Abstract
Bacillus velezensis FZB42 is able to activate induced systemic resistance (ISR) to enhance plant defense response against pathogen infections. Though the roles of microRNAs (miRNAs) in Bacillus-triggered ISR have been reported in Arabidopsis, the maize miRNAs responsible for the Bacillus-activated ISR process have not been discovered. To explore the maize miRNAs involved in ISR, maize miRNAs in response to FZB42 (ISR activating), FZB42△sfp△alss (deficient in triggering ISR), and a control for 12 h were sequenced. A total of 146 known miRNAs belonging to 30 miRNA families and 217 novel miRNAs were identified. Four miRNAs specifically repressed in FZB42-treatment were selected as candidate ISR-associated miRNAs. All of them contained at least one defense response-related cis-element, suggesting their potential roles in activating the ISR process. Interestingly, three of the four candidate ISR-associated miRNAs belong to the conserved miR169 family, which has previously been confirmed to play roles in abiotic stress response. Moreover, 52 mRNAs were predicted as potential targets of these candidate ISR-associated miRNAs through TargetFinder software and degradome sequencing. Gene Ontology (GO) and network analyses of target genes showed that these differentially expressed miRNA might participate in the ISR process by regulating nuclear factor Y transcription factor. This study is helpful in better understanding the regulatory roles of maize miRNAs in the Bacillus-activated ISR process.
Highlights
Plant miRNAs with a length of 21–24 nt are non-coding RNA molecules that regulate target mRNA either through transcriptional or translational repression [1]
The roots of maize at the four-leaf stage were first inoculated with B. velezensis FZB42, FZB42 sfp alss, or a control, and the maize leaves were challenge-inoculated with Bipolaris maydis
The results showed that B. velezensis FZB42 reduced the southern corn leaf blight caused by B. maydis, whereas the mutant FZB42 sfp alss, deficient in the production of lipopeptides and 2,3-butanediol, lost the ability to enhance plant defense resistance (Figure 1A and Figure S1)
Summary
Plant miRNAs with a length of 21–24 nt are non-coding RNA molecules that regulate target mRNA either through transcriptional or translational repression [1]. Plant miRNA precursors are firstly transcribed by RNA polymerase II and processed by Dicer-like DCL endonucleases to generate a miRNA/miRNA * duplex. The duplex contains a guide strand (mature miRNA) and a passenger strand (miRNA *) [2]. Plant methyltransferase HUA ENHANCER1 (HEN1) stabilizes the miRNA/miRNA * duplex through 2 -O-methylation. The mature miRNA is separated from the duplex and loaded into an Argonaute (AGO) protein to form the RNA-induced silencing complex (RISC). The RISC is able to cleave target mRNAs which have complement sequences to guide the strand [2]. Some mature plant miRNAs can regulate target genes at protein levels instead of at post-transcriptional levels [3]
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