Membrane-Associated Ubiquitin Ligase (SAUL1) supresses temperature- and humidity-dependent autoimmunity in Arabidopsis

Disch, Eva-Maria; Tong, Meixuezi; Kotur, Tanja; Koch, Gerald GND; Wolf, Carl-Asmus; Li, Xin; Hoth, Stefan

Plants have evolved elaborate mechanisms to regulate pathogen defense. Imbalances in this regulation may result in autoimmune responses that are affecting plant growth and development. In Arabidopsis, SAUL1 encodes a plant U-box ubiquitin ligase and regulates senescence and cell death. Here, we show that saul1-1 plants exhibit characteristics of an autoimmune mutant. A decrease in relative humidity or temperature resulted in reduced growth and systemic lesioning of saul1-1 rosettes. These hysiological changes are associated with increased expression of salicylic acid–dependent and pathogenesis-related (PR) genes. Consistently, resistance of saul1-1 plants against Pseudomonas syringae pv. maculicola ES4326, P. syringae pv. tomato DC3000, or Hyaloperonospora arabidopsidis Noco2 was enhanced. Transmission electron microscopy revealed alterations in saul1-1 chloroplast ultrastructure and cell-wall depositions. Confocal analysis on aniline blue–stained leaf sections and cellular universal micro spectrophotometry further showed that these cell-wall depositions contain callose and lignin. To analyze signaling downstream of SAUL1, we performed epistasis analyses between saul1-1 and mutants in the EDS1/PAD4/SAG101 hub. All phenotypes observed in saul1-1 plants at low temperature were dependent on EDS1 and PAD4 but not SAG101. Taken together, SAUL1 negatively regulates immunity upstream of EDS1/PAD4, likely through the degradation of an unknown activator of the pathway.

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Disch, Eva-Maria / Tong, Meixuezi / Kotur, Tanja / et al: Membrane-Associated Ubiquitin Ligase (SAUL1) supresses temperature- and humidity-dependent autoimmunity in Arabidopsis. 2016.

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