Abstract
Compounds that establish induced resistance (IR) in plants are promising alternatives for the pesticides that are progressively being banned worldwide. Screening platforms to identify IR-establishing compounds have been developed, but none were specifically designed for monocot plants. Here, we propose the use of an RT-qPCR screening platform, based on conserved immunity marker genes of rice as proxy for IR induction. Central regulators of biotic stress responses of rice were identified with a weighted gene co-expression network analysis (WGCNA), using more than 350 microarray datasets of rice under various sorts of biotic stress. Candidate genes were narrowed down to six immunity marker genes, based on consistent association with pattern-triggered immunity (PTI), both in rice plants as in rice cell suspension cultures (RCSCs). By monitoring the expression of these genes in RCSCs upon treatment with candidate IR-inducing compounds, we showed that our marker genes can predict IR induction in rice. Diproline, a novel IR-establishing compound for monocots that was detected with these marker genes, was shown to induce rice resistance against root-knot nematodes, without fitness costs. Gene expression profiling of the here-described PTI-marker genes can be executed on fully-grown plants or in RCSCs, providing a novel and versatile tool to predict IR induction.
Highlights
As sessile organisms, plants are highly susceptible for biotic and abiotic stressors
By monitoring the expression of these genes in rice cell suspension cultures (RCSCs) upon treatment with candidate induced resistance (IR)-inducing compounds, we showed that our marker genes can predict IR induction in rice
Based on the approximate scale-free topology criterion and the mean connectivity k, the power β was set to an optimal value of 6 (Supplementary Information 3)
Summary
Plants are highly susceptible for biotic and abiotic stressors. A limited number of in planta screening platforms to screen for IR-inducing compounds have been proposed [20,21,22], but none have been developed for monocot plants, whose immune system shows divergence from those of dicot plants [23]. We hypothesized that transcriptional induction of PTI-marker genes could be used as screening strategy to identify IR-inducing compounds. Key regulators of the biotic stress response of rice were identified in silico via a weighted gene co-expression network analysis (WGCNA). Since the rationale of the hereby-presented study was that induction of PTI genes could be used as a screening strategy for IR-inducing compounds, PTI-responsive genes were selected, via both in planta and in vitro validation. We showed that diproline, a less-described compound detected as IR-inducing by our platform, can effectively and efficiently lower rice susceptibility against the root-knot nematode Meloidogyne graminicola
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