Skip to main content
eScholarship
Open Access Publications from the University of California

UC Berkeley

UC Berkeley Electronic Theses and Dissertations bannerUC Berkeley

Bacterial growth in the plant apoplast is limited by nutrient availability

Abstract

Bacterial ability to multiply endophytically (inside leaves) is an intrinsic trait of bacterial plant pathogens such as Pss B728a and Pto DC3000. Type III secretion system (TTSS)-possessing pathogens multiply endophytically to large population sizes (>108-109cfu/g). Non-pathogenic strains such as the saprophytes Pantoea agglomerans and Pseudomonas fluorescens, and hrp/hrc cluster mutants (TTSS mutants) mostly fail to multiply endophytically. The growth-restricting activity of the plant defense surveillance system is thought to restrict growth of non-pathogens inside the leaves through a series of responses that induce deposition of callose, reactive oxygen species production, and production of a variety of antimicrobials. This process is collectively known as PTI (pathogen-associated molecular pattern-triggered immunity). However we found several treatments that induce high sugar availability in the apoplast to elicit a dramatic growth of various non-pathogenic strains. Saprophytes and hrp mutants growing in both host and non-host plants multiplied up to 10,000-fold either when co infiltrated into plants with utilizable (i.e. metabolized substrates in vitro) carbon sources, infiltrated with water alone while water-soaking conditions maintained or when co-infiltrated with a TTSS-proficient pathogen. Pathogens were not limited in growth by carbon sources since they carry TTSS effectors that they can deploy to provide them with needed resources. We thus propose that similarly to bacteria growing in the surface of leaves, availability and distribution of sugars are the main limiting factors for endophytic bacteria, and while TTSS-proficient pathogens can alter the plant to obtain apoplastic nutrients, non-pathogenic strains cannot.

Main Content
For improved accessibility of PDF content, download the file to your device.
Current View