Balancing Vitamin B6 Homeostasis for Plant Immunity.

Vitamin B6 (VB6), a metabolic cofactor, is essential for plants, animals, and microorganisms. VB6 has emerged as an important regulator of plant immunity, modulating various immune responses, including basal immunity, stomatal defence, and induced systemic resistance. However, the role of VB6 in systemic acquired resistance (SAR) and the active VB6 vitamers involved in modulating plant immunity remain unclear. A recent study reveals that Δ1-piperideine-6-carboxylic acid (P6C), a metabolite from lysine catabolism, sequesters VB6 vitamers, such as pyridoxal (PL) and pyridoxal 5'-phosphate (PLP), into inert complexes. This depletion of active VB6 vitamers disrupts VB6 homeostasis, impairing SAR, while exogenous application of VB6 restores resistance. Interestingly, the resemblance of this mechanism to pyridoxine-dependent epilepsy in humans suggests evolutionary conservation of these metabolic processes. This article explores the multifaceted roles of VB6 in different aspects of plant immunity. We emphasise the need for further research to decode the complex interplay between VB6 homeostasis and defence hormone pathways to deepen our understanding of immune signalling and develop new strategies to enhance stress resilience in plants.