A Regulatory Network of Heat Shock Modules-Photosynthesis-Redox Systems in Response to Cold Stress Across a Latitudinal Gradient in Bermudagrass

Heat-shock transcription factor HsfA8a regulates heat stress response in Sorbus pohuashanensis

MAIN CONCLUSION

The SpHsfA8a upregulated expression can induce the expression of multiple heat-tolerance genes, and increase the tolerance of Arabidopsis thaliana to high-temperature stress. Sorbus pohuashanensis is an ornamental tree used in courtyards. However, given its poor thermotolerance, the leaves experience sunburn owing to high temperatures in summer, severely affecting its ornamental value. Heat-shock transcription factors play a critical regulatory role in the plant response to heat stress. To explore the heat-tolerance-related genes of S. pohuashanensis to increase the tree's high-temperature tolerance, the SpHsfA8a gene was cloned from S. pohuashanensis, and its structure and expression patterns in different tissues and under abiotic stress were analyzed, as well as its function in heat tolerance, was determined via overexpression in Arabidopsis thaliana. The results showed that SpHsfA8a encodes 416 amino acids with a predicted molecular weight of 47.18 kDa and an isoelectric point of 4.63. SpHsfA8a is a hydrophilic protein without a signal peptide and multiple phosphorylation sites. It also contains a typical DNA-binding domain and is similar to MdHsfA8a in Malus domestica and PbHsfA8 in Pyrus bretschneideri. In S. pohuashanensis, SpHsfA8a is highly expressed in the roots and fruits and is strongly induced under high-temperature stress in leaves. The heterologous expression of SpHsfA8a in A. thaliana resulted in a considerably stronger growth status than that of the wild type after 6 h of treatment at 45 °C. Its proline content, catalase and peroxidase activities also significantly increased, indicating that the SpHsfA8a gene increased the tolerance of A. thaliana to high-temperature stress. SpHsfA8a could induce the expression of multiple heat-tolerance genes in A. thaliana, indicating that SpHsfA8a could strengthen the tolerance of A. thaliana to high-temperature stress through a complex regulatory network. The results of this study lay the foundation for further elucidation of the regulatory mechanism of SpHsfA8a in response of S. pohuashanensis to high-temperature stress.

Comparative Physiological and Transcriptome Analyses of Tolerant and Susceptible Cultivars Reveal the Molecular Mechanism of Cold Tolerance in Anthurium andraeanum

Anthurium andraeanum is a tropical ornamental flower. The cost of Anthurium production is higher under low temperature (non-freezing) conditions; therefore, it is important to increase its cold tolerance. However, the molecular mechanisms underlying the response of Anthurium to cold stress remain elusive. In this study, comparative physiological and transcriptome sequencing analyses of two cultivars with contrasting cold tolerances were conducted to evaluate the cold stress response at the flowering stage. The activities of superoxide dismutase and peroxidase and the contents of proline, soluble sugar, and malondialdehyde increased under cold stress in the leaves of the cold tolerant cultivar Elegang (E) and cold susceptible cultivar Menghuang (MH), while the soluble protein content decreased in MH and increased in E. Using RNA sequencing, 24,695 differentially expressed genes (DEGs) were identified from comparisons between cultivars under the same conditions or between the treatment and control groups of a single cultivar, 9132 of which were common cold-responsive DEGs. Heat-shock proteins and pectinesterases were upregulated in E and downregulated in MH, indicating that these proteins are essential for Anthurium cold tolerance. Furthermore, four modules related to cold treatment were obtained by weighted gene co-expression network analysis. The expression of the top 20 hub genes in these modules was induced by cold stress in E or MH, suggesting they might be crucial contributors to cold tolerance. DEGs were significantly enriched in plant hormone signal transduction pathways, trehalose metabolism, and ribosomal proteins, suggesting these processes play important roles in Anthurium's cold stress response. This study provides a basis for elucidating the mechanism of cold tolerance in A. andraeanum and potential targets for molecular breeding.

Differential Regulations of Antioxidant Metabolism and Cold-Responsive Genes in Three Bermudagrass Genotypes under Chilling and Freezing Stress

As a typical warm-season grass, bermudagrass growth and turf quality begin to decrease when the environmental temperature drops below 20 °C. The current study investigated the differential responses of three bermudagrass genotypes to chilling stress (8/4 °C) for 15 days and then freezing stress (2/-2 °C) for 2 days. The three genotypes exhibited significant variation in chilling and freezing tolerance, and Chuannong-3, common bermudagrass 001, and Tifdwarf were ranked as cold-tolerant, -intermediate, and -sensitive genotypes based on evaluations of chlorophyll content, the photochemical efficiency of photosystem II, oxidative damage, and cell membrane stability, respectively. Chuannong-3 achieved better tolerance through enhancing the antioxidant defense system to stabilize cell membrane and reactive oxygen species homeostasis after being subjected to chilling and freezing stresses. Chuannong-3 also downregulated the ethylene signaling pathway by improving CdCTR1 expression and suppressing the transcript levels of CdEIN3-1 and CdEIN3-2; however, it upregulated the hydrogen sulfide signaling pathway via an increase in CdISCS expression under cold stress. In addition, the molecular basis of cold tolerance could be associated with the mediation of key genes in the heat shock pathway (CdHSFA-2b, CdHSBP-1, CdHSP22, and CdHSP40) and the CdOSMOTIN in Chuannong-3 because the accumulation of stress-defensive proteins, including heat shock proteins and osmotin, plays a positive role in osmoprotection, osmotic adjustment, or the repair of denatured proteins as molecular chaperones under cold stress. The current findings give an insight into the physiological and molecular mechanisms of cold tolerance in the new cultivar Chuannong-3, which provides valuable information for turfgrass breeders and practitioners.

Genome-wide transcriptional profiling provides clues to molecular mechanisms underlying cold tolerance in chickpea

Chickpea is an important food legume cultivated in several countries. A sudden drop in autumn temperature, freezing winter temperature, and late spring cold events result in significant losses in chickpea production. The current study used RNA sequencing of two cold tolerant (Saral) and sensitive (ILC533) Kabuli chickpea genotypes to identify cold tolerance-associated genes/pathways. A total of 200.85 million raw reads were acquired from the leaf samples by Illumina sequencing, and around 86% of the clean reads (199 million) were mapped to the chickpea reference genome. The results indicated that 3710 (1980 up- and 1730 down-regulated) and 3473 (1972 up- and 1501 down-regulated) genes were expressed differentially under cold stress in the tolerant and sensitive genotypes, respectively. According to the GO enrichment analysis of uniquely down-regulated genes under cold stress in ILC533, photosynthetic membrane, photosystem II, chloroplast part, and photosystem processes were enriched, revealing that the photosynthesis is severely sensitive to cold stress in this sensitive genotype. Many remarkable transcription factors (CaDREB1E, CaMYB4, CaNAC47, CaTCP4, and CaWRKY33), signaling/regulatory genes (CaCDPK4, CaPP2C6, CaMKK2, and CaHSFA3), and protective genes (CaCOR47, CaLEA3, and CaGST) were identified among the cold-responsive genes of the tolerant genotype. These findings would help improve cold tolerance across chickpea genotypes by molecular breeding or genetic engineering.

Genome-wide identification of heat shock transcription factor families in perennial ryegrass highlights the role of LpHSFC2b in heat stress response

Perennial ryegrass (Lolium perenne) is a cool-season turf and forage grass. Heat shock transcription factors (HSFs) play an important role in regulating plant abiotic stress. However, HSFs in perennial ryegrass have rarely been characterized. Here, 25 LpHSFs were identified from the perennial ryegrass genome. Phylogenetic analysis showed that the LpHSFs could be classified into 12 subclasses. Gene structure analysis showed that 22 LpHSFs have only one intron. Cis-acting elements analysis revealed that the promoter of 15 LpHSFs contained hormone-responsive and abiotic stress-responsive elements. Expression profile analysis indicated that 24 LpHSFs were differentially expressed under submerge, drought, heat, and cold stresses. In addition, a subclass C2 gene, LpHSFC2b, was significantly induced by abiotic stresses. The LpHSFC2b protein is localized to the nucleus, and heterologous expression of LpHSFC2b in Arabidopsis improves plant thermotolerance. This study provides insights useful for the breeding of stress tolerance in perennial ryegrass.

A Novel Beta-Glucosidase Gene for Plant Type Was Identified by Genome-Wide Association Study and Gene Co-Expression Analysis in Widespread Bermudagrass

Bermudagrass (Cynodon spp.) is one of the most widely distributed warm-season grasses globally. The growth habits and plant type of bermudagrass are strongly associated with the applied purpose of the landscape, livestock, and eco-remediation. Therefore, persistent efforts are made to investigate the genetic basis of plant type and growth habits of bermudagrass. Here, we dissect the genetic diversity of 91 wild bermudagrass resources by genome-wide association studies (GWAS) combined with weighted gene co-expression analysis (WGCNA). This work is based on the RNA-seq data and the genome of African bermudagrass (Cynodon transvaalensis Burtt Davy). Sixteen reliable single-nucleotide polymorphisms (SNPs) in transcribed regions were identified to be associated with the plant height and IAA content in diverse bermudagrass by GWAS. The integration of the results from WGCNA indicates that beta-glucosidase 31 (CdBGLU31) is a candidate gene underlying a G/A SNP signal. Furthermore, both qRT-PCR and correlation coefficient analyses indicate that CdBGLU31 might play a comprehensive role in plant height and IAA biosynthesis and signal. In addition, we observe lower plant height in Arabidopsis bglu11 mutants (homologs of CdBGLU31). It uncovers the breeding selection history of different plant types from diverse bermudagrass and provides new insights into the molecular function of CdBGLU31 both in plant types and in IAA biosynthetic pathways.