DSM1 is a typical Raf-like MAPKKK in rice.
DSM1 might be a novel MAPKKK functioning as an early signaling component in regulating responses to drought stress by regulating scavenging of ROS in rice.
- Two allelic dsm1 mutants were more sensitive than wildtype plants to drought stress at both seedling and panicle development stages. The dsm1 mutants lost water more rapidly than wild-type plants under drought stress, which was in agreement with the increased drought-sensitivity phenotype of the mutant plants.
- Sequence analysis indicated that the insertion site of the dsm1-1 mutant is located in exon 12, 7,174 bp downstream of ATG, and the T-DNA of the dsm1-2 mutant is inserted in intron 10, 6,734 bp downstream of ATG.
- Ning et al. checked the sensitivity of the dsm1-1 mutant to salt stress, and results showed that the mutant was more sensitive to salt stress than the wild type, but no significant difference was observed for cold stress.
- The dsm1 mutant is sensitive to oxidative stress, the enhanced sensitivity of the dsm1 mutant to oxidative stress resulted from reduced ability of ROS (at least H2O2) scavenging.
- Three independent RNAi lines:
- Among 24 T0 RNAi plants checked, five showed significantly decreased expression of DSM1. Three independent RNAi lines were selected for drought testing at the seedling stage.
- DSM1-RNAi lines were also hypersensitive to drought stress, which was in agreement with the phenotype of dsm1 mutant plants. The survival rate of DSM1-RNAi lines was only 10% to 15%, whereas 60% to 70% of wild-type plants recovered. Consistent with this result, detached leaves of DSM1-RNAi lines lost water more quickly than the wild-type leaves, which suggesting that DSM1 plays essential roles in drought resistance in rice.
- By real-time PCR analysis, the DSM1 gene was induced by salt, drought, and abscisic acid(ABA), but not induced by cold stress but rather slightly suppressed. Overexpression of DSM1 in rice increased the tolerance to dehydration stress at the seedling stage.
- Microarray analysis revealed that two peroxidase (POX) genes, POX22.3 and POX8.1, were sharply down-regulated compared to wild type, suggesting that DSM1 may be involved in reactive oxygen species (ROS) signaling. Peroxidase activity, electrolyte leakage, chlorophyll content, and 3,3'-diaminobenzidine staining revealed that the dsm1 mutant was more sensitive to oxidative stress due to an increase in ROS damage caused by the reduced POX activity.
To determine the subcellular localization of DSM1, the DSM1 cDNA was fused in frame to the GFP marker gene under the control of cauliflower mosaic virus 35S promoter. In the transgenic rice expressing DSM1-EGFP, the fluorescence was observed only in the nuclei. Green fluorescence produced by sGFP-DSM1 overlapped with blue fluorescence produced by CFP-GHD7, which further confirmed that DSM1 is a nuclear protein.
Thus, DSM1 is localized in the nucleus.
- Alignment of the full-length protein sequence of DSM1 with the well-characterized plant MAPKKKs suggests that DSM1 has high sequence similarity in both the KD and the RD to EDR1 ('73% identity in KD and 36% identity in RD) and CTR1 (65% identity in KD and 42% identity in RD). Both EDR1 and CTR1 belong to the B3 subgroup of plant Raf-like MAPKKKs.
- In contrast, DSM1 showed relatively low sequence identity with other plant MAPKKK proteins. For example, DSM1 shared only 31% and 30% identity, respectively, with AtMEKK1 and NPK1 even in the conserved KD. A phylogenetic tree based on the conserved KD and the position of the KD also placed DSM1 into the Raf-like MAPKKK family.
Labs working on this gene
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research(Wuhan), Huazhong Agricultural University, Wuhan 430070, China
- Donald Danforth Plant Science Center, St. Louis, Missouri 63132
- Ning J, Li X, Hicks L M, et al. A Raf-like MAPKKK gene DSM1 mediates drought resistance through reactive oxygen species scavenging in rice[J]. Plant physiology, 2010, 152(2): 876-890.
- Ichimura K, Shinozaki K, Tena G, et al. Mitogen-activated protein kinase cascades in plants: a new nomenclature[J]. Trends in plant science, 2002, 7(7): 301-308.