Phenylalanine metabolism serves as an important route for the production of diverse secondary metabolites including phenylpropanoids. The phenylpropanoid pathway is involved in plant immunity, but whether it can regulate rhizobacteria-induced resistance is poorly understood. In this study, we confirmed a growth-promoting rhizobacterium strain JR48 could induce resistance, strengthen salicylic acid (SA) signaling, and increase lignin content during Phytophthora capsici infection. We conducted transcriptome sequencing to analyze the effect of JR48 on the expression of pepper (Capsicum annuum L.) genes, generated transgenes and loss-of-function genetic materials to specify the function of peroxidase genes, and implemented metabolomics analysis to uncover the resistance-inducing metabolites of JR48. JR48 activated expression of several pepper peroxidase genes in the phenylpropanoid pathway during pathogen infection. These peroxidases positively regulated lignification-mediated pathogen resistance, and the phenylpropanoid pathway acted downstream of SA signaling to confer JR48-induced resistance. Further, JR48 was capable of producing phenylpyruvate to enhance phenylalanine accumulation, thereby reinforcing phenylalanine metabolism-dependent lignification and resistance. Our results revealed that JR48 produces phenylpyruvate to refuel phenylalanine metabolism and reinforces SA signaling to further activate expression of peroxidase genes. This study uncovers immune components previously hidden in metabolic pathways and a recent mechanism underlying rhizobacteria-induced plant resistance.

The biological function of RNA can be modulated by base modifications. Here, we unveiled the occurrence of N4-acetylation of cytidine in plant RNA, including mRNA, by employing LC-MS/MS and acRIP-seq. We identified 325 acetylated transcripts from the leaves of four-week-old Arabidopsis (Arabidopsis thaliana) plants and determined that two partially redundant N-ACETYLTRANSFERASEs FOR CYTIDINE IN RNA (ACYR1 and ACYR2), which are homologous to mammalian NAT10, are required for acetylating RNA in vivo. A double null-mutant was embryo lethal, while eliminating three of the four ACYR alleles led to defects in leaf development. These phenotypes could be traced back to the reduced acetylation and concomitant destabilization of the transcript of TOUGH, which is required for miRNA processing. These findings indicate that N4-acetylation of cytidine is a modulator of RNA function with a critical role in plant development and likely many other processes.

Xanthomonas campestris pv. campestris (Xcc)-induced black rot is one of the most serious diseases in cruciferous plants. Using beneficial microbes to control this disease is promising. In our preliminary work, we isolated a bacterial strain (JR48) from a vegetable field. Here, we confirmed the plant-growth-promoting (PGP) effects of JR48 in planta, and identified JR48 as a Priestia megaterium strain. We found that JR48 was able to induce plant resistance to Xcc and prime plant defense responses including hydrogen peroxide (H₂O₂) accumulation and callose deposition with elevated expression of defense-related genes. Further, JR48 promoted lignin biosynthesis and raised accumulation of frees salicylic acid (SA) as well as expression of pathogenesis-related (PR) genes. Finally, we confirmed that JR48-induced plant resistance and defense responses requires SA signaling pathway. Together, our results revealed that JR48 promotes plant growth and induces plant resistance to the crucifer black rot probably through reinforcing SA accumulation and response, highlighting its potential as a novel biocontrol agent in the future.