Hydrogen sulphide: an emerging regulator of plant defence signalling.

Hydrogen sulphide (H 2 S), a gaseous signalling molecule in plants, has gained considerable attention in recent years because of its emerging roles in the regulation of plant growth and development and responses to abiotic stressors. Although the involvement of H 2 S in biotic stress is not well documented in the literature, a growing body of evidence indicates its potential role in plant defence, particularly against bacterial and fungal pathogens. Recent reports have suggested that H 2 S participates in plant defence signalling potentially by (1) regulating glutathione metabolism, (2) inducing expression of pathogenesis-related (PR) and other defence-related genes, (3) modulating enzyme activity through post-translational modifications, and (4) interacting with phytohormones such as jasmonic acid, ethylene and auxin. In this review, we discuss the biosynthesis, metabolism and interaction of H 2 S with phytohormones, and highlight evidence gathered so far to support the emerging roles of H 2 S in plant defence against invading pathogens.