Gene expression of salicylic acid and jasmonic acid pathways and photosynthesis parameters of sweet orange trees in response to acibenzolar-S-methyl

Abstract

The use of resistance inducers may be a tool to assist in the management of citrus diseases. However, knowledge about how some inducers, such as the benzothiadiazoles, promote gene expression from the pathways involved in induced resistance and alter plant development are lacking. In this work, we evaluated the effect of the acibenzolar-S-methyl (ASM) on gene expression from the biosynthetic pathways of salicylic (SA) and jasmonic (JA) acids, as well as in physiological parameters of young sweet orange trees. After a single ASM application, gene expression assessed during six time points revealed no significant changes in the main pathway for SA synthesis: isochorismate synthases (ISC) 1 and ICS2 genes were up-regulated only at 6 days after treatment (dat). However, an increase in phenylalanine ammonia lyase (PAL) was observed. Salicylic acid carboxymethyl transferase (BSMT1) and salicylic acid glucosyltransferase I (SAGT1) were up-regulated, indicating expression of genes whose products modify SA. Pointedly up-regulation of lipoxygenase (LOX) and both up- and down-regulation of allene oxide synthase (AOS) and allene oxide cyclase (AOC) in biosynthetic pathways of JA was observed, while jasmonic acid methyl transferase (JMT), whose product modify JA, was consistently induced from three to 13 dat. Besides an increase in SA and JA modification enzymes, ASM reduced photosynthetic rate in treated plants, without affecting the stomatal conductance and the transpiration rate. Our results reveal how the SA and JA pathways are regulated soon after ASM treatment, in particular the up-regulation of BSTM1, SAGT1 and JMT.