# Distinct Signatures of Host Defense Suppression by Plant-Feeding Mites
## 2 Results
### Transcriptomic Profiles
#### 2.2.2 Detailed Analysis of Selected Defense-Associated Pathways
thaliana_ NONEXPRESSOR OF PATHOGENESIS-RELATED GENES \(1\) (NPR1) was induced to similar levels in response to all mite-infestation treatments, except for the _T. evansi_ infestation (Figure 4). A putative homolog of _A. thaliana_ NPR3/4 (Solyc07g044980) had the same expression pattern. With regard to TGA transcription factors, we found one _TGA_ gene to be down-regulated in Tu+Te, Tu, Tu+Al and Al, most strongly so in the latter two samples. In sharp contrast with the SA biosynthesis, metabolism or signaling genes, we found massive changes in the expression of downstream defense-associated genes (Figure 4). Most SA-responsive genes associated with plant immunity code for so-called pathogenesis-related (PR) proteins that commonly have, or are predicted to have, antimicrobial and/or insecticial properties [78]. The general picture that emerged from our microarray analysis of SA defense response marker genes is as follows: (i) The expression of dozens of genes encoding PR-proteins of various classes was highly induced in Tu and Al, often to the same extent, but was not induced in Te. (ii) Compared with the Tu and Al single infestations, in dual-infested leaves the number of up-regulated genes as well as the magnitude of their induction was higher in Tu+Al, while both factors were lower in Tu+Te (Figure 4). Using qPCRs, we verified these typical expression profiles for some SA marker genes (Figure S1I-J). Our results corroborate the report by [PERSON] et al. [23] that _T. urticae_ and _A. lycopersici_ each induce SA-mediated defense responses and these are additive when mites from both species simultaneously infest the same leaflet. In line with the data of [PERSON] et al. [33], our results also indicate that _T. evansi_ suppresses SA defenses. In more detail: we found that for roughly 50% of the surveyed SA defense marker genes the magnitude of up-regulation was considerably lower (i.e., absolute Log\({}_{2}\)FCdifference > 0.2) in Tu+Te than in Tu samples, with five of them being among the top-31 candidate _T. evanisi_-suppressed genes (Table 2). This suppression was confirmed with qPCRs (Figure S1I-J). Figure 4: Gene-expression heat map depicting the relative transcript levels of tomato (_Solanum lycopersicum_) genes that encode proteins with a (predicted) function in the salicylic acid (SA) pathway  
and that were differentially expressed in leaves after seven days of infestation with herbivorous mites. Tomato leaves were infested with either a single mite species (_Tetranychus urticae_ (Tu), _Tetranychus evansi_ (Te), or _Aculops lycopersici_ (Al)) or two species simultaneously (_T. urticae_ plus _T. evansi_ (Tu+Te), or _T. urticae_ plus _A. lycopersici_ (Tu+Al)). Non-infested plants served as controls and were used as a common reference in the transcriptional comparisons. Presented genes were differentially expressed ([PERSON] and [PERSON] false discovery rate adjusted \(p\leq 0.05\); Log\({}_{2}\) fold change (FC) \(\geq 0.585\)) in at least one of the mite-infestation treatments. The different (sub)sections of the pathway are specified on the left. Dark green squares in the leftmost column denote that transcription of the respective gene was found to be significantly induced in the tomato jasmonic acid (JA)-biosynthesis mutant _def-1_, 24 h after exogenous application of JA (for details see [39]). The light green square denotes JA-inducibility of the respective gene according to [75].