MiR319-mediated ethylene biosynthesis, signalling and salt stress response in switchgrass

Salinity-induced accumulation of certain microRNAs accompanied by gaseous phytohormone ethylene production has been recognized as a mechanism of plant salt tolerance. MicroRNA319 (miR319) has been characterized as an important player in abiotic stress resistance in some C3 plants, such as Arabidopsis thaliana and rice. However, its role in the dedicated biomass plant switchgrass (Panicum virgatum L.), a C4 plant, has not been reported. Here, we show crosstalk between miR319 and ethylene (ET) for increasing salt tolerance. By overexpressing Osa-MIR319b and a target mimicry form of miR319 (MIM319), we showed that miR319 positively regulated ET synthesis and salt tolerance in switchgrass. By experimental treatments, we demonstrated that ET-mediated salt tolerance in switchgrass was dose-dependent, and miR319 regulated the switchgrass salt response by fine-tuning ET synthesis. Further experiments showed that the repression of a miR319 target, PvPCF5, in switchgrass also led to enhanced ethylene accumulation and salt tolerance in transgenic plants. Genome-wide transcriptome analysis demonstrated that overexpression of miR319 (OE-miR319) down-regulated the expression of key genes in the methionine (Met) cycle but promoted the expression of genes in ethylene synthesis. The results enrich our understanding of the synergistic effects of the miR319-PvPCF5 module and ethylene synthesis in the salt tolerance of switchgrass, a C4 bioenergy plant.