Effects Of Phytochrome Downstream Transcription Factor Gene Silencing On The Growth, Nutritional Quality And Stress Tolerance To Pst DC3000 In Tomato

Tomato (Solanun lycopersicum) is one of the most important vegetables worldwide. Because of its richness in vitamins and nutrients, it’s popular with the majority of consumers. Tomato is not only one of the largest vegetables cultivated in greenhouse, but also an important representative species of Solanaceae family. Nutrients in plants are controlled by genetic factors as well as environmental factors. Plants can sense the surrounding environment of light intensity, light quality, light to light cycle and to respond to the changes, forming the light receptor system. Many studies have shown that the light signaling genes in this system can affect the nutritional quality of tomato, but also brought some problems like plant dwarfing, reducing resistance and other issues. Therefore, it has practical significance to study the role of light signaling genes in nutritional quality and resistance as well as its mechanism. In this study, tomato (Solanum lycopersicum Mill.) was used as plant material to better understand the importance of light signaling genes in plant growth, photosynthetic characteristics and the regulation of nutritional quality by using virus induced gene silencing (VIGS) approach. We also investigated the involvement of light signaling genes in regulating biotic stress tolerance to Pst DC3000. The key findings are as follows:1.We constructed four vectors by VIGS for the phytochrorne downstream transcription factors:pTRV-DET1, pTRV-DDBl, pTRV-COP1 and pTRV-CSN5. Silencing of those genes inhibited the growth in tomato plants. Moreover, the photosynthetic characteristics were also affected. Photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of DET1 and CSN5 gene-silenced plants were remarkably declined.In addition, the leaf chlorophyll content was changed in gene-silenced plants; however, the carotenoid content was significantly increased.2. We also studied the effects of different phytochrome downstream transcription factor gene silencing on nutritional quality and antioxidant capacity in tomato. The results showed that silencing phytochrome downstream transcription factor could improve the nutritional quality and antioxidant capacity of tomato to some extent, as indicated by increased soluble sugar, flavonoids, total phenol, anthocyanin content and antioxidant capacity, etc. Particularly, flavonoids, total phenol and anthocyanin content were greatly increased in DETl, DDB1 and CSN5 gene-silenced plants.3. Finally, we studied the response of phytochrome downstream transcription factor gene silenceing against Pst DC3000 infection in tomato plant. The leaf phenotype, colony growth, PAL activity, chlorophyll fluorescence, SA content and disease resistance gene expression levels and other indicators were tested to analyze the phytochrome downstream transcription factor-mediated resistance mechanism against Pst DC3000 infection. The results showed that silencing tomato phytochrome downstream transcription factor reduces tomato plants’resistance to Pst DC3000. Among all silenced plants, DET1 and DDB1 gene-silenced plants showed the lowest resistance. The main mechanism is that TRV plants had an early H2O2 burst, and it might serve as secondary messenger to induce ICS gene expression. ICS is responsible for the biosynthesis of SA, which can further trigger disease resistance in plants. Unlike TRV plants, DET1 gene-silenced plants did not show an early H2O2 burst and the content of H2O2 in DDB1 gene-silenced plants was remarkably higher, which might cause stress to the plant and thus reducing the resistance to Pst DC3000 infection.