Location: Cereal Disease LabTitle: Powdery mildew effectors AVRA1 and BEC1016 target the ER J-domain protein HvERdj3B required for immunity in barley
|LI, ZIZHANG - University Of Copenhagen|
|VELÁSQUEZ-ZAPATA, VALERIA - Iowa State University|
|Elmore, James - Mitch|
|LI, XUAN - University Of Copenhagen|
|XIE, WENJUN - University Of Copenhagen|
|BANERJEE, SAGNIK - Iowa State University|
|JØRGENSEN, HANS - University Of Copenhagen|
|PEDERSON, CARSTEN - University Of Copenhagen|
|THORDAL-CHRISTENSEN, HANS - University Of Copenhagen|
Submitted to: bioRxiv
Publication Type: Pre-print Publication
Publication Acceptance Date: 5/2/2022
Publication Date: N/A
Interpretive Summary: Powdery mildew fungi infect more than 9,500 agronomic and horticultural plant species. In order to prevent economic loss due to diseases caused by powdery mildew, plant breeders incorporate disease resistance genes into varieties that are grown for food, feed, fuel and fiber. One of these resistance genes provides instructions for assembly of the MLA immune receptor, an ancestral protein that provides disease resistance to powdery mildew, stem- and stripe rust in small grain cereal crops, such as barley, wheat, and rye. In these systems, corresponding host and pathogen proteins interact during fungal infection to initiate plant defense, often relying on basic cellular processes, such as the endoplasmic reticulum (ER) and protein quality control systems elsewhere in the cell. USDA, ARS, Iowa State University, and University of Copenhagen scientists used a combination of computer- and laboratory-based methods to identify and characterize a barley J-containing protein, HvERdj3B, as a host target for two diverse powdery mildew virulence proteins. Their analyses showed, for the first time, that HvERdj3B is an ER-localized protein, and that that upon infection, the fungal proteins and their barley target translocate from the plant cytosol into the ER lumen. These observations support the involvement of these proteins in promoting disease resistance.
Technical Abstract: Plant disease resistance often occurs upon direct or indirect recognition of pathogen effectors by host nucleotide-binding leucine-rich-repeat (NLR) receptors. The barley powdery mildew fungus, Blumeria graminis f. sp. hordei (Bgh), secretes hundreds of candidate secreted effector proteins (CSEPs) to facilitate pathogen infection and colonization. One of these, CSEP0008, is directly recognized by the barley NLR, MLA1, and therefore designated AVRA1. Here we show that AVRA1 and the sequence-unrelated Bgh effector BEC1016 (CSEP0491) suppress immunity in barley cells. We then used yeast 2-hybrid next-generation-interaction screens (Y2H-NGIS), followed by binary Y2H and bimolecular fluorescence complementation, to identify a common barley target of AVRA1 and BEC1016, the endoplasmic reticulum (ER)-localized J-domain protein, HvERdj3B. This is an ER protein quality control (ERQC) protein and silencing it increased the Bgh penetration rate in barley. HvERdj3B is localized to the ER lumen, and AVRA1 and BEC106 translocation into the ER was confirmed using a split GFP system. Together, these results suggest that the barley innate immunity, preventing Bgh entry into epidermal cells, is dependent on ERQC, which in turn is regulated by J-domain protein HvERdj3B and the two effectors. Previous work has shown that AVRA1 is directly recognized in the cytosol by the immune receptor, MLA1. We speculate whether the AVRA1 J-domain target being inside the ER, where it is inapproachable by NLRs, has forced the plant to evolve this challenging direct recognition.