Os03g0315400

Its gene name OsMYB2, is a R2R3-type MYB gene, expression a MYB-type transcription factor plays a important role in the tolerance to abiotic stress of plants.

Annotated Information

Function

1、Overexpression of OsMYB2 enhanced tolerance to salt cold, and dehydration stress（figure 1）.

The involvement of OsMYB2 in salt, cold, and osmotic stress was investigated by exposing wild-type and the transgenic plants grown in hydroponic solution with NaCl, low temperature, and PEG. There was no difference between transgenic and wild-type plants when grown under normal, non-stressed conditions in hydroponic solution (A). Phenotypically, most OsMYB2-overexpressing seedlings remained green and showed continuous growth, whereas both wild-type and RNAi seedlings showed severe leaf rolling and wilting after exposure to the salt, cold, and osmotic stress (B-D).In addition, the two transgenic rice lines overexpressing OsMYB2 grown in soil also exhibited greater tolerance to NaCl, cold, and drought stress than wild-type and RNAi plants（data not shown）

WT:wildtype; OE2 and OE3: OsMYB2 overexpression strain; Ri1 and Ri3: OsMYB2 RNAi strain;

2、Overexpression of OsMYB2 altered sensitivity of seed germination and growth to salt stress and ABA(figure 2).

This study also determined the survival rate for wild-type and transgenic plants grown in both hydroponic solution and soil challenged with salt, cold, and osmotic stress.the survival rate of overexpressing lines was significantly higher than that of wild-type and RNAi seedlings when exposed to salt stress (200 mM NaCl for 2 d), cold stress (5 ℃ for 3 d), and osmotic stress (20% PEG6000 for 2 d). The survival rates of the two overexpressing lines higher than those of wild-type and RNAi plants were also observed when rice seedlings grown in soil were challenged by salt, cold, and drought stress（D-F）

3、OsMYB2-overexpression plants accumulated greater amount of proline and soluble sugars(figure 3).

Exposure of both wild-type and transgenic seeds to NaCl reduced their germination rate (A). However, germination of OsMYB2-overexpressing seeds was less inhibited by NaCl than that of wild-type and RNAi seeds. For example, seed germination rate of the two OsMYB2-overexpressing lines (OE2, OE3) was 81% and 86% when incubated in the presence of 100 mM NaCl, while germination rate for wildtype and RNAi (Ri1, Ri3) seeds was found to be 51%, 49%, and 53% under the identical conditions, respectively. The effect of NaCl on seedling growth was also examined. In the saline medium containing 150 mM NaCl, the OsMYB2- overexpressing plants exhibited faster growth and their shoots were significantly longer than wild-type plants (Fig. 6B, C). In contrast to salt stress, seed germination of OsMYB2- overexpressing lines was more sensitive to ABA than that of wild-type and RNAi lines, such that wild-type and RNAi lines had higher seed germination rate than Fig. 3. Molecular characterization and phenotypes of OsMYB2 transgenic rice. (A) OsMYB2 expression in wild-type and transgenic rice. Total RNAs from 14-d-old wild-type and transgenic rice plants were isolated, reverse-transcribed, and analysed by realtime reverse-transcription PCR. Actin was used as an internal control. Error bars are based on three replicates. (B) The phenotypes of the T3 generation of wild-type and transgenic plants after growing on 1/2 MS medium for 14 days. (C) The phenotypes of the T3 generation of wild-type and transgenic plants after growing in soil for 30 days. Data are mean6SE of three biological replicates. Asterisks indicate statistically significant differences (P < 0.05) between wild-type (WT) and transgenic lines (OE and Ri). 2546 | Yang et al. Downloaded from http://jxb.oxfordjournals.org/ at Institute of Biophysics,CAS on May 28, 2014 OsMYB2-overexpressing lines when ABA was present in the incubation medium (D). Like seed germination, growth of OsMYB2-overexpressing seedlings was more inhibited by ABA than that of wild-type and RNAi seedlings, as shown by a shorter length of OsMYB2-overexpressing seedlings than wild-type and RNAi seedlings when grown in the presence of ABA (E, F). No difference in shoot length of wild-type and the transgenic plants grown in control medium was found.

4、OsMYB2-overexpression plants accumulated less H2O2 and MDA under salt stress(figure 4).

The effects of NaCl on H2O2 and MDA contents in wild-type and transgenic rice were investigated and no significant differences in H2O2 and MDA contents were found in the absence of NaCl in the incubation medium (A, B). There were marked increases in H2O2 and MDA contents in both wildtype and transgenic plants upon exposure to 200 mM NaCl. However, the salt stress-induced increases in H2O2 and MDA contents were less in the OsMYB2-overexpressing plants than those in the wild-type and RNAi plants. These results indicate that overexpression of OsMYB2 confers greater tolerance of the oxidative stress associated with salt stress. The lower content of H2O2 in the OsMYB2-overexpressing plants under salt stress prompted this study to test whether the difference in H2O2 accumulation between wild-type and the OsMYB2-overexpressing lines resulted from differences in the activities of the major antioxidant enzymes. Under normal conditions, activities of POD, SOD, and CAT were comparable among wild-type, OsMYB2-overexpressing, and RNAi plants (C-E). There were marked increases in activities of these enzymes for the rice seedlings upon exposure to salt stress. However, the salt stress-induced increases in activities of POD, SOD, and CAT were higher in the OsMYB2-overexpressing plants than the wild-type and RNAi plants (C-E). In contrast to OsMYB2- overexpressing plants, activities of these enzymes in the OsMYB2-RNAi lines did not differ from the wild-type plants under salt-stressed conditions (C-E). These results imply that overexpression of OsMYB2 confers a more efficient antioxidant system to counteract oxidative stress under saline conditions.

5、OsMYB2-overexpression plants affect some genes' expression profiles. Some genes upregulation can contribute to enhanced tolerance of plants to salt stress and some may involved in stress response.

Expression

OsMYB2 was detected in roots,shoots,leaves, and flowers, but it was specifically located in the nucleus(figure 5)

a、b、c: localization of GFP ; e、d、f:localization of GFP-OsMYB2

The response of OsMYB2 expression to salt, cold, and dehydration stress was monitored by real-time RT-PCR. An increase in the OsMYB2 transcript was observed after 30 min of exposure to salt stress. The salt stress-induced increase in the OsMYB2 transcript peaked after 5 h of salt stress, and thereafter the transcript declined gradually under salt stress . A similar increase in the OsMYB2 transcript was also observed when rice seedlings were exposed to low temperature (2℃) or osmotic stress (20% PEG) . In addition, treatment of rice seedlings with ABA also led to an increase in expression of OsMYB2. In contrast, exogenous application of salicylic acid reduced the expression of OsMYB2, while no effect of indoleacetic acid and brassinosteroids on the OsMYB2 transcript was observed. OsMYB2 was detected in roots, shoots, leaves, and flowers under non-stressed conditions, with the expression being greatest in leaves, followed by roots and shoots . The strong induction of this gene by abiotic stress prompted this study to check its promoter sequence (1500 bp upstream from the transcription start site) by searching the promoter sequence against the PLACE database [(http://www.dna.affrc.go.jp/PLACE/)]. The promoter of OsMYB2 contains stress-responsive related cis-elements, such as ABRE and MYB and MYC recognition sites

Evolution

Phylogenetic tree of MYB proteins(figure 6).

OsMYB2 representative by LOC_Os3g20090 is belong to C12, and of which are involved in stress response.

Labs working on this gene

1 State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, PR China

2 Graduate University of the Chinese Academy of Sciences, Beijing 100049, PR China

References

A R2R3-type MYB gene, OsMYB2, is involved in salt, cold, and dehydration tolerance in rice.An Yang1,2, Xiaoyan Dai1 and Wen-Hao Zhang*,1.Journal of Experimental Botany, Vol. 63, No. 7, pp. 2541–2556, 2012.