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.One way that plants can respond to pathogen infection is through an induced resistance response called R gene resistance. When a plant has an R gene that confers resistance to an infecting pathogen, the plant initiates extensive biochemical and structural defense mechanisms, including the production of phytoalexins and pathogenesis-related proteins, the strengthening of cell walls, local cell death, and systemic acquired resistance (Dangl and Jones, 2001). Plants that are "susceptible," i.e. do not have R gene resistance to a particular pathogen strain, exhibit many defenses similar to R gene resistance, but are slower in their expression of these responses (Yang et al., 1997;Maleck et al., 2000). Like R gene-resistant plants, susceptible plants have increased levels of salicylic acid (SA; O'Donnell et al., 2001), cell death, and defense mechanisms characteristic of systemic acquired resistance (Glazebrook, 2001). In addition, infected, susceptible plants can exhibit increased levels of jasmonic acid (JA), auxin, and ethylene (Dong, 1998;Lund et al., 1998;O'Donnell et al., 2003).These responses of plants to pathogen infection bear some similarity to responses to abiotic stress. Both can involve cell death (Beers and McDowell, 2001), ethylene, SA, and JA (Wang et al., 2002) and cause changes in the expression of some of the same transcription factors (Chen et al., 2002). One way in which plants respond to abiotic stresses is to accelerate their transition to reproduction. Researchers have noted that plants flower faster in response to shade, overcrowding, low nutrients, drought, heat, and low light quality (Casal ...

Genetic architecture of Arabidopsis thaliana response to infection by Pseudomonas syringae

“…The direction and magnitude of selection on rosette size and flowering time is similar to what has been reported in other studies (reviewed in Pigliucci, 2003). Selection for less bacterial growth is not surprising considering that infection by P. syringae has been shown to reduce fitness in A. thaliana in other studies (Kover and Schaal, 2002;Korves and Bergelson, 2003). However, the positive relationship between symptom severity and fitness is very surprising.…”

“…As with any other selection study, the observed patterns of selection are dependent on the environmental conditions experienced by the plants in the growth chamber and only reflect plant response to infection at a specific developmental stage. Although no phenotypic correlation was observed between either rosette size or flowering time and the two susceptibility-related traits in our study, other studies have shown that infected plants tend to flower earlier than uninfected plants (Peters, 1999;Korves and Bergelson, 2003). Since we found that selection favors earlier flowering in infected plants, it is possible that selection on tolerance-related traits (ie traits that alter the effect of infection on fitness) are more important than resistance-related traits (ie traits that affect the degree to which plants become infected).…”

Mechanisms of Nuclear Suppression of Host Immunity by Effectors from the Arabidopsis Downy Mildew Pathogen Hyaloperonospora arabidopsidis (Hpa)

“…Hyaloperonospora arabidopsidis (Hpa)-infected plants show curving of the leaves (Fig. 1) and early flowering (Korves and Bergelson 2003). Interestingly, in response to different plant pathogens, a similar developmental phenotype can be observed.…”

“…Plant parasitic nematodes as well as Xanthomonas provoke plant cell hyperplasia and hypertrophy (Caillaud et al 2008;Kay and Bonas 2009). In response to Pst, Xanthomonas, and Hpa, plants reduce time to flower and the number of aerial branches on the primary inflorescence (Korves and Bergelson 2003). These changes are prevented in a resistant plant, such as one carrying RPS2 (Korves and Bergelson 2003).…”

“…In response to Pst, Xanthomonas, and Hpa, plants reduce time to flower and the number of aerial branches on the primary inflorescence (Korves and Bergelson 2003). These changes are prevented in a resistant plant, such as one carrying RPS2 (Korves and Bergelson 2003).…”