Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2011
Publication Date: 6/23/2011
Citation: Klosterman, S.J., Anchieta, A.G., Garcia-Pedrajas, M.D., Maruthachalam, K., Hayes, R.J., Subbarao, K.V. 2011. SSH reveals a linkage between a senescence-associated protease and Verticillium wilt symptom development in lettuce (Lactuca sativa). Physiological and Molecular Plant Pathology. 76:48-58. Interpretive Summary: The soilborne fungus Verticilllium dahliae causes the disease Verticillium wilt on lettuce and other crops. The development of sources of lettuce with resistance to Verticillium wilt offers the best long term alternative for pathogen control. The identification of molecular markers for resistance or susceptibility by the analyses of gene expression in response to the fungus may be useful to speed the development of resistance in lettuce. In this study, we have identified and examined genes that are differentially expressed in diseased lettuce leaves in response to the fungus and in healthy leaves from plants that were not inoculated with the fungus. Most prominently, genes displaying similarity with other plant defense genes were identified in the diseased plant tissue but not in healthy tissue. Interestingly, one of these genes expressed in diseased leaves but not healthy green leaves may be linked with initiating leaf symptoms that are observed in the susceptible plants infected with the fungus. This gene encodes a protein that shares high similarity with plant proteins that are involved in protein degradation and that are only expressed in senescent plant leaves. As in other plants, the leaf symptoms associated with Verticillium wilt sometimes can resemble senescence. Thus, we speculate that further analyses of this gene may provide insight into the genetic basis of symptom development in lettuce.
Technical Abstract: Suppression subtractive hybridization (SSH) was employed to identify lettuce (Lactuca sativa) genes that are differentially expressed in symptomatic leaves infected with Verticillium dahliae. Genes expressed only in symptomatic leaves included those with homology to pathogenesis-related (PR) protein genes PR-3, PR-5, and a putative cysteine protease (LsCP2). Quantitative real-time reverse transcription PCR (RT-qPCR) revealed that LsCP2 was expressed in senescent leaves, but at significantly higher levels in symptomatic leaves. LsCP2 shares homology with plant cysteine proteases that are expressed in senescing leaves and may therefore accelerate or contribute to the leaf symptoms observed in a lettuce-V. dahliae interaction.