THE INNATE IMMUNITY RESPONSES IN RUBBER TREE
Plant innate immunity system consists of two branches: pathogen associated molecular patterns (PAMPs) -triggered immunity (PTI) and effector-triggered immunity (ETI). Two typical pathogen-associated molecular patterns flg22 and chitin from bacteria and fungi were used as inducers to detect the rubber tree immunity response by rubber tree mesophyll protoplast transient expression system. Our data showed that flg22 and chitin induced activation of mitogen-activated protein kinases, generation and accumulation of reactive oxygen species, and transcription of defense genes such as HbPR1 and HbPR5, but not HbMPK3 and HbMPK6. On the other hand, RNA-Seq was used to analyse the transcript abundance in rubber tree after treatment with SA. Based on the KO analysis results, genes encoding BKK1 and FLS2 (flagellin-sensitive 2) which were typical PRR protein and upstream components of the PTI pathway, were rapidly induced. The genes encoding signalling transduction components of the PTI pathway, such as MEKK1, MKKs and some WRKYs, were also upregulated at 6-12 h. The expression of the homologue of PBS1, which functions as a receptor-like cytoplasmic kinase that interacts with the NB-LRR type R protein RPS5 to initiate the advanced ETI response in Arabidopsis was induced quickly. These results indicated that SA can enhance disease resistance in rubber tree by activating both the PTI pathway and PBS1-RPS5-mediated ETI which was analogous to that in Arabidopsis.
Keywords: rubber tree, innate immunity, PTI, ETI, salicylic acid, hevea, disease resistance, gene, signal transduction, SA, chitin, flagellin