Abstract
Plants depend on innate immune responses to retard the initial spread of pathogens entering through stomata, hydathodes or injuries. These responses are triggered by conserved patterns in pathogen-encoded molecules known as pathogen-associated molecular patterns (PAMPs). Production of reactive oxygen species (ROS) is one of the first responses, and the resulting ‘oxidative burst’ is considered to be a first line of defense. In this study, we conducted association analyses between ROS production and bacterial spot (BS; Xanthomonas spp.) resistance in 63 genotypes of tomato (Solanum lycopersicum L.). A luminol-based assay was performed on leaf tissues that had been treated with a flagellin 22 (flg22), flagellin 28 and a Xanthomonas-specific flg22 (flg22-Xac) peptide, to measure PAMP-induced ROS production in each genotype. These genotypes were also assessed for BS disease response by inoculation with Xanthomonas perforans, race T4. Although there was no consistent relationship between peptides used and host response to the BS, there was a significant negative correlation (r=−0.25, P<0.05) between foliar disease severity and ROS production, when flg22-Xac was used. This response could potentially be used to identify the Xanthomonas-specific PRR allele in tomato, and eventually PAMP-triggered immunity loci could be mapped in a segregating population. This has potential significance in tomato improvement.
Highlights
Tomato (Solanum lycopersicum L.) is the second most important vegetable crop in the world, as well as being an important model plant for genetics and genomics studies because of its relatively short reproductive cycle and small genome
Non-significant correlations are shown in Figures 2b and c. By screening such a large number of diverse tomato lines, this study identified plants with a broad range of responses to Bacterial spot (BS) caused by X. perforans race T4
We observed a wide range of responses to the three pathogen-associated molecular patterns (PAMPs) by the 63 tomato lines used here, perhaps not surprisingly, there was no correlation between flg[22] and flgII-28, resultant reactive oxygen species (ROS) production and BS disease severity
Summary
Tomato (Solanum lycopersicum L.) is the second most important vegetable crop in the world, as well as being an important model plant for genetics and genomics studies because of its relatively short reproductive cycle and small genome. In turn, evolved mechanisms to identify and block the effect of these specific effectors and limit infection. Together, this interaction is known as effector-triggered immunity,[3,12] which is more effective than PTI. PTI responses include production of reactive oxygen species (ROS), protein phosphorylation, ethylene biosynthesis and cell wall reinforcement by callose deposition.[11,13,14,15,16]
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