Abstract
ABSTRACTBrachypodium distachyon has recently emerged as a premier model plant for monocot biology, akin to Arabidopsis thaliana. We previously reported genome-wide transcriptomic and alternative splicing changes occurring in Brachypodium during compatible infections with Panicum mosaic virus (PMV) and its satellite virus (SPMV). Here, we dissected the role of Brachypodium phenylalanine ammonia lyase 1 (PAL1), a key enzyme for phenylpropanoid and salicylic acid (SA) biosynthesis and the induction of plant defenses. Targeted metabolomics profiling of PMV-infected and PMV- plus SPMV-infected (PMV/SPMV) Brachypodium plants revealed enhanced levels of multiple defense-related hormones and metabolites such as cinnamic acid, SA, and fatty acids and lignin precursors during disease progression. The virus-induced accumulation of SA and lignin was significantly suppressed upon knockdown of B. distachyon PAL1 (BdPAL1) using RNA interference (RNAi). The compromised SA accumulation in PMV/SPMV-infected BdPAL1 RNAi plants correlated with weaker induction of multiple SA-related defense gene markers (pathogenesis related 1 [PR-1], PR-3, PR-5, and WRKY75) and enhanced susceptibility to PMV/SPMV compared to that of wild-type (WT) plants. Furthermore, exogenous application of SA alleviated the PMV/SPMV necrotic disease phenotypes and delayed plant death caused by single and mixed infections. Together, our results support an antiviral role for BdPAL1 during compatible host-virus interaction, perhaps as a last resort attempt to rescue the infected plant.
Highlights
Brachypodium distachyon has recently emerged as a premier model plant for monocot biology, akin to Arabidopsis thaliana
Genes encoding enzymes putatively involved in plant metabolic and biosynthetic pathways affected by Panicum mosaic virus (PMV) infection were identified using the differential gene expression data and MapMan metabolic pathway analyses [54, 55] (Fig. 1; see Data Set S1 in the supplemental material)
We used Brachypodium and PMV/SPMV as a model pathosystem to gain a broader understanding of the defense-related metabolic pathways perturbed during compatible grass virus infections and the role of B. distachyon PAL1 (BdPAL1) in antiviral defenses
Summary
Brachypodium distachyon has recently emerged as a premier model plant for monocot biology, akin to Arabidopsis thaliana. Another study demonstrated that Arabidopsis bak mutants exhibited increased susceptibility to three RNA viruses (TCV, Tobacco mosaic virus [TMV], and Oilseed rape mosaic virus [ORMV]) during compatible interactions, and crude viral extracts of inoculated leaf tissues induced several PTI markers in a BAK1-dependent manner [5]. These studies showed that BAK1-dependent PTI contributed to host antiviral responses. These and other studies suggest that SA limits virus infection by interfering in multiple steps of viral replication and intercellular spread as well as systemic movement, depending on the virus-host system [14,15,16]
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