Heat stress transcription factor A2s (HsfA2s) are key regulators in plant response to high temperature. Our objectives were to isolate an HsfA2 gene (CtHsfA2b) from a warm-season grass species, African bermudagrass (Cynodon transvaalensis Burtt-Davy) and to determine the physiological functions and transcriptional regulation of HsfA2 for improving heat tolerance. Gene expression analysis revealed that CtHsfA2b was heat-inducible and exhibited rapid response to increasing temperature. Ectopic expression of CtHsfA2b improved heat tolerance in Arabidopsis and restored heat-sensitive defects of Arabidopsis hsfa2 mutant, which was demonstrated by higher survival rate and photosynthetic parameters and lower electrolyte leakage in transgenic plants compared to the WT or hsfa2 mutant. CtHsfA2b transgenic plants showed elevated transcriptional regulation of several downstream genes, including those encoding ascorbate peroxidase (AtApx2) and heat shock proteins [AtHsp18.1-CI, AtHsp22.0-ER, AtHsp25.3-P and AtHsp26.5-P(r), AtHsp70b and AtHsp101-3]. CtHsfA2b was found to bind to the heat shock element (HSE) on the promoter of AtApx2 and enhanced transcriptional activity of AtApx2. These results suggested that CtHsfA2b could play positive roles in heat protection by up-regulating antioxidant defense and chaperoning mechanisms. CtHsfA2b has the potential to be used as a candidate gene to genetically modify cool-season species for improving heat tolerance.

Seashore paspalum (Paspalum vaginatum) is among the most salt- and cadmium-tolerant warm-season perennial grass species widely used as turf or forage. The objective of this study was to select stable reference genes for quantitative real-time polymerase chain reaction (qRT-PCR) analysis of seashore paspalum in response to four abiotic stresses. The stability of 12 potential reference genes was evaluated by four programs (geNorm, NormFinder, BestKeeper, and RefFinder). U2AF combined with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) showed stable expression in Cd-treated leaves and cold-treated roots. U2AF and FBOX were the most stable reference genes in Cd-treated roots and cold-treated leaves. In Polyethylene Glycol (PEG)- or salt-treated roots, the reference gene U2AF paired with either ACT or CYP were stable. SAND and CACS exhibited the most stability in salt-treated leaves, and combining UPL, PP2A, and EF1a was most suitable for PEG-treated leaves. The stability of U2AF and instability of UPL and TUB was validated by analyzing the expression levels of four target genes (MT2a, VP1, PIP1, and Cor413), and were shown to be capable of detecting subtle changes in expression levels of the target genes in seashore paspalum. This study demonstrated that FBOX, U2AF, and PP2A could be used in future molecular studies that aim to understand the mechanisms of abiotic stress tolerance in seashore paspalum.

Cadmium (Cd) is a non-essential heavy metal and high concentrations in plants causes toxicity of their edible parts and acts as a carcinogen to humans and animals. Paspalum vaginatum is widely cultivating as turfgrass due to its higher abiotic stress tolerance ability. However, there is no clear evidence to elucidate the mechanism for heavy metal tolerance, including Cd. In this study, an RNA sequencing technique was employed to investigate the key genes associated with Cd stress tolerance and accumulation in P. vaginatum. The results revealed that antioxidant enzyme activities catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and glutathione S-transferase GST) were significantly higher at 24 h than in other treatments. A total of 6820 (4457/2363, up-/down-regulated), 14,038 (9894/4144, up-/down-regulated) and 17,327 (7956/9371, up-/down-regulated) differentially expressed genes (DEGs) between the Cd1 vs. Cd0, Cd4 vs. Cd0, and Cd24 vs. Cd0, respectively, were identified. The GO analysis and the KEGG pathway enrichment analysis showed that DEGs participated in many significant pathways in response to Cd stress. The response to abiotic stimulus, the metal transport mechanism, glutathione metabolism, and the consistency of transcription factor activity were among the most enriched pathways. The validation of gene expression by qRT-PCR results showed that heavy metal transporters and signaling response genes were significantly enriched with increasing sampling intervals, presenting consistency to the transcriptome data. Furthermore, over-expression of PvSnRK2.7 can positively regulate Cd-tolerance in Arabidopsis. In conclusion, our results provided a novel molecular mechanism of the Cd stress tolerance of P. vaginatum and will lay the foundation for target breeding of Cd tolerance in turfgrass.

Seashore paspalum is a major warm-season turfgrass requiring frequent mowing. The use of dwarf cultivars with slow growth is a promising method to decrease mowing frequency. The present study was conducted to provide an in-depth understanding of the molecular mechanism of T51 dwarfing in the phenylpropane pathway and to screen the key genes related to dwarfing. For this purpose, we obtained transcriptomic information based on RNA-Seq and proteomic information based on iTRAQ for the dwarf mutant T51 of seashore paspalum. The combined results of transcriptomic and proteomic analysis were used to identify the differential expression pattern of genes at the translational and transcriptional levels. A total of 8311 DEGs were detected at the transcription level, of which 2540 were upregulated and 5771 were downregulated. Based on the transcripts, 2910 proteins were identified using iTRAQ, of which 392 (155 upregulated and 237 downregulated) were DEPs. The phenylpropane pathway was found to be significantly enriched at both the transcriptional and translational levels. Combined with the decrease in lignin content and the increase in flavonoid content in T51, we found that the dwarf phenotype of T51 is closely related to the abnormal synthesis of lignin and flavonoids in the phenylpropane pathway. CCR and HCT may be the key genes for T51 dwarf. This study provides the basis for further study on the dwarfing mechanism of seashore paspalum. The screening of key genes lays a foundation for further studies on the molecular mechanism of seashore paspalum dwarfing.

Drought stress is one of the crucial factors affecting plant growth and development in turfgrass species, especially during the summer season. Exogenous plant growth regulators are an effective and convenient approach to mitigating the adverse effects of drought stress on plant growth. The objectives of this study were to reveal the effects of exogenous carnosine or chitosan on turf performance and physiological indexes in bermudagrass (Cynodon transvaalensis × C. dactylon) in response to drought stress. Bermudagrass was foliar sprayed with carnosine or chitosan, and dose-dependent effects on turf quality were observed under drought stress. Under drought stress, foliar application of either carnosine (0.03%) or chitosan (10 mg L⁻¹) significantly increased turf quality, chlorophyll content, leaf relative water content, and decreased electrolyte leakage, malonaldehyde, and hydrogen peroxide content in comparison with untreated control in bermudagrass. Moreover, exogenous carnosine treatment significantly enhanced the activities of both catalase and peroxidase, but chitosan application only increased catalase activity. The results of this experiment were beneficial to the development of new plant growth regulators and would provide helpful insights for turf management under drought-stressed conditions.

Dollar spot is reported to be caused by multiple Clarireedia species and is a serious problem on many turfgrasses around the world. To our knowledge, the distribution of different Clarireedia species and their sensitivity profiles to fungicides remains unknown. In this study, a total of 275 isolates were characterized by ITS sequence. Amounts of 124, 59 and 75 isolates were identified as C. jacksonii, C. monteithiana and C. paspali, respectively, while each species of C. homoeocarpa and C. bennettii had only five isolates. Four and three isolates were identified as two potential new species, which remained to be further characterized. C. jacksonii and C. monteithiana were distributed worldwide, while C. paspali was restricted to China. Of the isolates with host information, 81% (93/115) and 19% (22/115) of C. jacksonii isolates were collected from C3 and C4 plants, respectively, 97% (56/58) of the C. monteithiana isolates were collected from C4 plants and all C. paspali isolates were collected from C4 plants. The coexistence of different Clarireedia species on the same C4 host type in the same locales was found in Shanghai (Paspalum vaginatum), Jiangsu (Paspalum vaginatum) and Florida (Cynodon dactylon). The study revealed that differential fungicide sensitivity patterns were observed in different species in Clarireedia for the first time. Similar differential sensitivity profiles were also found in the locales with coexistence of at least two species. The findings from this study suggest that the adjacent coexistence of different Clarireedia species and the differential fungicide sensitivity profiles of different species will complicate dollar spot disease control.