Translating ribosome affinity purification profiling of plum pox virus (PPV) infected leaf tissues in Prunus domestica L reveals post-dormancy spatial coordination of defense responses in phloem tissues

Authors: Collum, Tamara - Tami; Stone, Andrew; Sherman, Diana; Rogers, Elizabeth; Dardick, Christopher - Chris; CULVER, JAMES - University Of Maryland

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2019
Publication Date: 10/23/2019
Citation: Collum, T.D., Stone, A.L., Sherman, D.J., Rogers, E.E., Dardick, C.D., Culver, J.N. 2019. Translating ribosome affinity purification profiling of plum pox virus (PPV) infected leaf tissues in Prunus domestica L reveals post-dormancy spatial coordination of defense responses in phloem tissues. Molecular Plant-Microbe Interactions. 33(1) 66-77. https://doi.org/10.1094/MPMI-06-19-0152-FI.
DOI: https://doi.org/10.1094/MPMI-06-19-0152-FI

Interpretive Summary: Plum pox virus (PPV) is one of the most economically important pathogens of stone fruits infecting a wide range of species including plum, peach, apricot, cherry, almond, as well as, ornamental Prunus. PPV infection can lead to reduced fruit quality, premature fruit drop and a shortened productive lifespan of the tree. Viruses that infect fruit trees move through the plant’s phloem, which is part of the vascular tissue, from the roots to newly emerging leaves each spring. The ability of the virus to move throughout the plant is a key step in the establishment of disease and requires specific viral and plant interactions. Unfortunately, there is little information about these viral and plant interactions at the cellular and molecular levels specifically in plant phloem vascular tissues. This is in part due to the technical difficulty of physically separating phloem from surrounding tissues. In this study, we used a newer tissue specific sampling method called translating ribosome affinity purification (TRAP) to identify plant responses to PPV infection in plum (Prunus domestica L.) at four developmental stages. We found the phloem tissue is highly responsive to PPV infection compared to other tissue types. Phloem specific alterations included genes associated with defense and stress responses. The results reveal new insights into the dynamics of host defense responses in specific tissue types during virus infection. Identified genes also provide new candidates for manipulating the timing of plant defense responses to disrupt the normal virus lifecycle and develop new strategies for disease resistance.

Technical Abstract: Plum pox virus (PPV) is the causative agent of Sharka, a devastating disease of stone fruits. Within its perennial host, PPV infection levels and associated disease can vary greatly depending upon tissue type and developmental age. However, little is known about the host responses that occur in key tissues such as the phloem, which is the location of systemic virus spread. Here, we demonstrate translating ribosome affinity purification (TRAP) is an effective tool to identify phloem and non-phloem specific gene responses to PPV infection during leaf development in plum (Prunus domestica L.). Results indicated that during secondary leaf morphogenesis (four- and six-week-old leaves) the phloem has a disproportionate response to PPV infection with two- to six-fold more differentially expressed genes (DEGs) in phloem than non-phloem tissues despite similar infection levels. In contrast, in mature twelve-week-old leaves virus infection levels drop significantly in phloem tissues but not in non-phloem tissues. This drop in phloem virus infection correlates with a 18-fold drop in phloem specific DEGs. Furthermore, genes associated with defense responses including RNA silencing are spatially coordinated in response to PPV accumulation and are induced in phloem tissues at four to six weeks. Combined these findings highlight the temporal and spatial dynamics of leaf tissue responses to virus infection and reveal the importance of phloem responses within a perennial host.