Plant Stomata Function in Innate Immunity against Bacterial Invasion

Abstract

Microbial entry into host tissue is a critical first step in causing infection in animals and plants. In plants, it has been assumed that microscopic surface openings, such as stomata, serve as passive ports of bacterial entry during infection. Surprisingly, we found that stomatal closure is part of a plant innate immune response to restrict bacterial invasion. Stomatal guard cells of Arabidopsis perceive bacterial surface molecules, which requires the FLS2 receptor, production of nitric oxide, and the guard-cell-specific OST1 kinase. To circumvent this innate immune response, plant pathogenic bacteria have evolved specific virulence factors to effectively cause stomatal reopening as an important pathogenesis strategy. We provide evidence that supports a model in which stomata, as part of an integral innate immune system, act as a barrier against bacterial infection.

Requirement of Vesicle-Associated Membrane Protein 721 and 722 for Sustained Growth during Immune Responses in Arabidopsis

“…The FLS2 receptor, which detects the presence of bacterial flagellin, is known to restrict bacterial growth in part by limiting entry of the bacteria into the leaf interior through stomata (Melotto et al, 2006;Zipfel et al, 2004). To test a potential involvement of VAMP721/722 in growth during MTI, we first examined FLS2 receptor-dependent growth inhibition in 7 dayold seedlings upon treatment with flg22, the elicitor-active peptide derived from flagellin (Gomez-Gomez et al, 1999).…”

On plant defense signaling networks and early land plant evolution

“…The latter is more specific towards the infecting pathogen because plant resistance genes ( R genes) recognize effector proteins secreted by, and specific to, a certain pathogen [51]. PTI causes, for example, stomata closure and cell wall reinforcements at the site of pathogen attack (e.g., through callose deposition, formation of papillae [deposits consisting of callose, phenolic compounds and polysaccharides], and lignification) [52-55]. PTI can also result in cell death caused by the release of reactive oxygen species (ROS) [56].…”

The multifaceted role of ABA in disease resistance

“…Other pathogens instead use pre-existing openings, such as stomata or wounds ( Figure 1, Phase I). Plants can increase their pre-invasive penetration resistance by closing stomata rapidly upon perception of microbes, which occurs within 1 h after inoculation with pathogenic and non-pathogenic bacteria [8]. This defense response can be mimicked by application of pathogen-associated molecular patterns (PAMPs), such as the flagellin derivative flg22 and lipopolysacharides.…”