Horizontally acquired fungal killer protein genes affect cell development in mosses

The moss Physcomitrium patens is crucial for studying plant development and evolution. Although the P. patens genome includes genes acquired from bacteria, fungi and viruses, the functions and evolutionary significance of these acquired genes remain largely unclear. Killer protein 4 (KP4) is a well-studied toxin secreted by ascomycete fungi, such as the corn smut Ustilago maydis, which inhibits the growth of sensitive target strains by blocking their calcium uptake. Here, we show that KP4 genes in mosses were acquired from fungi through at least three independent events of horizontal gene transfer. Two paralogous copies of KP4 (PpKP4-1 and PpKP4-2) exist in P. patens. Knockout mutants ppkp4-1 and ppkp4-2 showed cell death at the protonemal stage, and ppkp4-2 also exhibited defects in tip growth. We provide experimental evidence indicating that PpKP4-1/2 affects P. patens protonemal cell development by mediating cytoplasmic calcium and that KP4 genes are functionally conserved between P. patens and fungi. The present study provides additional insights into the role of horizontal gene transfer in land plant development and evolution.

Automated summary

The moss Physcomitrium patens is essential for understanding plant development and evolution. It contains genes acquired from bacteria, fungi, and viruses, but the functions and significance of these acquired genes are still unclear. This study shows that KP4 genes in mosses were obtained from fungi through multiple horizontal gene transfer events. Knockout mutants of these genes in P. patens showed cell death and growth defects. Experimental evidence suggests that PpKP4-1/2 affects P. patens cell development by regulating cytoplasmic calcium, and that KP4 genes are conserved between P. patens and fungi. This study provides new insights into the role of horizontal gene transfer in land plant development and evolution.