OsDREB genes in rice, Oryza sativa L., encode transcription activators that function in drought-, high-salt- and cold-responsive gene expression.
FunctionThe OsDREB proteins probably bind to the sequence and activate expression of these genes in rice. These rice genes are expected to be upregulated by overexpression of the OsDREB proteins.The structures of DREB1-type ERF/AP2 domains in monocots are closely related to each other as compared with that in the dicots. OsDREB1A is potentially useful for producing transgenic monocots that are tolerant to drought, high-salt, and/or cold stresses. OsDREB1A specifically binds DRE-related core binding motif, GCCGAC more preferentially than to ACCGAC unlike AtDREB1A, which shows efficient binding to both ACCGAC and GCCGAC. The responsiveness of OsDREB1A to NaCl and wounding stresses, in addition to its sensitivity to cold stress, imply that its role in the transduction of abiotic stress signals in rice is more similar to DREB1C rather than DREB1A in Arabidopsis. On the other hand, OsDREB1C was constitutively expressed in rice plants, which has a unique expression profile(Fig.1) .
Expression of OsDREB1A and OsDREB1B was induced by cold, whereas expression of OsDREB2A was induced by dehydration and high-salt stresses, and transgenic Arabidopsis that over-express OsDREB1A were tolerant to drought, high salt and cold stresses. Over-expression of transcription factor OsDREB1B could improve not only freezing tolerance but heat tolerance as well of Arabidopsis, which might lay a strong foundation for exploiting the freezing and heat tolerance of rice and other species. DREB/CBF genes have been induced in response to cold-, drought-, and high salt-stresses, but the expression of DREB1A and DREB1B genes have been observed only under cold stress.To investigate the response of rice DREB1s in abiotic stresses, we compared the expression of all these genes in rice variety IR64 under three types of stress (drought, salt, and cold) using microarray data from RiceGE (Fig. 2). .
Plants have evolved several mechanisms in order to cope with adverse environmental conditions. The transcription factors(TFs) belonging to the DREB1/CBF subfamily have been described as major regulators of the plant responses to different abiotic stresses. OsDREB1B is not only induced by low temperatures, but also by drought and mechanical stress.
Transcription levelThe gene expression of OsDREB1B (Os09g35010) was analysed in plants subjected to several abiotic stress conditions, using semi-quantitative reverse-transcription (RT) PCR. For this, 2-week-old rice seedlings were subjected to cold (5 and 10 ¬C), salt (200 mM NaCl), drought, and ABA (100 lM) treatments for up to 24 h (Fig. 3A and Supplementary Fig. S3). . In addition, it was observed that this regulation is temperature dependent and shows a similar pattern in both shoots and roots (Fig. 3A). When rice seedlings were subjected to 10 ¬C, the OsDREB1B transcript level was rapidly induced (10 min), reached a peak at 1–2 h, and then started to decrease, returning to basal levels afterwards. At 5 ¬C, however, the induction of OsDREB1B only started after 40 min of cold and remained high until the end of the assay. Rice seedlings treated with ABA or subjected to high salinity showed a similar gene expression pattern for OsDREB1B in both shoots and roots. The transcript level of OsDREB1B was rapidly (10 min) upregulated after the onset of stress and followed by a downregulation after 20–40 min. This pattern was also observed in shoots under drought stress, whereas in roots the transcript level of OsDREB1B was kept high at least during 24 h after drought treatment. This suggests that OsDREB1B may play an important role in the plant response to drought, particularly at root level. In the case of NaCl and ABA treatments, there was also a transient upregulation of OsDREB1B after 5–10 h of NaCl treatment in shoots and 1–2 h of ABA treatment in roots. However, given that these changes also appear in the mock control, they are likely to be not specific to NaCl and ABA treatments.
Under mock treatment, a circadian regulation of OsDREB1B could be observed, with the transcript level reaching a peak at 2–5 h after the start of the assay (6–9 h after dawn), decreasing afterwards. In addition, under the same treatment, OsDREB1B showed a transient increase of gene expression at 10 and 20 min. Since, in this case, the only change in conditions was the transfer of the plants to new growth medium, it was hypothesized if this upregulation could be due to a response to mechanical stress. Therefore, another assay was performed, in the same conditions as above, but where the plants were damaged and transferred to new medium. In this case, the OsDREB1B transcript level was highly induced in response to mechanical damage for at least 20 minutes, returning to basal levels afterwards (Fig. 3B). This may also explain the transient upregulation that was observed in the salt, drought, and ABA treatments around 10 and 20 min after the start of stress (Fig. 1A and Supplementary Fig. S1). Nevertheless, the transient induction observed in the salt and drought treatments seems to be more significant than the one seen in the mock treatment.
Labs working on this gene
- Japan International Research Center for Agricultural Sciences (JIRCAS)
- Ministry of Agriculture, Forestry and Fisheries, Japan
- RIKEN Tsukuba Institute
- the Youth Fund of Shanghai Academy of Agricultural Sciences
- the Shanghai Key Basic Research Project
- Council of Scientific and Industrial Research (CSIR)
- National Bureau of Plant Genetic Resources (NBPGR)
- Joseph G. Dubouzet, Yoh Sakuma, Yusuke Ito, et al. (2003) OsDREB genes in rice, Oryza sativa L., encode transcription activators that function in drought-, high-salt- and cold-responsive gene expression. The Plant Journal 33(4): 751-763.
- Qiu-lin Qin, Jin-ge Liu, Zhen Zhang, et al. (2007) Isolation, optimization, and functional analysis of the cDNA encoding transcription factor OsDREB1B in Oryza Sativa L. Molecular Breeding 19(4): 329-340.
- Ito Y, Katsura K, Maruyama K, et al. (2006) Functional analysis of rice DREB1/CBF-type transcription factors involved in cold-responsive gene expression in transgenic rice. Plant Cell Physiol 47:141–153.
- Donghai Mao;Caiyan Chen. (2012) Colinearity and Similar Expression Pattern of Rice DREB1s Reveal Their Functional Conservation in the Cold-Responsive Pathway. PLoS ONE 7(10): e47275
- Duarte D. Figueiredo;Pedro M. Barros;André M. Cordeiro, et al. (2012) Seven zinc-finger transcription factors are novel regulators of the stress responsive gene OsDREB1B. Journal of Experimental Botany 63(10): 3643-3656.