Abstract
With global warming, high temperature stress has become a main threat to the growth of cool-season turfgrasses, including perennial ryegrass. As one of the conserved plant microRNA families, miR408s are known to play roles in various abiotic stresses, including cold, drought, salinity, and oxidative stress, but no report, thus far, was found for heat. Here, perennial ryegrass plants overexpressing rice Os-miR408 were used to investigate the role of miR408 in plant heat tolerance. Both wild type (WT) and miR408 transgenic perennial ryegrass plants (TG) were subjected to short-term heat stress at 38 °C for 72 h (experiment 1) or at 42 °C for 48 h (experiment 2), and then let recover for 7 days at optimum temperature. Morphological changes and physiological parameters, including antioxidative responses of TG and WT plants, were compared. The results showed that miR408 downregulated the expression of two putative target genes, PLASTOCYANIN and LAC3. Additionally, overexpression of Os-miR408 improved thermo-tolerance of perennial ryegrass, demonstrated by lower leaf lipid peroxidation and electrolyte leakage, and higher relative water content after both 38 and 42 °C heat stresses. In addition, the enhanced thermotolerance of TG plants could be associated with its morphological changes (e.g., narrower leaves, smaller tiller angles) and elevated antioxidative capacity. This study is the first that experimentally reported a positive role of miR408 in plant tolerance to heat stress, which provided useful information for further understanding the mechanism by which miR408 improved plant high-temperature tolerance, and offered a potential genetic resource for breeding heat-resistant cool-season turfgrass in the future.
Highlights
Environmental stress, including heat, is one of the major factors restricting agricultural production worldwide
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These indicated that the two genes could be involved in the regulation of morphological changes and heat stress responses observed in the transgenic perennial ryegrass plants
Summary
Environmental stress, including heat, is one of the major factors restricting agricultural production worldwide. Perennial ryegrass (Lolium perenne L.) is a widely grown cool-season turf and forage grass species in the world It has many desirable agronomic traits, including dark green color, rapid growth and establishment, good turf quality, and high yield as a forage grass under favorable growth and environmental conditions. As a perennial coolseason grass, it performs best at a temperatures ranging from 15 to 25 ◦C, and the growth usually begins to decline as the temperature goes beyond 27 ◦C It cannot withstand hightemperature weather, and heat stress is a main factor limiting its growth and development in transition and warmer regions [3]. Plant microRNAs (miRNAs) are a group of small non-coding RNAs at the length of about 19 to 25 nucleotides They function in post-transcriptional regulation of gene expression and RNA silencing via base pairing to complementary sequences within target mRNA molecules [4]. Knowledge generated in this study will contribute valuable information towards understanding the role of miR408 in plant responses to heat stress, perhaps leading to breeding more thermotolerant perennial ryegrass for transitional and southern regions
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