Erwinia amylovora Expresses Fast and Simultaneously hrp/dsp Virulence Genes during Flower Infection on Apple Trees

PLoS One

Eva Wilhelm¹  Renáta Milčevičová¹  Sylvia Blümel²  Doris Pester²  Johann Schaffer² 

[1]Health and Environment, Austrian Institute of Technology (AIT), Seibersdorf, Austria

[2]Institute of Plant Health, Austrian Agency for Health and Food Safety (AGES), Vienna, Austria

关键词: Flowers;    Gene expression;    Secretion systems;    Plant bacterial pathogens;    Apples;    Flowering plants;    Plant defenses;    Plant pathogens;   

DOI  :  10.1371/journal.pone.0032583

学科分类：医学（综合）

来源: Public Library of Science

【 摘 要 】

Background Pathogen entry through host blossoms is the predominant infection pathway of the Gram-negative bacterium Erwinia amylovora leading to manifestation of the disease fire blight. Like in other economically important plant pathogens, E. amylovora pathogenicity depends on a type III secretion system encoded by hrp genes. However, timing and transcriptional order of hrp gene expression during flower infections are unknown. Methodology/Principal Findings Using quantitative real-time PCR analyses, we addressed the questions of how fast, strong and uniform key hrp virulence genes and the effector dspA/E are expressed when bacteria enter flowers provided with the full defense mechanism of the apple plant. In non-invasive bacterial inoculations of apple flowers still attached to the tree, E. amylovora activated expression of key type III secretion genes in a narrow time window, mounting in a single expression peak of all investigated hrp/dspA/E genes around 24–48 h post inoculation (hpi). This single expression peak coincided with a single depression in the plant PR-1 expression at 24 hpi indicating transient manipulation of the salicylic acid pathway as one target of E. amylovora type III effectors. Expression of hrp/dspA/E genes was highly correlated to expression of the regulator hrpL and relative transcript abundances followed the ratio: hrpA>hrpN>hrpL>dspA/E. Acidic conditions (pH 4) in flower infections led to reduced virulence/effector gene expression without the typical expression peak observed under natural conditions (pH 7). Conclusion/Significance The simultaneous expression of hrpL, hrpA, hrpN, and the effector dspA/E during early floral infection indicates that speed and immediate effector transmission is important for successful plant invasion. When this delicate balance is disturbed, e.g., by acidic pH during infection, virulence gene expression is reduced, thus partly explaining the efficacy of acidification in fire blight control on a molecular level.

【 授权许可】

CC BY