|De los reyes, B|
Submitted to: Proceedings International Rice Genetic Symposium
Publication Type: Abstract only
Publication Acceptance Date: 10/2/2006
Publication Date: 11/9/2006
Citation: De Los Reyes, B.G., Cheng, C., Yun, K.Y., Jia, Y., Ressom, H., Yun, S.J. 2006. Candidate regulators of the cold stress response gene regulon of rice. Proceedings 4th International Rice Genetic Symposium, Montpellier, France. p.117. Interpretive Summary:
Technical Abstract: Transcriptional regulatory network is an important component of the mechanisms that define the adaptive responses of plants to cold stress. In cold-acclimating plants, the centerpiece of such network is the CBF/DREB family of AP2-type transcription factors. In non-acclimating plants like rice, the nature of such network is not very well understood. This study took advantage of the significant differences in cold-sensitivity between indica and japonica rice and the available genomics resources for rice to dissect the hierarchical organization of the cold stress response gene regulon of plants that do not cold-acclimate. To address this goal, the early cold-stress response transcriptome of the cold-tolerant japonica rice (CT6748-8-CA-17) was profiled by interrogation of a cDNA microarray consisting of >5,000 potential abiotic stress-associated genes with a pair of control (28oC) and stressed (10oC) RNA isolated after 0.5, 2, 6, 12 and 24 hours. Gene expression data showed that the early response involves two waves of induction. The first started within the first 2 hours of stress, i.e., ‘rapidly induced early response genes’ (Group-I). The second did not start until after 2 hours of stress, i.e., ‘delayed induced early response genes’ (Group-II). Potential regulators of the cold stress genetic network were also deduced by hierarchical clustering. Group-I includes a novel bZIP protein with similarity to the tungro virus resistance-associated RF2a and RF2b. Group-II includes a bHLH protein similar to ICE1, a Myb protein similar to OsMyb4, and a C3HC4 zinc-finger protein related to HOS1. Analysis of the promoters of representative functional genes that are co-regulated under Group-II showed high frequency of potential bZIP-target cis-elements, supporting the functional significance of the rapidly induced bZIP protein gene. Analysis of temporal patterns by quantitative PCR revealed genotype-specific expression signatures, in which all four transcription factors had significant differences in both the timing of induction and relative transcript abundance between cold-intolerant and tolerant genotypes. In the intolerant genotype (INIAP12), the transcription factors were downregulated by cold stress until 12 hours when expression began to increase slightly. In contrast, the transcription factors were rapidly upregulated by cold stress within the first 0.5 hours and then reached high and more sustained levels within the next 2 to 6 hours in the tolerant genotype (CT6748-8-CA-17). Overall, the intolerant genotype exhibited about 6 hours delay in the expression of the candidate regulators with respect to the tolerant genotype. These results support the rationale that timely and robust expression of major regulatory genes plays a critical role in cold tolerance mechanisms. The layered expression of these transcription factors suggests a mechanism for fine-tuned regulation of the cold stress response genetic network.