Multiple indole glucosinolates and myrosinases defend Arabidopsis againstTetranychus urticaeherbivory

Abstract

Arabidopsis defenses against herbivores are regulated by the jasmonate hormonal signaling pathway, which leads to the production of a plethora of defense compounds, including tryptophan-derived metabolites produced through CYP79B2/CYP79B3. Jasmonate signaling and CYP79B2/CYP79B3 limit Arabidopsis infestation by the generalist herbivore two-spotted spider mite, Tetranychus urticae. However, the phytochemicals responsible for Arabidopsis protection against T. urticae are unknown. Here, using Arabidopsis mutants that disrupt metabolic pathways downstream of CYP79B2/CYP79B3, and synthetic indole glucosinolates, we identified phytochemicals involved in the defense against T. urticae. We show that Trp-derived metabolites depending on CYP71A12 and CYP71A13 are not affecting mite herbivory. Instead, the supplementation of cyp79b2 cyp79b3 mutant leaves with the 3-indolylmethyl glucosinolate and its derived metabolites demonstrated that the indole glucosinolate pathway is sufficient to assure CYP79B2/CYP79B3-mediated defenses against T. urticae. We demonstrate that three indole glucosinolates can limit T. urticae herbivory, but that they have to be processed by the myrosinases to hinder T. urticae oviposition. Finally, the supplementation of the mutant myc2 myc3 myc4 with indole glucosinolates indicated that the transcription factors MYC2/MYC3/MYC4 induce additional indole glucosinolate-independent defenses that control T. urticae herbivory. Together, these results reveal the complexity of Arabidopsis defenses against T. urticae that rely on multiple indole glucosinolates, specific myrosinases, and additional MYC2/MYC3/MYC4-dependent defenses.

Rapid specialization of counter defenses enables two-spotted spider mite to adapt to novel plant hosts

“…Among MYC2,3,4-regulated genes are CYP79B2 and CYP79B3 that are required for the synthesis of Trp-derived secondary metabolites (Figure 1A, (Hull et al ., 2000; Mikkelsen et al ., 2000; Schweizer et al ., 2013). One class of these metabolites are indole glucosinolates, shown to protect Arabidopsis plants against herbivory of a wide range of arthropods, including mites (Elbaz et al ., 2012; Hopkins et al ., 2009; Kim and Jander, 2007; Kim et al ., 2008; Whiteman et al ., 2012; Whiteman et al ., 2011; Widemann et al ., 2021; Zhurov et al ., 2014). The modest increase in fecundity when TSSM fed on cyp79b2 cyp79b3 ( cyp79b2,b3) plants, Figure 1B, indicates that besides indole glucosinolates, there are other MYC2,3,4-regulated defenses that prominently protect Arabidopsis plants against mites.…”

“…However, Arabidopsis -adapted mites, like the ancestral population, performed significantly better on cyp79b2 cyp79b3 than on Col-0 plants, Figure 2B and C, suggesting that mite adaptation to Arabidopsis is not based on the suppression of host defenses. To corroborate the lack of defense suppression in Arabidopsis -adapted mites we determined the expression levels of JA-responsive AOS, MYC2, CYP79B2 , and CYP79B3 genes (labeled in red in Figure 1A) and the abundance of JA, JA-Ile, and indol-3-ylmethylglucosinolate (I3M) (labeled in green in Figure 1A) that were previously established as reliable markers of induced JA-regulated Arabidopsis defenses against mite herbivory (Widemann et al ., 2021; Zhurov et al ., 2014). The expression levels and the abundance of defense-associated markers were determined in Col-0 plants that were challenged with bean-a, cyp -a, or Col-a mites after 24 h of mite herbivory.…”

“…The prevalence of the ability to suppress plant responses across tomato-adapted T. urticae populations is currently not known, nor is its presence in other T. urticae host-adapted populations. Even though the interference with either JA-biosynthesis or its signalling could have been an effective way to attenuate a whole range of Arabidopsis defense compounds, (Figure 1, (Widemann et al ., 2021; Zhurov et al, 2014 )), our data suggest that Arabidopsis -adapted mites did not interfere with JA-regulated Arabidopsis defenses. Arabidopsis -adapted mites, just like the ancestral bean-a population, had greater fitness on cyp79b2 cyp79b3 than on Col-0 plants (Figure 2).…”

“…Aliphatic glucosinolates are ineffective in restricting mite herbivory (Zhurov et al ., 2014). Instead, the antifeedant effects of indole glucosinolates on T. urticae have been recently characterized (Widemann et al ., 2021), raising a possibility that Arabidopsis defensive indole glucosinolate breakdown products may be detoxified by mite adaptation-associated GST(s).…”

“…Fecundity over two days of bean-a mites on Col-0, cyp79b2 cyp79b3 , and myc2 myc3 myc4 , and fecundity over six days of bean-a, cyp -a, and Col-a mites on cyp79b2 cyp79b3 or Col-0 Arabidopsis plants were assessed as previously described (Widemann et al ., 2021). The experiment included five to ten biological replicates for each treatment that were repeated in three experimental trials.…”