Location: Molecular Plant Pathology LaboratoryTitle: Sugar beet polygalacturonase-inhibiting proteins with 11 LRRs confer Rhizoctonia, Fusarium and Botrytis resistance in Nicotiana plants
Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2018
Publication Date: 3/15/2018
Citation: Li, H., Smigocki, A.C. 2018. Sugar beet polygalacturonase-inhibiting proteins with 11 LRRs confer Rhizoctonia, Fusarium and Botrytis resistance in Nicotiana plants. Physiological and Molecular Plant Pathology. 102:200-208. http://doi.org.10.1016/j.pmpp.2018.03.001.
Interpretive Summary: Rhizoctonia solani, Fusarium solani and Botrytis cinerea are three pathogenic fungi that cause diseases in sugar beet, tobacco and many other commercially important crops, fruits and vegetables. During plant attack, fungi release a variety of degradative enzymes, such as endopolygalacturonase (PG), to break down plant cell walls. For self-protection, plants produce antimicrobial compounds such as polygalacturonase-inhibiting proteins (PGIPs) to inhibit fungal PGs. PGIPs contain a stretch of repeating amino acids (LRRs) that are responsible for the disease resistance response. Sugar beet PGIPs have longer LRR regions that are unique to sugar beet. To test the function of sugar beet PGIPs in fungal resistance, we introduced sugar beet PGIP genes into tobacco plants. We observed that sugar beet PGIP proteins protected tobacco plants from all three fungi. The level and specificity of protection was associated with small variations in the LRR region in the sugar beet PGIPs, indicating the importance of LRR in recognition of a specific fungal pathogen. We conclude that the longer LRR regions in the sugar beet PGIPs may provide for broader protection from fungal pathogens than other PGIPs with shorter LRRs. Scientists and breeders will use this information to develop improved crops with disease resistance that will increase yields, reduce usage of harmful pesticide and provide safer produce for the consumer.
Technical Abstract: Polygalacturonase-inhibiting proteins (PGIPs) are leucine-rich repeat (LRR) proteins that inhibit polygalacturonase (PG) enzymes secreted by pathogens to break down plant cell walls during early stage of disease development. Sugar beet (Beta vulgaris L.) PGIP genes (BvPGIPs) have 11 LRR domains as compared to 10 LRRs generally found in other plant species. To determine whether the BvPGIPs have a function in plant defense, BvPGIP1 and BvPGIP2 that differ in eight amino acids were fused with the CaMV 35S constitutive promoter and introduced into Nicotiana benthamiana. Crude PGIP protein extracts from BvPGIP1 transgenic plants significantly inhibited Rhizoctonia solani, Fusarium solani and Botrytis cinerea PGs. BvPGIP2 extract also inhibited PGs from F. solani and B. cinerea but did not inhibit PGs from R. solani. When transgenic BvPGIP plants were bioassayed for resistance, similar results were obtained. We propose that the eight amino acid difference between BvPGIP1 and BvPGIP2 contributed to the R. solani response and suggest that this approach can be used for defining novel PGIP activity against specific microbial PGs. This is a first report that documents the function of 11 LRR-containing PGIPs in resistance mechanisms.