几丁质和flg22诱导的辣椒幼苗先天免疫生理响应特征

Characteristics of innate immune physiological response induced by chitin and flg22 in pepper seedlings

【目的】为明确几丁质和鞭毛蛋白衍生肽flg22诱导的辣椒幼苗先天免疫生理响应特征,探讨辣椒先天免疫生理响应与辣椒抗多种病害的关系。【方法】以5个四川本地辣椒品种幼苗为试材,鉴定它们对青枯病和疫病病情指数和抗性水平,采用水培法培育幼苗并进行外源几丁质和flg22处理,检测各品种不同诱导时间下幼苗根系生长、气孔孔径、胼胝质沉积、活性氧(ROS)积累和SOD、CAT活性,以及先天免疫相关基因表达量的变化,综合评价其生理响应及其与抗病性关系。【结果】(1)各品种幼苗青枯病和疫病病情指数以‘川腾10号’最低,抗病性最强,以‘本地条椒’最高,抗病性最弱。(2)外源几丁质和flg22抑制了各品种幼苗根系生长速率,诱导离体叶片气孔闭合,促进叶片细胞壁胼胝质沉积加厚,ROS含量持续增加,SOD和CAT活性不断提高。各品种幼苗先天免疫生理响应指标的平均隶属函数值以‘川腾10号’最高,‘本地条椒’最低,并且平均隶属函数值与疫病、青枯病病情指数均具有显著负相关性。(3)外源flg22和几丁质诱导‘川腾10号’幼苗先天免疫相关基因CaWRKY22、CaMAPK7和ChiIV3显著上调表达。【结论】外源flg22和几丁质可诱导辣椒幼苗先天免疫生理响应,且响应程度强弱在品种间存在差异,依据生理响应指标通过隶属函数可综合评价辣椒品种的抗病水平;‘川腾10号’的平均隶属函数值最高,多抗性水平最好,这与其先天免疫相关基因CaWRKY22、CaMAPK7和ChiIV3的显著上调表达有关。

[Objective]The study aims to examine the characteristics of innate immune physiological responses induced by chitin and flagellin-derived peptide flg22 in pepper seedlings,and to explore the relationship between innate immune physiological responses and pepper multiple resistance to diseases.[Methods]Five local pepper cultivars from Sichuan were used as experimental materials.The disease indexes of bacterial wilt and phytophthora blight in pepper seedlings were analyzed.Seedlings were cultured by hydroponics and treated with chitin and flg22 exogenously.Root growth,stomata aperture,callose deposition,reactive oxygen species(ROS)accumulation,SOD,CAT activities as well as gene expression under different induction times were analyzed.The physiological responses and their relationship with disease resistance were evaluated comprehensively using biostatistics.[Results](1)The lowest disease index of bacterial wilt and phytophthora blight was‘Chuanteng No.10’(‘CT10’)cultivar,which was the strongest in disease resistance.The highest disease index of bacterial wilt and phytophthora blight was‘Tiaojiao’(‘TJ’)cultivar,which was the weakest in disease resistance.(2)Exogenous chitin and flg22 inhibited the root growth rate of pepper seedlings in five cultivars,induced stomatal closure on detached leaves,promoted callose deposition in cell wall,and increased ROS levels with improved SOD and CAT activities.By calculating the average membership function value of the innate immune physiological response,it showed that the highest was‘CT10’and the lowest was‘TJ’.The average membership function value has a significant negative correlation with the disease index of bacterial wilt and phytophthora blight.(3)flg22 and chitin induced the expression of genes involved in innate immune response in‘CT10’,such as CaWRKY22,CaMAPK7,and ChiIV3.[Conclusion]Exogenous flg22 and chitin induce the innate immune physiological responses in pepper seedlings,with variations among the varieties.The average membership function of‘CT10’is the highest and the multi-resistance level is the best,due to the up-regulated expression of CaWRKY22,CaMAPK7,and ChiIV3.