Start Date: Mar 20, 2007
End Date: Mar 19, 2012
Objective 1 will use physiological assays previously developed in a cell suspension model system to 1) identify a limited number of plant bacterial interactions that display different physiological states of basal resistance or suppression and 2) characterize the corresponding changes in all detectable apoplastic phenolics and changes in redox status. The same bacterial isolates will also be used in whole plant experiments to 3) characterize the corresponding changes in apoplastic phenolics and redox status. Finally, we will 4) test whether addition of identified phenolics to suspension cells or whole plants interferes with basal resistance elicitation and suppression. Objective 2 will also involve multiple experimental approaches. A combination of Agroinfiltration and in situ hybridization techniques will be used to 1) identify the structural feature(s) of Eggplant latent viroid (ELVd) responsible for its ability to enter the chloroplast. A field study currently underway in Fort Pierce, FL will 2) test the ability of variants of citrus viroid III (CVd-III) to dwarf citrus growing under subtropical conditions. Finally, we will use a Saccharomyces cereviseae (baker’s yeast) experimental system to 3) study viroid transport from the cytoplasm to the nucleus and other fundamental features of viroid-host interaction. Objective 3 will examine the role of redox and viroid-induced RNA silencing in regulating host responses to infection. Using 454 DNA sequencing technology, we will compare small RNA profiles from four sets of tomato plants; i.e., uninfected control plants; plants infected with either a mild or severe strain of PSTVd; and transgenic plants that constitutively express a noninfectious hairpin RNA derived from PSTVd. Effects on host gene expression will be monitored by microarray analysis with special emphasis on down-regulated genes potentially involved in redox metabolism.