The protist ubiquitin ligase effector PbE3-2 targets RD21A to impede plant immunity
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Abstract
Clubroot caused by the soil-borne protist pathogen Plasmodiophora brassicae is one of the most devastating diseases of Brassica oil and vegetable crops worldwide. Understanding the pathogen infection strategy is crucial for the development of disease control. However, the molecular mechanism by which this pathogen promotes infection remains largely unknown. Here, we identified a P. brassicae -secreted effector PbE3-2 that impedes plant immunity by ubiquitinating the immune regulator RD21A for degradation. Overexpression of PbE3-2 in Arabidopsis thaliana resulted in higher susceptibility to P. brassicae and decreases in chitin-triggered reactive oxygen species burst and expression of marker genes in salicylic acid signaling. PbE3-2 interacted with and ubiquitinated RD21A in vitro and in vivo . Mutant plants deficient in RD21A exhibited similar susceptibility and compromsied immune responses as in PbE3-2 overexpression plants. These results suggest that P. brassicae promotes clubroot disease through RD21A degradation mediated by the effector PbE3-2. As PbE3-2 is widely conserved across different P. brassicae pathotypes, the degradation of RD21A by PbE3-2 might be a prevalent infection strategy in this pathogen.
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Working model of the mechanism for PbE3 to regulate plant immunity.
This is a very thorough study that uses clever techniques to describe the function of a protein from a Rhizarian species that doesn't have developed genetic tools. The data tells a convincing story and supports the claims made in this paper. Thank you for sharing this work as an open access preprint
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esides, rd21a was more susceptible to B. cinerea than Col-0 (Fig. 6D)
Was S. sclerotiorum also tested like in the PbE3-2 overexpression plants?
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PbE3-2 interacts with the plant cysteine protease RD21A
Figure 4 provides very convincing evidence that pbE3-2 interacts with RD21A in vivo. A minor point would be Fig4E could be improved by displaying the mCherry signal in magenta rather than red for color blind readers who can't distinguish the yellow-green differences in the merge. But very convincing figure!
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Data were normalized to ACTIN2 expression in RT-qPCR analys
Do you know that PbE3-2 expression isn't impacting actin expression? If you normalized to 3 random "house-keeping" genes would the data look the same? The data makes sense and fits nicely with the other experiments but actin is highly involved in plant immunity so might not be the best control?
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BAX-induced cell death.
It could be helpful to define BAX at some point. It can be difficult for non-plant scientists (myself included) to understand what it means that PbE3-2 confers BAX resistance without having this information readily available.
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