Date Published: September 26, 2013
Publisher: Public Library of Science
Author(s): Jiping Xuan, Yufeng Song, Hongxiao Zhang, Jianxiu Liu, Zhongren Guo, Yuelou Hua, Joshua L Heazlewood.
Zoysiagrass, the most cold-tolerant grass among the warm-season turfgrasses, is often used as a model species for isolating cellular components related to cold stress. To understand the proteomic responses to cold stress in zoysiagrass stolons, we extracted stolon proteins from Zoysiajaponica, cv. Meyer (cold-tolerant) and Z. metrella, cv. Diamond (cold-sensitive), which were grown with or without cold treatment. Approximately 700 proteins were resolved on 2-DE gels, and 70 protein spots were differentially accumulated. We further observed that 45 of the identified proteins participate in 10 metabolic pathways and cellular processes. A significantly greater number of proteins accumulated in the Meyer than in the Diamond and 15 increased proteins were detected only in the Meyer cultivar under cold stress. Furthermore, we propose a cold stress-responsive protein network composed of several different functional components that exhibits a balance between reactive oxygen species (ROS) production and scavenging, accelerated protein biosynthesis and proteolysis, reduced protein folding, enhanced photosynthesis, abundant energy supply and enhanced biosynthesis of carbohydrates and nucleotides. Generally, the cold-tolerant Meyer cultivar showed a greater ROS scavenging ability, more abundant energy supply and increased photosynthesis and protein synthesis than did the cold-sensitive Diamond cultivar, which may partly explain why Meyer is more cold tolerant.
Low temperature is one of the most serious types of environmental stress and can reduce growth and cause rolling and withering of plant leaves. It is particularly important for plant biologists to understand the molecular mechanisms underlying the plant response to low temperature . Plants usually present several strategies, including gene regulation, to defend against cold stress. Many studies have focused on gene expression profiles during cold stress, because cold-responsive proteins are likely to be involved in cold tolerance . Several approaches, including the identification of novel responsive genes, determination of their expression patterns, and understanding their functions in stress responses, have been applied to develop effective engineering strategies that may lead to greater stress tolerance . Recently, with the advent of proteomics, gene expression during cold stress and acclimation has been studied via both transcriptomic and proteomic strategies. Microarray analyses have also shown that cold alters the expression of myriad genes [3,4], whereas proteomic approaches have identified no more than 150 proteins related to cold tolerance in Arabidopsis and rice [5,6,7,8].
Many plants become more resistant to freezing temperatures when first exposed to low nonfreezing temperatures, a process known as cold acclimation or cold hardening . The degree of freeze tolerance of Arabidopsis thaliana increased after a 4°C treatment . In this study, the freeze tolerance under cold stress of Meyer and Diamond were analyzed using electrolyte leakage (EL) method, under cold treatment, the freeze tolerance of both Meyer and Diamond increased. To further study the molecule mechanism for the increasing of freeze tolerance in zoysiagrass stolons under cold stress, a proteomic approach was used. In this study, comparative analysis of the proteins accumulating in freezing-tolerant and freezing–sensitive species led to the identification of many differentially accumulated proteins. Some of these proteins have been well characterized regarding their response to cold and other stresses, but others have not been well studied with respect to their role in plant stress response.
In conclusion, the abundances of many protein spots related to photosynthesis, energy metabolism, protein biosynthesis and proteolysis were increased or induced under long-term cold stress, to a greater extent in freeze-tolerant Meyer than in freeze-sensitive Diamond. Antioxidant defense proteins associated with ROS scavenging, such as APX, CAT and Tr-h, were increased under cold stress in Meyer, suggesting that these proteins may contribute to cold tolerance in this zoysiagrass. Our results suggest that the superior freeze tolerance observed in Zoysia. spp. Willd. plants could mainly be associated with the maintenance of proteins that are involved in photosynthesis (Rubisco large subunit), protein biosynthesis and proteolysis (IF, EF-Tu and proteasome α3 subunit), energy metabolism (NADH-plastoquinone oxidoreductase subunit 1, ATPase α subunit, ATPase β subunit, ENO and ADKs) and antioxidant defense (APX, CAT and Tr-h). Further analyses will be conducted to confirm the accumulation patterns of these cold-responsive proteins via western blotting and to investigate the enzyme activities of certain proteins that exhibit differential expression between cold-tolerant and cold-sensitive genotypes. Such information will provide further insights into the biological functions of these proteins related to cold tolerance.