Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2016
Publication Date: 5/5/2016
Citation: Burbank, L.P., Stenger, D.C. 2016. A temperature-independent cold-shock protein homolog acts as a virulence factor in Xylella fastidiosa. Molecular Plant-Microbe Interactions. 29:335-344.
Interpretive Summary: Pierce’s disease (PD) of grapevine remains a significant problem for grape growers in California. This disease is restricted to warmer climates due to limited survival of the pathogen, Xylella fastidiosa (Xf), at low temperatures. Very little is known about why Xf is sensitive to cold and what factors affect the temperature dependence of PD. Many bacterial species rely on production of cold shock proteins (CSPs) for protection against temperature extremes and environmental stresses. This study characterizes the function of a previously undescribed CSP in Xf that is important for survival under cold and salt stress, and for full expression of disease symptoms in infected grapevines. Increased knowledge of factors impacting pathogen survival and ability to cause disease in the host is important for predicting disease incidence and severity, and for development of control strategies.
Technical Abstract: Xylella fastidiosa (Xf), causal agent of Pierce’s Disease (PD) of grapevine, is mainly prevalent in warmer climates. Subjecting Xf-infected grapevines to cold temperatures can, in many cases, effectively eliminate the bacterial population. However, little is known regarding physiological responses of Xf to cold temperatures. Cold shock proteins (CSPs), a family of nucleic acid binding proteins, act as chaperones facilitating translation at low temperatures. Bacterial genomes often encode multiple CSPs that are strongly induced following exposure to cold. Additionally, CSPs contribute to the general stress response through mRNA stabilization and post-transcriptional regulation. A putative CSP homolog (Csp1) with RNA binding activity was identified in Xf strain Stag’s Leap. The csp1 gene lacked the long 5’ untranslated region characteristic of cold-inducible genes, and was expressed in a temperature-independent manner. As compared with the wild type, a deletion mutant of csp1 ('csp1) had decreased survival rates following cold exposure and salt stress in vitro. The deletion mutant also was significantly less virulent in grapevine as compared with the wild type, even in the absence of cold stress. These results suggest an important and broader function, beyond cold tolerance, for Csp1 during colonization of plants by Xf.