Roles Of The TTG2Protein In Growth And Defense In Tobacco

In the process of growth and development, a lot of genes were activated in auxin signaling pathway in plants. When plants were infected by pathogens, some of these genes regulate auxin and SA signaling crosstalk to coordinate development and resistance. Our study showed that NtTTG2is one of the genes that regulate development and resistance of plants meanwhile.1. Roles of the TTG2protein in growth process and defense in tobaccoNtTTG2(Nicotiana tabacum Transparent TESTA GLABRA2) participates in the foundation of the trichome growth of tobacco. We successfully cloned this gene from tobacco NC89. The full length cDNA sequence of NtTTG2is1379bp. The result of Real-time PCR showed that the gene NtTTG2is expressed in all of the roots, stems, leaves, flowers and fruits, especially in the flowers. In the five steps of flowers’ development, the higher expression was detected in the late (S4and S5). We’ve successfully got TTG2-silencing (RNAi) NC89plant (TTG2iNC4) and TTG2-Overexpression Transgenic NC89plant (TOTNC1). We got the conclusion that NtTTG2play a role in the development of tobacco by observing the growth and taking notes the height of TCNC, TTG2iNC4and TOTNC1. ARF8, an auxin response factor, was NtTTG2-regulated as its expression was enhanced in TOTNC1and repressed in TTG2iNC4compared to TCNC. We inoculated tobacco mosaic virus (TMV) and Pcc to leaves of TTG2iNC4, TOTNC1and TCNC. The symptoms were more severe in TOTNC1and less severe in TTG2iNC4compared to TCNC, which suggested that NtTTG2repressed resistance of tobacco.2. NtTTG2modulates nuclear localization of ARF8and NPR1NtTTG2is characteristic of a typical WD40-domain protein that promote interaction with other proteins. However, NtTTG2didn’t interact with ARF8in live plants cells. A yellow-fluorescent protein (YFP) was fused to ARF8for transient expression assays. We use laser confocal microscopy to visualize fluorescent proteins of plant roots. Nuclear localization of ARF8-YFP was visualized in TOTNC1but the protein was little in TTG2iNC4nuclei. These results suggested that NtTTG2could promote nuclear localization of ARF8. Concurrent NtTTG2and NPR1gene silencing or NtTTG2silencing in the absence of SA accumulation compensated for the compromised defence as a result of the NPR1single-gene silencing or due to the absence of SA(Baoyan Li,2012). To our surprise, NtTTG2did not interact with NPRl but was able to modulate the subcellular localisation of the NPR1protein. When the production of NtTTG2was nullified, NPRl was found predominantly in the nucleus. On the contrary, when NtTTG2accumulated in transgenic plants, a large proportion of NPR1was retained in the cytoplasm. These results suggested that NtTTG2could sequester NPRl from nuclear localization.