In an attempt to improve stress tolerance of tomato (Lycopersicon esculentum) plants, an expression vector containing an Arabidopsis C-repeat/dehydration responsive element binding factor 1 (CBF1) cDNA driven by a cauliflower mosaic virus 35S promoter was transferred into tomato plants. Transgenic expression of CBF1 was proved by northern-and western-blot analyses. The degree of chilling tolerance of transgenic T 1 and T 2 plants was found to be significantly greater than that of wild-type tomato plants as measured by survival rate, chlorophyll fluorescence value, and radical elongation. The transgenic tomato plants exhibited patterns of growth retardation; however, they resumed normal growth after GA 3 (gibberellic acid) treatment. More importantly, GA 3 -treated transgenic plants still exhibited a greater degree of chilling tolerance compared with wild-type plants. Subtractive hybridization was performed to isolate the responsive genes of heterologous Arabidopsis CBF1 in transgenic tomato plants. CATALASE1 (CAT1) was obtained and showed activation in transgenic tomato plants. The CAT1 gene and catalase activity were also highly induced in the transgenic tomato plants. The level of H 2 O 2 in the transgenic plants was lower than that in the wild-type plants under either normal or cold conditions. The transgenic plants also exhibited considerable tolerance against oxidative damage induced by methyl viologen. Results from the current study suggest that heterologous CBF1 expression in transgenic tomato plants may induce several oxidative-stress responsive genes to protect from chilling stress.Many tropical and subtropical crops, e.g. tomato (Lycopersicon esculentum), bell pepper (Capsicum annuum), and avocado (Persea americana), are sensitive to cold (Saltveit and Morris, 1990). Because of the susceptibility to chilling, the growing season of the crops is limited, and the quality of produce is affected. On the other hand, plants originating in the temperate zone are generally more tolerant to cold and have protective processes, such as cold acclimation (Thomashow, 1999). It has been demonstrated that the ability to cold acclimate is related to specific signal transduction pathways resulting in the activation of many cold-regulated (COR) genes (Thomashow, 1998).The COR genes, including RD29A (COR78), COR15a, KIN1, and COR6.6 of Arabidopsis, are inducible in response to cold treatment, ABA, and water-deficit stress (Thomashow, 1998). The C-repeat (CRT) and dehydration responsive element (DRE)-related motifs have been reported in the promoter sequences of these genes (Horvath et al., 1993;Nordin et al., 1993; Baker et al., 1994;Wang et al., 1995). The CRT/DRE binding factor 1 (CBF1) has been isolated using a yeast (Saccharomyces cerevisiae) onehybrid system (Stockinger et al., 1997). Overexpression of CBF1 can induce COR gene expression and result in increased tolerance to freezing temperature treatment without cold-acclimation (Jaglo-Ottosen et al., 1998). Arabidopsis CBF1 is also heterologously effective in canola ...

Rice (Oryza sativa) seedlings are particularly sensitive to chilling in early spring in temperate and subtropical zones and in high-elevation areas. Improvement of chilling tolerance in rice may significantly increase rice production. MYBS3 is a single DNA-binding repeat MYB transcription factor previously shown to mediate sugar signaling in rice. In this study, we observed that MYBS3 also plays a critical role in cold adaptation in rice. Gain-and loss-of-function analyses indicated that MYBS3 was sufficient and necessary for enhancing cold tolerance in rice. Transgenic rice constitutively overexpressing MYBS3 tolerated 4°C for at least 1 week and exhibited no yield penalty in normal field conditions. Transcription profiling of transgenic rice overexpressing or underexpressing MYBS3 led to the identification of many genes in the MYBS3-mediated cold signaling pathway. Several genes activated by MYBS3 as well as inducible by cold have previously been implicated in various abiotic stress responses and/or tolerance in rice and other plant species. Surprisingly, MYBS3 repressed the well-known DREB1/CBFdependent cold signaling pathway in rice, and the repression appears to act at the transcriptional level. DREB1 responded quickly and transiently while MYBS3 responded slowly to cold stress, which suggests that distinct pathways act sequentially and complementarily for adapting short-and long-term cold stress in rice. Our studies thus reveal a hitherto undiscovered novel pathway that controls cold adaptation in rice.

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