Abstract
Bermudagrass (Cynodon dactylon L pers.) is one of the most geographically adapted and utilized of the warm-season grasses. However, bermudagrass adaptation to the Northern USA is limited by freeze damage and winterkill. Our study provides the first large-scale analyses of gene expression in bermudagrass regenerative crown tissues during cold acclimation. We compared gene expression patterns in crown tissues from highly cold tolerant “MSU” and susceptible “Zebra” genotypes exposed to near-freezing temperatures. Suppressive subtractive hybridization was used to isolate putative cold responsive genes Approximately, 3845 transcript sequences enriched for cold acclimation were deposited in the GenBank. A total of 4589 ESTs (3184 unigenes) including 744 ESTs associated with the bermudagrass disease spring dead spot were printed on microarrays and hybridized with cold acclimated complementary Deoxyribonucleic acid (cDNA). A total of 587 differentially expressed unigenes were identified in this study. Of these only 97 (17%) showed significant NCBI matches. The overall expression pattern revealed 40% more down- than up-regulated genes, which was particularly enhanced in MSU compared to Zebra. Among the up-regulated genes 68% were uniquely expressed in MSU (36%) or Zebra (32%). Among the down-regulated genes 40% were unique to MSU, while only 15% to Zebra. Overall expression intensity was significantly higher in MSU than in Zebra (p value ≤ 0.001) and the overall number of genes expressed at 28 days was 2.7 fold greater than at 2 days. These changes in expression patterns reflect the strong genotypic and temporal response to cold temperatures. Additionally, differentially expressed genes from this study can be utilized for developing molecular markers in bermudagrass and other warm season grasses for enhancing cold hardiness.
Highlights
Bermudagrass, Cynodon dactylon L Pers., is one of the most important warm-season perennial turf and forage grasses in use today and is widely adapted across a range of climatic zones extending between 45° north to 45° south latitudes [1,2]
Warm season bermudagrass crown tissues exposed to cold temperatures were hypothesized to produce significant changes in gene expression in support of the low temperature survival and the cold acclimation process
polymerase chain reaction (PCR) based suppression subtractive libraries were constructed from cold acclimated and non-acclimated crown tissues of MSU and Zebra resulting in 3845 enriched expression sequence taqs (ESTs) all of which were deposited in GenBank (Accession numbers: DN989227.1 to DN985375.1)
Summary
Bermudagrass, Cynodon dactylon L Pers., is one of the most important warm-season perennial turf and forage grasses in use today and is widely adapted across a range of climatic zones extending between 45° north to 45° south latitudes [1,2]. Bermudagrass varieties exhibit a wide range of tolerance to cold temperatures with LT50 values (the temperature at which 50% of the plants survive) ranging from -4.8° to -11.5°C [3,4]. This range suggests opportunities for further improvement through breeding or genetic engineering approaches. Bermudagrass’s ability to adapt to more temperate climates depends on its ability to cold acclimate. Winter survival with subsequent spring emergence and regeneration depends on the cold survival of these remnant tissues. In the advanced stages of cold acclimation, crown tissues undergo what might be referred to as a metabolically-inactive quiescent state, possibly related to dormancy
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