Mechanisms Of Arabidopsis SYP71 And SYP81 Regulating Cell Wall Biosynthesis And Stress Response

Intracellular and intercellular material exchange in plants is mainly accomplished by vesicle transport.The process of vesicle transport includes budding,directional movement,tethering,anchoring and membrane fusion.The anchoring and membrane fusion are mainly mediated by the SNARE（soluble N-ethylmaleimide-sensitive factor attachment protein receptor）proteins.SNARE-mediated vesicle transport is essential for plant growth and development and environmental adaptation.Qa-SNARE AtSYP81 is localized on the endoplasmic reticulum（ER）.In addition to mediating vesicular transport between the Golgi and the ER,AtSYP81 regulates peroxisome formation and ROS homeostasis in plant cells.Qc-SNARE AtSYP71 has multiple localizations,including the ER,plasma membrane（PM）,and endosome and cell plate,and plays an important regulatory role in the formation of cell plates during cytoplasmic division.Moreover,AtSYP81 and AtSYP71 interact with each other.To explore the correlation between the functions of AtSYP81 and AtSYP71,single mutants atsyp71-3,atsyp81-1 and double mutant atsyp71-3 atsyp81-1 were used to conduct a preliminary study on the regulatory mechanisms of AtSYP71 and AtSYP81 on ROS homeostasis,stress response and cell wall biosynthesis in plants.The results are as follows:1.AtSYP71 and AtSYP81 interact with each other and play a synergistic regulatory role in vesicle trafficking.Early development of atsyp71-3,atsyp81-1 and atsyp71-3 atsyp81-1were inhibited,while the phenotype of double mutant became worse,indicating that both AtSYP71 and AtSYP81 synergistically regulate plant growth and development.2.Compared with wild type,there were significant changes in the auxin level in the root tips of the mutant seedlings,however,the change trend in atsyp71-3 and atsyp81-1 was opposite,indicating that the short roots were due to growth inhibition caused by significant changes of auxin concentration in root tips,but the regulatory mechanisms of AtSYP71 and AtSYP81 are different.3.The ROS levels in roots of atsyp71-3,atsyp81-1 and atsyp71-3 atsyp81-1 seedling showed significant changes,with the double mutant being more prominent.When treated with H₂O₂,the wild-type root length became shorter,but that of atsyp71-3,atsyp81-1 and atsyp71-3atsyp81-1 increased siginificnatly,with atsyp81-1 more prominent.These results indicate that both AtSYP71 and AtSYP81 regulate ROS homeostasis in plants.4.When treated with NaCl,the root length of atsyp71-3 significantly increased,while that of atsyp81-1 and the double mutant showed the same trend as the wild-type,both of which became shorter.When treated with Na HCO₃,as the concentration increased,the wild-type root length gradually decreased,while the atsyp81-1 root length slightly increased under 1 m M Na HCO₃ treatment.As the concentration increased,the root gradually shortened.However,under different concentrations of Na HCO₃ treatment,the root length of both atsyp71-3 and the double mutant significantly increased.These suggest that both AtSYP71 and AtSYP81 regulate salt and alkali stress response,but the regulatory mechanisms are different.5.Under pH8 condition,the root length of wild-type and atsyp81-1 were significantly shorter than that under p H5.8,but that of atsyp71-3 and double mutant were significantly longer than that under p H5.8.Application of p H buffer MES at p H7 and 8 caused significant restoration of root length in atsyp71-3 and the double mutant.These results indicate that both AtSYP71 and AtSYP81 regulates p H homeostasis,but the regulatory mechanisms are different.6.The Transcriptome analysis of roots of atsyp81-1 and atsyp71-3 indicate that differentially expressed genes（DEGs）were mainly enriched in cell wall biosynthesis and remodeling related pathways.The cross section observation revealed that the stem diameter of atsyp71-3 did not show significant changes compared with that of wild-type,but that of atsyp81-1 and the double mutant significantly decreased.The cell wall structure and lignin content of the mutants showed significant changes,but the phenotypes of atsyp71-3 and atsyp81-1 were opposite.These results indicate that the regulatory mechanisms of AtSYP71and AtSYP81 on cell wall biosynthesis are different.In summary,both AtSYP71 and AtSYP81 regulate plant growth and stress response,but their regulatory mechanisms are different.AtSYP81 directly regulates ROS homeostasis by controling peroxisome generaion,while AtSYP71 may regulate plant growth and environmental stress response via regulating pH homeostasis.