Malate : Quinone Oxidoreductase and Malic Enzyme are required for the Plant Pathogen Pseudomonas syringae pv. tomato DC3000 to Utilize Malate

Abstract

Pseudomonas syringae pv. tomato strain DC3000 (DC3000) is a gram-negative bacterial plant pathogen that causes disease on tomato and the model plant Arabidopsis thaliana. Interestingly, previous studies showed that malate:quinone oxidoreductase (Mqo), an enzyme in the citric acid cycle, is required for DC3000 to cause disease on these plants. In addition, growth of DC3000 lacking the mqo gene in minimal medium with malate was significantly delayed, but eventually reached wild-type levels of growth, which is similar to growth in planta. This suggests that malate may be an important carbon source for DC3000. One reason the mqo::KO bacteria may be able to reach wild-type levels of growth in culture and plants is that the DC3000 malic enzyme may be used to complete the citric acid cycle. Our research shows that a mutant strain lacking a functional mqo gene and malic enzyme gene (mqo::KO;ME::pJP) fails to grow in minimal media cultures with malate and has reduced growth in media with citrate, indicating that both Mqo and ME are required for normal growth when utilizing these carbon sources. Future studies looking at growth of this double mutant in plants will identify how important the activities of both of these genes are for DC3000 to cause disease in plants. KEY WORDS: Malate:quinone Oxidoreductase; Malic Enzyme; MQO; Pseudomonas syringae; Arabidopsis thaliana; Malate; Citrate; DC3000