Functional Analysis Of Rice OsSAE1 In Salt Response

AP2/ERF superfamily proteins are plant-specific transcription factors that contain a large number of members. It has been demonstrated that the AP2/ERF proteins play an imperative role in the transcriptional of diverse biological processes, such as plant growth and development, and response to environmental cues. Among AP2/ERF superfamily, the AP2 family memebers contain two AP2/ERF domains, which mainly involved in plant development. In addition, some members of the AP2 faminly factors contain a conserved EAR(ERF-associated amphiphilic repression) motif in their C-terminal region, which has been reported function as a repression domain.Os SAE1(SALT AND ABA RESPONSE ERF1, LOC_Os06g43220) encodes an AP2 family protein in rice, with an “Lx Lx L” type EAR motif in the C-terminal region. Sequence alignment and phylogenetic analysis showed that there are homologous proteins of Os SAE1 in a variety of plants. The expression of Os SAE1 could be induced by Na Cl, drought, ABA, and ACC treatment. It is found that Os SAE1 expressed in root, stem, leaf, leaf sheaths, spikelet and seed, but mainly in leaf. Trans-activating ability tests in yeast demonstrated that Os SAE1 could act as a transactivator and its C-terminal of the protein is necessary for its activity. The function of Os SAE1 was investigated through RNA interference transgenic rice. The panicle length and filled grain number per panicle reduced, while the effective tillering increased in RNAi lines compared to that in WT. In addition, seed germination of RNAi lines was delayed, compared with that of WT, and the difference was enhanced by salt stress. And the RNAi lines were more sensitive to salt stress during early seedling growth stage as compared with WT. Correspondly, the determination of chlorophyll, MDA content confirmed the above observations. Our results showed that chlorophyll content of RNAi lines was lower, while MDA content was higher than that of WT under salt stress, demonstrating that Os SAE1 positively regulates rice salt stress response.It has been reported that ABA plays important roles in plant development and stress responses. We speculated that the delay of seed germination of Os SAE1 RNAi lines might be related to ABA. Firstly, our data showed that the Os SAE1 RNAi lines were more sensitive to ABA during seed germination and seedling development stage compared with wild type and leaf water loss rate of RNAi lines was lower than that of WT. The detection of endogenous ABA contents showed that there was no significant difference between Os SAE1 RNAi lines and WT, indicating that the delay of seed germination and more-sensitivity to salt stress of RNAi lines are not related to ABA biosynthesis. We further detected the transcriptional levels of ABA signaling pathway genes. Our analysis revealed that the expression of Os ABI5 was significantly higher in RNAi lines than that in WT. Therefore, our results indicate that Os SAE1 is involved in rice salt response through regulation of ABA signaling pathway.