Arabidopsis Kunitz Trypsin Inhibitors in Defense Against Spider Mites

Abstract

Tetranychus urticae (two-spotted spider mite) is a striking example of polyphagy among herbivores with an extreme record of pesticide resistance and one of the most significant pests in agriculture. The T. urticae genome contains a large number of cysteine- and serine-proteases indicating their importance in the spider mite physiology. This work is focused on the potential role of the Kunitz trypsin inhibitor (KTI) family on plant defense responses against spider mites. The molecular characterization of two of these genes, AtKTI4 and AtKTI5, combined with feeding bioassays using T-DNA insertion lines for both genes was carried out. Spider mite performance assays showed that independent KTI silencing Arabidopsis lines conferred higher susceptibility to T. urticae than WT plants. Additionally, transient overexpression of these inhibitors in Nicotiana benthamiana demonstrated their ability to inhibit not only serine- but also cysteine-proteases, indicating the bifunctional inhibitory role against both types of enzymes. These inhibitory properties could be involved in the modulation of the proteases that participate in the hydrolysis of dietary proteins in the spider mite gut, as well as in other proteolytic processes.

Tetranychusevansi spider mite populations suppress tomato defenses to varying degrees

“…This does not imply direct causal relationships between their gene products and spider mite performance. Although expression of PI genes and PI activity, for example, increase upon infestation with defense‐inducing T. urticae (Ataide et al, 2016; Godinho et al, 2016; de Oliveira et al, 2016; Sarmento, Lemos, Bleeker, et al, 2011), and a weak negative correlation between PI activity and T. urticae (but not T. evansi ) performance was observed (de Oliveira et al, 2016), the efficiency of these compounds as digestive inhibitors has been questioned because spider mite guts may lack their enzymatic targets (Arnaiz et al, 2018; Santamaría et al, 2012). Similarly, plant PPOs have been hypothesized to react with plant phenolic compounds in the herbivore gut after ingestion to produce quinones, which subsequently damage enzymes, membranes, and DNA (Constabel & Barbehenn, 2008), thus decreasing herbivore performance.…”

“…In tomato, the induced defense response against spider mites is orchestrated by the plant hormones JA and SA (Ament, Kant, Sabelis, Haring, & Schuurink, 2004; Kant, Ament, Sabelis, Haring, & Schuurink, 2004; Li, Williams, Loh, Lee, & Howe, 2002). These hormones set in motion internal signaling cascades leading to the production of defense‐associated compounds such as proteinase inhibitors (PIs) and polyphenol oxidases (PPO; Arnaiz et al, 2018; Kant et al, 2004; Martel et al, 2015). T. evansi suppress tomato defense downstream of plant hormone accumulation, such that the plant's expression of defense‐associated genes is downregulated to the benefit of the herbivore (Alba et al, 2015; Ataide et al, 2016; Sarmento, Lemos, Bleeker, et al, 2011).…”

Genome-Wide Identification and Expression Analysis of the Protease Inhibitor Gene Families in Tomato

“…Animal Kunitz PIs are extensively studied and proven to be involved in various physiological processes, such as inflammatory processes [59], thrombosis [60], AIDS [61][62][63], and fungal infections [64]. The family has also been studied in different plants, but most of the work is focused on their defenses in insect attacks because their gene expression levels are upregulated by wounds and insect feeding [65]. Notably, the Kunitz family plays an important role against lepidopteran and coleopteran pests in various plants, including poplar [66], rice [67], tomato [68], potato, and tobacco [69].…”

Nipponbare and wild rice species as unexpected tolerance and susceptibility sources againstSchizotetranychus oryzae(Acari: Tetranychidae) mite infestation

“…Among plant defenses, protease inhibitors (PIs) have direct effects on herbivores, interfering with their physiology (Diaz and Santamaria, 2012;Martinez et al 2016;Arnaiz et al 2018). Once ingested by the arthropod, PIs inhibit proteolytic activities, preventing or hindering protein degradation (Terra and Ferreira, 2005).…”

“…Rice has seven Bowman Birk trypsin inhibitor genes, and overexpression of RBBI2-3 in transgenic rice plants resulted in resistance to the fungal pathogen Pyricularia oryzae, indicating that proteinase inhibitors confer in vivo resistance against the fungal pathogen and that they might play a role in the defense system of the rice plant(Qu et al 2003). Recently,Arnaiz et al (2018) verified that Kunitz trypsin inhibitors (KTI) participate in the plant defense responses against the spider mite Tetranychus urticae. Thus, our work is the first to suggest that Bowman Birk trypsin inhibitors may be involved in the tolerance of rice plants against S. oryzae…”