A Phosphate Uptake System Is Required for Pv. Virulence in Soybean

The genes encoding the phosphate uptake system in pv. 12-2 were previously found to be upregulated when in soybean leaves. This study thus explored the role of the phosphate uptake system on its virulence to soybean. While and mutants were greatly impaired in both inciting disease symptoms and growth in soybean, the virulence and growth in soybean of a mutant was not reduced when compared with the wild-type strain. The expression of and was highly induced in phosphate-deficient media. In addition, the expression of , assessed with a fusion to a promoterless ice nucleation reporter gene, was greatly increased in soybean leaves, confirming that the soybean apoplast is a phosphorus-limited habitat for pv. . Global gene expression profiles of and mutants of pv. conducted under phosphate-limitation conditions in vitro, using RNA-seq, revealed that PhoB positively regulated genes involved in signal transduction, the cluster type II secretion system, cell motility, and chemotaxis, while negatively regulating cell wall and membrane biogenesis, DNA replication and recombination and repair, and several genes with unknown function. PhoU also positively regulated the same genes involved in cell motility and chemotaxis. The severity of bacterial pustule disease was decreased in soybean plants grown under high phosphate fertilization conditions, demonstrating that high phosphate availability in soybean plants can affect infection by pv. by modulation of the expression of phosphate uptake systems. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.