Zoysiagrasses (Zoysia spp.) are warm‐season turfgrasses primarily grown in the southern and transition zones of the United States. An understanding of the physiological and proteomic changes that zoysiagrasses undergo during cold acclimation may shed light on phenotypic traits and proteins useful in selection of freeze‐tolerant genotypes. We investigated the relationship between cold acclimation, protein expression, and freeze tolerance in cold acclimated (CA) and nonacclimated (NA) plants of Zoysia japonica Steud. cultivars Meyer (freeze‐tolerant) and Victoria (freeze‐susceptible). Meristematic tissues from the grass crowns were harvested for proteomic analysis. Freeze testing indicated that cold acclimation accounted for a 1.9‐fold increase in plant survival than nonacclimation treatment. Overall, proteomic analysis identified 62 protein spots differentially accumulated in abundance under cold acclimation. Nine and 22 unique protein spots were identified for Meyer and Victoria, respectively, with increased abundance or decreased abundance. In addition, 23 shared protein spots were found among the two cultivars in response to cold acclimation. Function classification revealed that these proteins were involved primarily in transcription, signal transduction and stress defense, carbohydrate and energy metabolism, and protein and amino acid metabolism. Several proteins of interest for their association with cold acclimation were identified. Further investigation of these proteins and their functional categories may contribute to increase our understanding of the differences in freezing tolerance among zoysiagrass germplasm.
Zoysiagrasses (Zoysia spp.) are relatively low‐input and warm‐season turfgrasses which have grown in popularity in the United States since their introduction in the 1890s. Over 30 improved zoysiagrass cultivars were released in the past three decades, but many lack freezing tolerance and their use is limited to warm‐humid climates. Understanding the genetic controls of winter hardiness and freezing tolerance in zoysiagrass could considerably benefit the breeding efforts to increase tolerance to freezing stress. In the present study, controlled environment acclimation and freezing tests were used to evaluate a Meyer × Victoria zoysiagrass mapping population for post‐freezing surviving green tissue (SGT) and regrowth (RG). Quantitative trait loci (QTL) mapping analysis identified nine QTL associated with SGT, eight QTL linked to RG, and 22 QTL common in both traits, accounting for between 6.4 and 12.2% of the phenotypic variation. Eleven regions of interest overlapped with putative winter injury QTL identified in a previous field study. Upon sequence analysis, homologs of several abiotic response genes were found underlying these overlapping QTL regions. The homologs of these gene encode transcription factors, cell wall modification‐related proteins, and defense signal transduction‐related proteins. After further validation, these QTL and their associated markers have potential to be used in future breeding efforts for the development of a broader pool of zoysiagrass cultivars capable of surviving in cold climates.
Zoysiagrasses (Zoysiaspp.) are warm season turfgrasses primarily grown in the southern and transition zones of the United States. An understanding of the physiological changes that zoysiagrasses undergo during cold acclimation may shed light on physiological phenotypic traits useful in selection of freeze tolerant genotypes. We investigated the relationship between cold acclimation, protein expression, and freeze tolerance in cold-acclimated (CA) and non-acclimated (NCA) plants ofZoysia japonicaSteud. cultivars ‘Meyer’ (freeze-tolerant) and ‘Victoria’ (freeze-susceptible). Freeze tolerance was assessed using chambers reaching −6, −8, −10, and −12°C. Additionally, meristematic tissues from the grass crowns of ‘Meyer’ and ‘Victoria’ were harvested for proteomic analysis after a four week cold acclimation period. Freeze testing indicated that cold acclimation accounted for a 1.9-fold increase in plant survival compared to the non-acclimation treatment. Overall, proteomic analysis identified 62 protein spots having at least a twofold change in abundance under cold acclimation. Nine and 22 unique protein spots were identified for Meyer and Victoria, respectively, with increased abundance (up-regulated) or decreased abundance (down-regulated). In addition, 23 shared protein spots were found among the two cultivars having differential expression in response to cold acclimation. In Meyer, protein response to cold acclimation was primarily upregulated, while in Victoria, protein response was primarily downregulated. These cold acclimation responsive proteins were found to be involved primarily in transcription, metabolism, protein destination and storage, and energy production. As identified through MALDI-TOF/TOF mass spectrometry followed matching of protein homologues against the NCBI Arabidopsis database, major proteins of interest for their association with cold acclimation were LEA 3, MAPK, SOD, GAST1, Phytochrome A, ATP synthase, AGP, PLD, and PSII. Further investigation of these proteins and their functional categories may contribute to increase our understanding of the differences in freezing tolerance among zoysiagrass germplasm.
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