Overexpression of Sly-miR398b Compromises Disease Resistance against through Regulating ROS Homeostasis and JA-Related Defense Genes in Tomato.

MicroRNAs (miRNAs) have been shown to be critical components in plant immunity. MicroRNA398 (miR398) is a highly conserved miRNA in all land plants and plays crucial roles in diverse biotic stress responses. However, the role of miR398 has not yet been characterized in tomato resistance against . In this report, the transcript levels of sly-miR398b were strongly decreased in -infected leaves and the overexpression of sly-miR398b resulted in enhanced susceptibility. The attenuated expression of (), (), and (), as well as the decreased activities of superoxide dismutase (SOD) and GPOD, collectively led to increased hydrogen peroxide (HO) accumulation in sly-miR398b overexpressing plants. Furthermore, sly-miR398b was induced by methyl jasmonate (MeJA) treatment. The overexpression of sly-miR398b suppressed the expression of , , and in response to and MeJA treatment. Our data demonstrate that sly-miR398b overexpression negatively regulates the resistance to in tomato by inducing the accumulation of reactive oxygen species (ROS) and downregulating the expression of MeJA-responsive defense genes.