A developmental response to pathogen infection in Arabidopsis

Abstract

We present evidence that susceptible Arabidopsis plants accelerate their reproductive development and alter their shoot architecture in response to three different pathogen species. We infected 2-week-old Arabidopsis seedlings with two bacterial pathogens, Pseudomonas syringae and Xanthomonas campestris, and an oomycete, Peronospora parasitica. Infection with each of the three pathogens reduced time to flowering and the number of aerial branches on the primary inflorescence. In the absence of competition, P. syringae and P. parasitica infection also increased basal branch development. Flowering time and branch responses were affected by the amount of pathogen present. Large amounts of pathogen caused the most dramatic changes in the number of branches on the primary inflorescence, but small amounts of P. syringae caused the fastest flowering and the production of the most basal branches. RPS2 resistance prevented large changes in development when it prevented visible disease symptoms but not at high pathogen doses and when substantial visible hypersensitive response occurred. These experiments indicate that phylogenetically disparate pathogens cause similar changes in the development of susceptible Arabidopsis. We propose that these changes in flowering time and branch architecture constitute a general developmental response to pathogen infection that may affect tolerance of and/or resistance to disease.

Figure 1.

Effect of amount of pathogen present per infected leaf 4 d after infection. Black circles, Means for the compatible and non-host P. syringae strain dose combinations. Solid line, Regression line through these data. White circles, Three dose treatments for DC3000 + avrRpt2 to which the plants have R gene resistance. Rectangles, Three X. campestris dose treatments. The letters beside the markers indicate the strain (D, DC3000; E, ES4326; N, NPS3121; R, RM18.1; A, DC3000 + avrRpt2; X, X. campestris 8004) and dose (Low, Medium, and rHigh). Dashed line, Value of the trait for the mock treatment, which does not have a corresponding pathogen amount. Plants are wild-type Col. Each point is a mean of 19 replicates. A, Percentage of infected leaf area with disease symptoms 9 d after infection. B, Number of days to bolting. C, Number of secondary aerial meristems.

Figure 2.

Mean numbers of days to flowering, aerial branches, and basal branches for rps2 plants grown in large pots and infected with a low, medium, or high dose of P. syrinage DC3000 + pLABL18 (OD₆₀₀= 0.0001, 0.0003, and 0.001, respectively) or a mock treatment. Error bars = ses. Letters denote differences between treatments for P < 0.05.