| Plant immune system comprises three main layers. Recognition of conserved microbe-associated molecular patterns (MAMPs) initiates the first layer of immune response, MAMP-triggered immunity (MTI). However successful pathogens utilize virulent strategies, such as effector proteins, to suppress MTI and facilitate their growth, resulting into effector-triggered susceptibility (ETS). In response to ETS, plants acquire resistance proteins to monitor the presence of the effector proteins, leading to stronger immune response, effector-triggered immunity (ETI). During the plant immune response, large-scale transcriptional reprogramming is activated by numerous transcription (co)factors. The Arabidopsis TGA factors have been shown to be required for resistance to disease. In the present study, the biological functions of clade I TGA factors (TGA1 and TGA4) during plant immune responses were investigated in depth.;My results demonstrate that TGA1 and TGA4 are positive regulators in disease resistance against virulent pathogens, such as bacterial pathogen Pseudomonas syringae and fungal pathogen Colletotrichum higginsianum. In addition, TGA1 and TGA4 positively contribute to disease resistance against a nonpathogenic strain, P. syringae pv. tomato hrcC-, an avirulent strain, P.s.t. AvrRpt2 and a nonhost pathogen, P. syringae pv. phaseolicola 1448a.;Loss of resistance in the tga1-1 tga4-1 double mutant was shown to be associated with defects in cell wall-based defence responses, including callose deposition, apoplastic oxidative burst and extracellular PATHOGENESIS-RELATED 1 (PR-1) protein accumulation. Interestingly, transcript levels of PR-1, callose synthase and other genes encoding defence proteins accumulated at, or above, wild-type levels in the mutants. Furthermore, the double mutant is more sensitive to the glycosilation inhibitor, tunicamycin, indicative of a compromised endoplasmic reticulum (ER) stress response. These results suggest that clade I TGA factors control defence-related secretion events that are required for cell wall-associated defence responses.;Analysis of the non-expressor of pathogenesis-related genes 1 (npr1-1) mutant and an tga1-1 tga4-1 npr1-1 triple mutant indicate that clade I TGA factors act substantially independent of NPR1 during plant immune responses. Moreover, mutation of clade I TGA factors also results in developmental changes, including curly leaves and late flowering. Together, these results demonstrate that clade I TGA factors play a unique role in mediating both defence responses and developmental processes. |
