Effect Of Ecological Factors On Jasmonates Content And Biosynthetic Genes Expression Of Tea Plants (Camellia Sinensis L.)

Jasmonates（JAs）are an important phytohormone for plant resistance to adversity stress and affects both plant growth and photosynthetic capacity,including jasmonic acid（JA）,methyl jasmonate（Me JA）,JA-isoleucine（JA-Ile）,12-oxo-phytodienoic acid（OPDA）,etc.In this paper,we used Camellia Sinensis（L.）O.Kuntze cv.Huangdan as the test material to study the response patterns of JA,JA-Ile,Me JA,OPDA and their biosynthesis genes to air temperature,air relative humidity,substrate relative humidity and photosynthetically active radiation in an artificial climate chamber,and then analyzed the correlation between JAs content and photosynthetic characteristics and growth indexes in tea plants.We aimed to explore the molecular mechanism of JAs biosynthesis regulated by different ecological factors,and to explore the key ecological factors affecting the impact of JAs biosynthesis in tea plants.The main findings of this study are as follows1.Response of JAs content in tea plants to air temperature and its molecular mechanismTea plants were treated with different air temperatures at 15℃,20℃,25℃and 30℃.The results showed that JA,JA-Ile and Me JA had the highest content at 20℃,OPDA had the highest content at 15℃,and the content of JAs decreased significantly at 30℃treatment.According to Pearson correlation analysis,The expression of Cs LOX2S-1,Cs LOX2S-2,Cs AOS2,Cs AOC1,Cs AOC2,Cs OPR,Cs JAR,Cs JAZ2,Cs MYC2a,Cs MYC2b and other genes were positively correlated with the contents of JA,JA-Ile and Me JA,and the expression of Cs JAZ1,Cs MYC2c were positively correlated with OPDA content,that is,Cs LOX2S-1,Cs LOX2S-2,Cs AOS2,Cs AOC1,Cs AOC2 positively regulated the synthesis of OPDA,and then Cs OPR positively regulated the conversion of OPDA to JA,and under the action of Cs JAR,JA is further converted into a more biologically active JA-Ile.The co-expression network analysis showed that there was a co-expression trend of receptor protein（Cs JAZ2）,transcription factors（Cs MYC2a,Cs MYC2b）and structural genes（Cs LOX2S-1,Cs LOX2S-2,Cs AOS2,Cs AOC1,Cs AOC2,Cs OPR,Cs JAR）under air temperature treatment.JA,JA-Ile and Me JA contents are significantly negatively correlated with transpiration rate,intercellular CO₂ concentration,and stomatal conductance,and are significantly positively correlated with water use efficiency,effective photochemical quantum yield of PSⅡphotosynthetic and rate of electronic transmission of photosynthesis.There was a negative correlation between the contents of JAs and the growth of tea plants.2.Response of JAs content in tea plants to air relative humidity and its molecular mechanismTea plants were treated with different air relative humidity of 40%,50%,70%and 90%.The results showed that the low air relative humidity condition of 40%could significantly induce JAs synthesis,and JAs did not differ significantly under the three treatments of 50%,70%and 90%.According to the Pearson correlation analysis,the contents of JA,JA-Ile,Me JA and OPDA had a significant positive correlation with the expression of the 15 JAs biosynthesis genes in this study.That is,under the treatment of 40%air relative humidity,Cs LOX1,Cs LOX2S-1,Cs LOX2S-2,Cs AOS1,Cs AOS2,Cs AOC1 and Cs AOC2 positively regulated the synthesis of OPDA,and the expression of Cs OPR promoted the conversion of OPDA to JA.and under the action of Cs JAR and Cs JMT,JA was further converted to the more bioactive JA-Ile and Me JA.Co-expression network analysis showed that there were co-expression trends of receptor proteins（Cs JAZ1,Cs JAZ2）,transcription factors（Cs MYC2a,Cs MYC2b,Cs MYC2c）and structural genes（Cs LOX1,Cs LOX2S-1,Cs LOX2S-2,Cs AOS2,Cs AOC2,Cs OPR,Cs JAR,Cs JMT）.The JAs content of tea plants was overall negatively correlated with photosynthetic parameters and chlorophyll fluorescence parameters.JAs showed a significant negative correlation with tea tree growth indicators overall,especially with root,shoot and leaf growth.3.Response of JAs content in tea plants to substrate relative humidity and its molecular mechanismThe results of different substrate relative humidity treatments on tea plants at 55%,65%,75%and 85%showed that the JAs content increased significantly at 55%and 85%treatments.This indicates that JAs responded strongly to both too high and too low substrate relative humidity.According to Pearson correlation analysis,Cs JAZ2,Cs MYC2b,Cs MYC2c gene expression was significantly positively correlated with JA,JA-Ile,Me JA content,Cs LOX1,Cs JMT,Cs LOX2S-1 gene expression was significantly positively correlated with JA,Me JA content,Cs LOX1,Cs AOS2,Cs AOC1 gene expression was positively correlated with OPDA content.Under the conditions of substrate relative humidity of 55%and85%,Cs LOX1,Cs LOX2S-2 and Cs AOC1 positively regulated the synthesis of OPDA,Cs OPR was weak in promoting the conversion of OPDA to JA,Cs JAR,Cs JMT promoted further conversion of JA to JA-Ile,Me JA.Co-expression network analysis showed that there was a co-expression trend of receptor protein（Cs JAZ1）,transcription factors（Cs MYC2a,Cs MYC2b,Cs MYC2c）and structural genes（Cs LOX1,Cs LOX2S-2,Cs JAR,Cs JMT）.JA,JA-Ile,Me JA content have a significant positive correlation with net photosynthetic rate,Me JA is also significantly positively correlated with water use efficiency,Me JA and OPDA were negatively correlated with potential photochemical efficiency of PSII,maximum photochemical efficiency of PSII,effective photochemical quantum yield of PSⅡphotosynthetic,and rate of electronic transmission of photosynthesis.JA and JA-Ile were positively correlated with leaf length,OPDA was negatively correlated with growth indexes,and significantly negatively correlated with shoot diameter and leaf thickness.4.Response of JAs content in tea plant to photosynthetically active radiation and its molecular mechanismDifferent photosynthetically active radiation treatments of 150,250,350,450 and 550μmol·m^-2·s^-1 were applied to tea plants.The results showed that the content of JAs increased significantly at low light intensity and decreased gradually with the increase of photosynthetically active radiation.According to Pearson correlation analysis,Cs MYC2b gene expression was positively correlated with JA,JA-Ile,Me JA and OPDA contents.The co-expression network analysis showed that there was a co-expression trend of receptor protein（Cs JAZ1）,transcription factors（Cs MYC2a,Cs MYC2b,Cs MYC2c）and structural genes（Cs LOX2S-2,Cs AOS1）under photosynthetically active radiation treatment.Me JA and OPDA contents were highly significantly positively correlated with transpiration rate and stomatal conductance,OPDA was also highly significantly positively correlated with net photosynthetic rate,tea tree JAs contents were positively correlated with effective photochemical quantum yield of PSⅡphotosynthetic,and rate of electronic transmission of photosynthesis,and the JA and JA-Ile were also have a significant positive correlation with potential photochemical efficiency of PSII and maximum photochemical efficiency of PSII.The content of JAs was negatively correlated with the growth of tea plants,and was significantly negatively correlated with root growth.5.Key ecological factors affecting JAs biosynthesis in tea plantsThe changes of JAs content in tea plants under different ecological factors were analyzed,and air temperature had the most significant effect on JAs content in tea plants.Kaiser analysis calculated the comprehensive score of the effect of different ecological factors on JAs content and gene expression.The results showed that the air temperature 20℃,25℃,15℃treatment scores ranked the top three.Comprehensive analysis showed that air temperature treatment is a key ecological factor affecting the biosynthesis of JAs.