Abstract
Bacterial spot caused by several Xanthomonas sp. is one of the most devastating diseases in tomato (Solanum lycopersicum L.). The genetics of hypersensitive resistance to X. perforans race T3 has been intensively investigated and regulatory genes during the infection of race T3 have been identified through transcriptional profiling. However, no work on isolating regulatory genes for field resistance has been reported. In this study, cDNA-amplified fragment length polymorphism technique was used to identify differentially expressed transcripts between resistant tomato accession PI 114490 and susceptible variety OH 88119 at 3, 4 and 5 days post-inoculation of the pathogen. Using 256 selective primer combinations, a total of 79 differentially expressed transcript-derived fragments (TDFs) representing 71 genes were obtained. Of which, 60 were up-regulated and 4 were down-regulated in both tomato lines, 4 were uniquely up-regulated and 2 were uniquely down-regulated in PI 114490, and 1 was specifically up-regulated in OH 88119. The expression patterns of 19 representative TDFs were further confirmed by semi-quantitative and/or quantitative real time RT-PCR. These results suggested that the two tomato lines activated partly similar defensive mechanism in response to race T3 infection. The data obtained here will provide some fundamental information for elucidating the molecular mechanism of response to race T3 infection in tomato plants with field resistance.
Highlights
Bacterial spot severely affects tomato (Solanum lycopersicum L.) fruit production and quality in both open field and protected area [1]
Small lesions with yellow haloes developed on the leaves of OH 88119 on 5 days post-inoculation (DPI), and subsequently expanded to form large necrotic areas throughout the inoculated leaves in the late stage of the disease (Fig. 1A)
Several loci conferring hypersensitive response (HR) to races T1, T3, or T4 of bacterial spot have been mapped [1,5], and a candidate gene Rx4 conferring HR to race T3 in S. pimpinellifolium accession PI 128216 and genes responding to race T3 in tomato line Hawaii 7981 during the process of HR have been identified [8,16,17], none of these HR genes has been cloned
Summary
Bacterial spot severely affects tomato (Solanum lycopersicum L.) fruit production and quality in both open field and protected area [1]. Due to the existence of multiple pathogen species and races, marginal efficacy of commonly applied chemicals, development of resistance to these chemicals in bacterial populations, and a lack of available disease resistance traits in commercial cultivars, control of the disease has not been effective once epidemics start [5,6]. Exploiting host resistance gene(s) combined with important defense response genes for developing cultivars with durable resistance is considered as an effective approach to manage the disease. The resistance to race T3 of bacterial spot in tomato can be either qualitatively or quantitatively inherited. Two S. pimpinellifolium accessions PI 128216 and LA 1589 as well as one unimproved tomato breeding line Hawaii 7981 show both hypersensitive response (HR) and field resistance to race T3
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