Integrated physiological and transcriptomic analyses of two warm- and cool-season turfgrass species in response to heat stress

miRNAs and Their Target Genes Play a Critical Role in Response to Heat Stress in Cynodon dactylon (L.) Pers

Annual global temperature is increasing rapidly. Therefore, in the near future, plants will be exposed to severe heat stress. However, the potential of microRNAs-mediated molecular mechanism for modulating the expression of their target genes is unclear. To investigate the changes of miRNAs in thermo-tolerant plants, in this study, we first investigated the impact of four high temperature regimes including 35/30 °C, 40/35 °C, 45/40 °C, and 50/45 °C in a day/night cycle for 21 days on the physiological traits (total chlorophyll, relative water content and electrolyte leakage and total soluble protein), antioxidant enzymes activities (superoxide dismutase, ascorbic peroxidase, catalase and peroxidase), and osmolytes (total soluble carbohydrates and starch) in two bermudagrass accessions named Malayer and Gorgan. The results showed that more chlorophyll and the relative water content, lower ion leakage, more efficient protein and carbon metabolism and activation of defense proteins (such as antioxidant enzymes) in Gorgan accession, led to better maintained plant growth and activity during heat stress. In the next stage, to investigate the role of miRNAs and their target genes in response to heat stress in a thermo-tolerant plant, the impact of severe heat stress (45/40 °C) was evaluated on the expression of three miRNAs (miRNA159a, miRNA160a and miRNA164f) and their target genes (GAMYB, ARF17 and NAC1, respectively). All measurements were performed in leaves and roots simultaneously. Heat stress significantly induced the expression of three miRNAs in leaves of two accession, while having different effects on the expression of these miRNAs in roots. The results showed that a decrease in the expression of the transcription factor ARF17, no change in the expression of the transcription factor NAC1, and an increase in the expression of the transcription factor GAMYB in leaf and root tissues of Gorgan accession led to improved heat tolerance in it. These results also showed that the effect of miRNAs on the modulating expression of target mRNAs in leaves and roots is different under heat stress, and miRNAs and mRNAs show spatiotemporal expression. Therefore, the simultaneous analysis of miRNAs and mRNAs expressions in shoot and roots is needed to comprehensively understand miRNAs regulatory function under heat stress.

Response of Warm Season Turf Grasses to Combined Cold and Salinity Stress under Foliar Applying Organic and Inorganic Amendments

Turfgrasses are considered an important part of the landscape and ecological system of golf courses, sports fields, parks, and home lawns. Turfgrass species are affected by many abiotic stresses (e.g., drought, salinity, cold, heat, waterlogging, and heavy metals) and biotic stresses (mainly diseases and pests). In the current study, seashore paspalum (Paspalum vaginatum Sw.) and Tifway bermudagrass (Cynodon transvaalensis Burtt Davy × C. Dactylon) were selected because they are popular turfgrasses frequently used for outdoor lawns and sport fields. The effect of the combined stress from both soil salinity and cold on these warm season grasses was investigated. Some selected organic and inorganic amendments (i.e., humic acid, ferrous sulphate, and silicon) were applied as foliar sprays five times during the winter season from late October to March. This was repeated over two years in field trials involving salt-affected soils. The physiological and chemical parameters of the plants, including plant height; fresh and dry weight per plot; total chlorophyll content; and nitrogen, phosphorus, iron, and potassium content, were measured. The results showed that all the studied amendments improved the growth of seashore paspalum and Tifway bermudagrass during this period compared to the control, with a greater improvement observed when using ferrous sulphate and humic acid compared to silicon. For seashore paspalum, the highest chlorophyll content in April was recorded after the application of ferrous sulphate at a level of 1000 ppm. The current research indicates that when grown on salt-affected soils, these amendments can be used in warm-season grasses to maintain turf quality during cold periods of the year. Further research is needed to examine any negative long-term effects of these amendments and to explain their mechanisms.