Putative rust fungal effector proteins in infected bean and soybean leaves

Authors: Cooper, Bret; Campbell, Kimberly; Beard, Hunter; Garrett, Wesley; ISLAM, NAZRUL - University Of Maryland

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2016
Publication Date: 3/24/2016
Publication URL: http://handle.nal.usda.gov/10113/62562
Citation: Cooper, B., Campbell, K., Beard, H.S., Garrett, W.M., Islam, N. 2016. Putative rust fungal effector proteins in infected bean and soybean leaves.Phytopathology. doi: 10.1094/PHYTO-11-15-0310-R.

Interpretive Summary: Little is known about the proteins that two fungi use to cause rust diseases on beans and soybeans. Knowledge of these proteins may lead to the discovery of chemicals that could prevent the infection of plants. Mass spectrometry was used to identify fungal proteins in infected beans and soybeans. We found 24 fungal proteins that appear to be specifically secreted by the one fungus on infected beans. We also found 16 proteins appear that appear to be specifically secreted by the other fungus in infected soybeans. There was overlap between the two sets which suggests that the fungi use similar proteins and mechanisms to cause disease. Several of these proteins appear to be involved in degrading the plant leaf cell wall. These data are most likely to influence scientists at universities, government agencies and companies who are designing new fungicides or methods to fight rust diseases.

Technical Abstract: The plant pathogenic fungi Uromyces appendiculatus and Phakopsora pachyrhizi cause debilitating rust diseases on common bean and soybean. These rust fungi secrete effector proteins that allow them to infect plants, but the effector repertoire for U. appendiculatus and P. pachyrhizi is not fully defined. The discovery of rust fungus effectors may eventually help guide decisions and actions that mitigate crop production loss. Therefore, we used mass spectrometry to identify thousands of proteins in infected beans and soybeans and in germinated fungal spores. The comparative analysis between the two helped differentiate a set of 24 U. appendiculatus proteins targeted for secretion that were specifically found in infected beans and a set of 34 U. appendiculatus proteins targeted for secretion that were found in germinated spores and infected beans. The proteins specific to infected beans included family 26 and family 76 glycoside hydrolases that may contribute to degrading plant cell walls. There were also several types of proteins with structural motifs that may aid in stabilizing the specialized fungal haustorium cell that interfaces the plant cell membrane during infection. There were 16 P. pachyrhizi proteins targeted for secretion that were found in infected soybeans, and many of these proteins resembled those from rust infected beans, which implies that these proteins are important to rust fungal pathology in general. This dataset provides insight to the biochemical mechanisms that rust fungi use to overcome plant immune systems and parasitize cells.