Functional Analysis Of The Wheat Stearoyl-ACP Desaturase Gene TaSSI2-1

The SSI2 encoded stearoyl-acyl carrier protein-desaturase(SACPD), which could catalyze conversion of stearic acid(18:0) to oleic acid(18:1). The ssi2 mutants enhanced resistance to bacteria, oomycete pathogens and Cucumber mosaic virus. In this study, we cloned four TaSSI2 genes from wheat cultivar Sumai 3. For functional characterization, we demonstrated its expression pattern in response to hormones and subcellular localization. Furthermore, BSMV-VIGS and the transgenic Brachypodium were used to analyze its function involved in powdery mildew and FHB. The main results are as follows:1. TaSSI2-1 、 TaSSI2-2 、 TaSSI2-3 and TaSSI2-4 were cloned from wheat and their sequences were analysed. The open reading frame of TaSSI2-1 and TaSSI2-2 encoded 392 amino acids protein, shared over 98% of sequence identity. The open reading frame of TaSSI2-3 encoded 391 amino acids protein, and TaSSI2-4 encoded 333 amino acids protein. TaSSI2-3 and TaSSI2-4 shared over 99% of sequence identity, and phylogenetic analysis showed that they were involved in the OsSSI2 protein groups.2. Subcellular location with tobacco and onion epidermis cells showed that TaSSI2-1 was possibly located on golgi apparatus secreted vesicles.3. The real-time quantitative reverse transcription PCR was used to analyze expression profiles of TaSSI2-1. The results showed that TaSSI2-1 can be significantly reduced by methyl jasmonate, with expression of 5% at 24 h contrast to 0h. Interestingly, salicylic acid had a less pronounced effect in its expression.4. After silencing TaSSI2-1 by BSMV-VIGS approach, Huixianhong enhanced resistance to powdery mildew. The detached leaf assays showed that down-regulating of TaSSI2-1 enhanced susceptibility to the hemi-biotrophic Fusarium graminearum, which was consistent with the wheat spikes results. The data indicated that TaSSI2-1 played different role in the resistance to powdery mildew and Fusrium head blight.5. The involvement of TaSSI2-1 in plant defence against FHB was further addressed by investigating Brachypodium plants transformed with the cauliflower mosaic virus 35 S promoter-driven TaSSI2-1 for resistance to infection by F. graminearum.6. To expand VIGS utility, we successfully silenced TaPDS in Aegilops tauschii AL8/78 and Triticum.dicoccoides AS14. After 12 days of virus infection, the photo-bleaching phenotype was observed in new emerging leaves of BSMV:TaPDS. Thus, BSMV-VIGS can be used in Aegilops tauschii and Triticum.dicoccoides for functional analyse.