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

Abstract

Abstract [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.

Keywords

• capsicum annuum l.
• plant innate immunity
• pamps
• flg22
• chitin
• physiological response