Cytoplasmic sequestering of a fungal stress-activated MAPK in response to a host plant phenolic acid

Abstract

The stress-activated MAPK Hog1 in Cochliobolus heterostrophus, a maize foliar pathogen, undergoes dephosphorylation upon exposure to ferulic acid (FA), a phenolic compound abundant in the host plant. Unlike its nuclear localization during osmotic stress, Hog1:GFP forms cytoplasmic foci in response to FA, indicating its sequestering. By using Hog1:GFP as an affinity purification bait, we isolated an FA-dependent sub-proteome from a subcellular fraction enriched with fluorescent foci. The identified proteins include RNA-binding proteins, translation initiation factors and mitochondrial proteins, suggesting the foci to be stress granules. Notably, the RRM and pumilio domain protein Puf2 was enriched, and Puf2:tdTomato formed foci partially colocalizing with Hog1:GFP foci. Hog1:GFP did not colocalize with peroxisomes. Mitochondria, however, which rapidly fragmented upon FA exposure, are partially overlapped with Hog1:GFP foci. The sequestering and dephosphorylation of MAPK Hog1 may collectively attenuate cell death induced by defense compounds released by the plant host.