One of the most efficient plant resistance reactions to pathogen attack is the hypersensitive response, a form of programmed cell death at infection sites. The Arabidopsis transcription factor MYB30 is a positive regulator of hypersensitive cell death responses. Here we show that MIEL1 (MYB30-Interacting E3 Ligase1), an Arabidopsis RING-type E3 ubiquitin ligase that interacts with and ubiquitinates MYB30, leads to MYB30 proteasomal degradation and downregulation of its transcriptional activity. In non-infected plants, MIEL1 attenuates cell death and defence through degradation of MYB30. Following bacterial inoculation, repression of MIEL1 expression removes this negative regulation allowing sufficient MYB30 accumulation in the inoculated zone to trigger the hypersensitive response and restrict pathogen growth. Our work underlines the important role played by ubiquitination to control the hypersensitive response and highlights the sophisticated fine-tuning of plant responses to pathogen attack. Overall, this work emphasizes the importance of protein modification by ubiquitination during the regulation of transcriptional responses to stress in eukaryotic cells.

No abstract

Plant and animal pathogens inject type III effectors (T3Es) into host cells to suppress host immunity and promote successful infection. XopD, a T3E from Xanthomonas campestris pv vesicatoria, has been proposed to promote bacterial growth by targeting plant transcription factors and/or regulators. Here, we show that XopD from the B100 strain of X. campestris pv campestris is able to target MYB30, a transcription factor that positively regulates Arabidopsis thaliana defense and associated cell death responses to bacteria through transcriptional activation of genes related to very-long-chain fatty acid (VLCFA) metabolism. XopD specifically interacts with MYB30, resulting in inhibition of the transcriptional activation of MYB30 VLCFA-related target genes and suppression of Arabidopsis defense. The helix-loop-helix domain of XopD is necessary and sufficient to mediate these effects. These results illustrate an original strategy developed by Xanthomonas to subvert plant defense and promote development of disease.

We hereby confirm that the original images are those first published in PNAS. When preparing the figures for submission to PNAS, the raw images were cropped and/or stretched to match the other blots and saved in the format for submission. Unfortunately, we did not systematically archive an independent copy of each raw image, and only the final version of the figures was stored. Fig. 3 appears to have areas of unmarked splicing and background inconsistencies, but we are confident, however, in the scientific accuracy of the data despite being unable to provide the original images."Further, we acknowledge that images of yeast colonies in Fig. S1B are indeed duplicated. Our intention was to represent the presence (or absence) of yeast growth observed with the different protein combinations. We recognize that this should have been clearly indicated in the figure legend and apologize for this omission. We have been able to retrieve the original results and prepared the revised figure below showing growth of yeast colonies expressing the different protein combinations. We apologize for any inconvenience the publication of these figures may have caused." The corrected Fig. S1 and its corrected legend appear below. The SI has been corrected online.