Author ORCID Identifier

http://orcid.org/0000-0003-4547-4675

Year of Publication

2016

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department

Plant Pathology

First Advisor

Dr. Aardra Kachroo

Abstract

Like humans, viral diseases also affect plants. Of these, viruses belonging to the potyvirus genus are the most prolific. The potyvirus soybean mosaic virus (SMV) is an important pathogen of the crop plant soybean. SMV causes mosaic symptoms (yellow areas alternate with dark green areas on the leaves of the plant) and can affect yield by reducing seed quality. Few cultivars from soybean can resist different SMV strains. To understand soybean defense mechanisms to SMV, I identified soybean proteins that interact with the helper component protease (HC-Pro) of SMV, which also functions as the suppressor of host RNA silencing and thereby contributes to viral virulence. A genome wide yeast two hybrid screen identified two HC-Pro interactors; BRI1-associated receptor kinase 1 (BAK1) and ubiquitin conjugating enzyme 2 (UBC2). Interactions with HC-Pro were confirmed using bimolecular florescence complementation (BiFC), and co-immunoprecipitations (Co-IP) assays. HC-Pro showed co-localization with both BAK1 and UBC2 in planta. Six isoforms of BAK1 were identified in soybean (BAK1 a, b, c, d, e, and f). Functional analysis showed that silencing the gene encoding BAK1a resulted in breakdown of resistance derived from the resistance (R) locus Rsv1, against SMV. Consistent with the fact that BAK1 is well known regulator of plant basal immunity, soybean plants silenced for BAK1 exhibited enhanced susceptibility to the bacterial pathogen Pseudomonas syringae. BAK1, a receptor-like kinase, functions as a co-receptor in plant defense signaling as well as brassinosteroid-derived signaling during plant growth. My data indicates that HC-Pro is phosphorylated in the presence of BAK1 and this requires the T341 residue which regulates virus avirulence in Rsv1 plants. This is an important finding because although BAK1 is well known to phosphorylate BRI1 and other defense-related receptors, its involvement in phosphorylating pathogen-derived proteins has not been reported. My work raises the possibility that BAK1-derived phosphorylation of HC-Pro may be important to trigger Rsv1-mediated resistance against SMV.

Digital Object Identifier (DOI)

https://doi.org/10.13023/ETD.2016.455

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