A 1-phytase type III effector interferes with plant hormone signaling

Abstract

Most Gram-negative phytopathogenic bacteria inject type III effector (T3E) proteins into plant cells to manipulate signaling pathways to the pathogen’s benefit. In resistant plants, specialized immune receptors recognize single T3Es or their biochemical activities, thus halting pathogen ingress. However, molecular function and mode of recognition for most T3Es remains elusive. Here, we show that the Xanthomonas T3E XopH possesses phytase activity, i.e., dephosphorylates phytate (myo-inositol-hexakisphosphate, InsP6), the major phosphate storage compound in plants, which is also involved in pathogen defense. A combination of biochemical approaches, including a new NMR-based method to discriminate inositol polyphosphate enantiomers, identifies XopH as a naturally occurring 1-phytase that dephosphorylates InsP6 at C1. Infection of Nicotiana benthamiana and pepper by Xanthomonas results in a XopH-dependent conversion of InsP6 to InsP5. 1-phytase activity is required for XopH-mediated immunity of plants carrying the Bs7 resistance gene, and for induction of jasmonate- and ethylene-responsive genes in N. benthamiana.

Ethylene and 1-Aminocyclopropane-1-carboxylate (ACC) in Plant–Bacterial Interactions

“…On the other hand, Liu et al (2011) showed that the Erwinia amylovora -derived elicitor HrpNEa activates the transcription factor MYB44, which in turn enhances the expression of EIN2 . Recently, Blüher et al (2017) demonstrated that Xanthomonas campestris pv. vesicatoria produces a type III secretion effector, XopH, that possesses phytase activity and modulates the Nicotiana benthamiana defense response.…”

Identity and functions of inorganic and inositol polyphosphates in plants

“…InsPs have been further implicated in plant immune signaling by the characterization of the Xanthomonas campestris effector protein XopH as phytase (InsP 6 phosphatase) (Bl€ uher et al, 2017). Ectopic expression of XopH in N. benthamiana indeed resulted in reduced InsP 6 , InsP 7 and InsP 8 concentrations (Bl€ uher et al, 2017).…”

Functional Metagenomics Reveals an Overlooked Diversity and Novel Features of Soil-Derived Bacterial Phosphatases and Phytases

“…This is especially the case for phosphatases. Phosphatases have evolved across all living organisms and contribute to the regulation of diverse cellular functions (5, 6). A specific group of phosphatases named phytases can release phosphorus from phytic acid, which is one of the most important phosphorus reserves in plants and soils (7, 8).…”

“…These enzymes are currently used in agroindustry to minimize P losses and to improve the levels of bioavailable P (14). A more recently described role of the phytases is their involvement in pathogenicity causing tissue damage in humans, coordination of the virulence program in Dickeya dadantii, and mediation of plant infection by Candida albicans and Xanthomonas , respectively (5, 15, 16).…”