Crosstalk between abscisic acid (ABA) and salicylic acid (SA) regulates susceptibility of tomato to the specialist spider mite Tetranychus evansi Baker & Pritchard

Abstract

In plants, jasmonic acid (JA) is traditionally seen as the key regulator of plant defense against spider mites although indirect evidence suggests that abscisic acid (ABA) might also be involved. This study examined this possibility using an ABA-deficient tomato genotype (notabilis) and the specialist T. evansi which is known to suppress JA-dependent defenses. Wild type cv. Lukullus showed enhanced leaf damage than notabilis, showing that ABA influences susceptibility to specialist spider mites potentially modulating jasmonate levels and dependent defenses. Among the upregulated genes, cv. Lukullus displayed GO enrichment in JA-dependent defense, regulation of ROS production, SA-biosynthesis and the negative regulation of defense whereas in notabilis, these mechanisms were less prominent and all GO terms related to photosynthesis were severely repressed, suggesting that these could be crucial in restricting progression of T. evansi infestation in tomato. At the metabolic level, reduced susceptibility to T. evansi in notabilis accompanied an increased accumulation of free fatty acids and phenylpropanoids mirrored by enhanced gene expression of lipid, phenylpropanoid and lignin metabolic genes as well as genes related to ABA/dehydration and JA signaling. A gene co-expression analysis identified modules correlated with ABA and SA levels which included defense and photosynthesis responses among the up- and downregulated genes, respectively, suggesting their potential crosstalk in the regulation of tomato responses to T. evansi infestation. This extent was further investigated with feeding assays in tomato mutants spr2 (JA-deficient) and NahG (SA-deficient) with T. evansi confirming their role as positive and negative regulators of susceptibility to spider mites, respectively.