Overexpression of Rice microRNA319 Improves Thermotolerance of Perennial Ryegrass.

Heat stress is a major problem affecting the growth of cool-season turfgrasses in transition zone and warmer regions, e.g. perennial ryegrass (Lolium perenne L.). MicroRNA319 (miR319) was found to be involved in both plant development and plant responses to various abiotic stresses, including drought, salinity, and cold. However, it is unclear if overexpression of miR319 affects plant heat tolerance. And our greenhouse observation found miR319 transgenic perennial ryegrass plants seemed to have better thermo-tolerance than WT plants. Our objective was to investigate if the constitutive expression of miR319 could enhance the thermo-tolerance in perennial ryegrass and the possible physiological and molecular mechanism underneath. Our results showed that overexpression of miR319 gene resulted in wider leaf blades in perennial ryegrass. Moreover, under both short-term (27 h, 42 ℃) and long-term (9 day, 35 ℃) high temperature treatments, transgenic perennial ryegrass plants showed enhanced heat stress tolerance compared to the wild type plants as manifested by better grass quality, lower shoot electrolyte leakage (50% lower than that of wild type plants), and higher relative leaf water content. Whole genome transcriptional analysis found that some genes related to antioxidative system, stress responsive transcription factors (NAC, HSF, e.g.) and Jasmonic acid biosynthesis were altered in transgenic plants under both control and heat stress conditions. In a summary, our findings of the study demonstrate that miR319 plays an important role in transgenic perennial ryegrass response to heat stress, which may result from the enhanced antioxidative system and others stress responsive genes.