enzyme activity of sr1-4D was enhanced under deficient Ca and excess Mn condtion.The content of Ca and Mn is determined by Inductively Coupled Plasma Optical Emission Spectrometer(ICP-OES)and it is found that total Ca content and total Mn content in leaf and root were similar to Col-0 under deficient Ca and excess Mn.The cell wall Ca content were similar to Col-0,however the cell wall Mn content sr1-4D is significantly lower than that of Col-0.IQ1 domains of SR1 and SR1-4D proteins could not bind to Ca²⁺and Mn²⁺by Isothermal Titration Calorimetry.This study shows that SR1 is involved in regulating the response of plants to deficient Ca and excess Mn,IQ1 domains does not combine with Ca²⁺and Mn²⁺.It is probably that SR1 regulate XTH to modify the cell wall and affect the accumulation of Mn in the cell wall which induced to plant adapt the excess Mn condition.Through calmodulin and XTH regulated by SR1 to improve plant adaption to deficicient Ca condition.The regulation mechanism of SR1 is also unclear which needs further study.