Molecular Mechanisms of Disease Resistance in Tomato
In tomato, resistance to bacterial speck disease is determined by the presence of resistance gene Pto in plants and the cognate aviurlence genes avrPto or avrPtoB in the Pseudomonas syringae pathovar tomato. Pto-mediated immunity requires Prf, a host resistance protein with a nucleotide-binding site and a region of leucine-rich repeats. Pto and Prf form a recognition complex in the plant cell and function coordinately in defense signaling. However, how the recognition signal is transduced from Pto/Prf complex to the downstream defense responses is largely unknown. Recently, we have identified SlNAC1, a plant specific transcription factor, interacts with Prf in the yeast two-hybrid assay. The SlNAC1 gene is induced during Pto/Prf-mediated defense response. Interestingly, we found that SlNAC1 is undergoing a regulation of ubiquitin-mediated
degradation. Together, we hypothesize that Prf might function in defense response via direct interaction with transcription factor for transcriptional reprogramming. To further characterize the role of SlNAC1 in disease resistance, we are currently using the combination of molecular, genetic, biochemical and cellular approaches to investigate the role of SlNAC1 in Pto/Prf-mediated resistance and the regulation of SlNAC1. In addition, the possible role of SlNAC1 in PAMP-mediated basal defenses will also be investigated in order to elucidate the signaling crosstalk between these two branches of plant immunity system. Given the fact that NAC transcription factors are highly functionally conserved plant specific transcription factors are involved in many stress responses, the discovery from this study may have broader impact on study of disease resistance mechanisms in other crops,
especially for other economically import crops in Solanaceae family, such as potato, tobacco, and eggplants. We propose the following objectives: 1.Determine the functional relationship between Prf and SlNAC1. 2.Determine the role of SlNAC1 in Pto/Prf-mediated disease resistance. 3.Investigate the regulation of SlNAC1 transcription factor in the plant cell. 4.Explore the downstream genes regulated by SlNAC1. 5.Generate tomato transgenic plants containing engineered variants of the SlNAC1 gene.