Analysis of the Pto gene family and Pto-mediated defense gene expression
Abstract
The Pto gene was originally derived from the wild tomato species Lycopersicon pimpinellifolium and confers resistance to Pseudomonas syringae pv. tomato strains expressing avrPto. The AvrPto protein appears to be secreted into the plant cell where it functions by physically interacting with the Pto protein. The Fen gene is another member of the Pto gene family that confers sensitivity to the insecticide fenthion. I have isolated and characterized the alleles of Pto and Fen from cultivated tomato, L. esculentum, and designated them pto and fen. The pto and fen alleles are transcribed and code for active protein kinases that are 87% and 98% identical to the Pto and Fen protein kinases, respectively. The pto and not the fen kinase phosphorylates a Pto substrate, Pti1. In contrast to Pto, the pto kinase shows impaired interactions with AvrPto and with several Pto-interacting proteins (Pti1, Pti4, and Pti6) in the yeast two-hybrid system. These data suggest that the amino acid substitutions that distinguish pto from Pto interfere with recognition of AvrPto, or with protein-protein interactions involved in the Pto-mediated signal transduction pathways. The Pto kinase interacts with the putative transcription factors (Pti4, Pti5, and Pti6) in the yeast two-hybrid system. Pti5/6 bind to a cis-element (5′-AGCCGCC-3′, the “PR box”) that is present in the promoters of many pathogenesis-related (PR) genes from different plant species. I isolated a tomato osmotin gene that contains two PR boxes in the promoter region. I then demonstrated that transcripts of the osmotin gene and of two other tomato PR genes that contain GCC boxes in their promoter regions rapidly accumulate in Pto-containing tomato plants specifically upon inoculation with P. s. tomato expressing avrPto (i.e., incompatible interaction). Moreover, the greater transcript accumulation of a tomato ACC oxidase gene containing a PR box in its promoter region was only observed in the incompatible interaction. These data suggest that the tomato Pto kinase regulates the expression of certain defense genes by interaction with transcription factors that bind the PR box.
Degree
Ph.D.
Advisors
Martin, Purdue University.
Subject Area
Agronomy|Plant pathology|Botany|Molecular biology
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