Smut fungi as a stratagem to characterize rust effectors: opportunities and challenges
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(2020) 36:150
REVIEW
Smut fungi as a stratagem to characterize rust effectors: opportunities and challenges Rajdeep Jaswal1 · Sivasubramanian Rajarammohan1 · Himanshu Dubey2 · T. R. Sharma1,3 Received: 8 May 2020 / Accepted: 5 September 2020 © Springer Nature B.V. 2020
Abstract The rust pathogens are one of the most complex fungi in the Basidiomycetes. The development of genomic resources for rust and other plant pathogens has opened the opportunities for functional genomics of fungal genes. Despite significant progress in the field of fungal genomics, functional characterization of the genome components has lacked, especially for the rust pathogens. Their obligate nature and lack of standard stable transformation protocol are the primary reasons for rusts to be one of the least explored genera despite its significance. In the recently sequenced rust genomes, a vast catalogue of predicted effectors and pathogenicity genes have been reported. However, most of these candidate genes remained unexplored due to the lack of suitable characterization methods. The heterologous expression of putative effectors in Nicotiana benthamiana and Arabidopsis thaliana has proved to be a rapid screening method for identifying the role of these effectors in virulence. However, no fungal system has been used for the functional validation of these candidate genes. The smuts, from the evolutionary point of view, are closely related to the rust pathogens. Moreover, they have been widely studied and hence could be a suitable model system for expressing rust fungal genes heterologously. The genetic manipulation methods for smuts are also well standardized. Complementation assays can be used for functional validation of the homologous genes present in rust and smut fungal pathogens, while the species-specific proteins can be expressed in the mutant strains of smut pathogens having reduced or no virulence for virulence analysis. We propose that smuts, especially Ustilago maydis, may prove to be a good model system to characterize rust effector proteins in the absence of methods to manipulate the rust genomes directly. Keywords Functional genomics · Gene characterization · Plant pathogens · Rust fungi · Smut fungi
Introduction The rust pathogens encompass a large class of fungi infecting diverse plant species ranging from forest plants/trees to agriculturally important crops (Lorrain et al. 2019). There are 168 rust genera that comprise of approximately 7000 species, and more than half of them belong to the genus Puccinia (McKenzie 1998). These pathogens follow a dual
* T. R. Sharma [email protected] 1
National Agri-Food Biotechnology Institute (NABI), Sector‑81 (Knowledge City), PO Manauli, S.A.S. Nagar, Mohali, Punjab 140306, India
2
ICAR-National Institute for Plant Biotechnology, Pusa Campus, New Delhi 110012, India
3
Present Address: Crop Science Division, Indian Council of Agricultural Research, New Delhi 110001, India
life cycle producing five different types of spores in two taxonomically unrelated hosts. The
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