Tomato DCL2b is required for the biosynthesis of 22-nt small RNAs, the resulting secondary siRNAs, and the host defense against ToMV. Issue 1 (1st September 2018) - Wang, Tian
Abstract: The tomato encode four functional DCL families, of which DCL2 is poorly studied. Here, we generated loss-of-function mutants for a tomato DCL2 gene, dcl2b, and we identified its major role in defending against tomato mosaic virus in relation to both natural and manual infections. Genome-wide small RNA expression profiling revealed that DCL2b was required for the processing 22-nt small RNAs, including a few species of miRNAs. Interestingly, these DCL2b -dependent 22-nt miRNAs functioned similarly to the DCL1 -produced 22-nt miRNAs in Arabidopsis and could serve as triggers to generate a class of secondary siRNAs. In particular, the majority of secondary siRNAs were derived from plant defense genes when the plants were challenged with viruses. We also examined differentially expressed genes in dcl2b through RNA-seq and observed that numerous genes were associated with mitochondrial metabolism and hormone signaling under virus-free conditions. Notably, when the loss-of-function dcl2b mutant was challenged with tomato mosaic virus, a group of defense response genes was activated, whereas the genes related to lipid metabolism were suppressed. Together, our findings provided new insights into the roles of tomato DCL2b in small RNA biogenesis and in antiviral defense. Short sequences provide pathogen protection: A protein that processes gene-regulating RNA molecules helps defend tomato plants against viral infections. The various DCL proteins play a prominent role in processing tiny RNAs known as microRNA and short interfering RNA, which in turn modulate gene activity. Researchers led by Hongliang Zhu at China Agricultural University set out to study a DCL protein produced by tomatoes that remains poorly defined from a functional perspective. The researchers did not notice any prominent abnormalities when they genetically manipulated plants to eliminate expression of the DCL2b gene. However, these DLC2b -deficient plants proved disproportionately vulnerable to tomato mosaic virus, with infection producing striking developmental defects. Zhu and colleagues determined that loss of this gene disrupts processing of a subset of regulatory RNAs that may help mediate the plant antiviral response.