Title: Co-evolution of chitinases from maize and other cereals with secreted proteases from Pleosporineae fungi Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 24, 2013
Publication Date: N/A
Technical Abstract: Plant class IV chitinases are composed of a carboxy-terminal chitinase domain that is attached, through a linker sequence, to a small amino-terminal domain that can be thought of as a structured peptide. While both the peptide-like domain and the chitinase domain share sequence homology throughout monocot and dicot chitinases, the linker sequences that tether them are divergent. Here we show evidence that polyglycine linker sequences, which are specific to chitinases in cereals and related plants, co-evolved with secreted proteases from fungal pathogens. Proteases secreted by the maize pathogen Cochliobolus carbonum and the sorghum pathogen Phoma sorghina were purified. MALDI-TOF mass spectrometry analysis of product peptides from in vitro reactions with maize ChitA chitinase showed that these proteases cleave peptide bonds within the ChitA polyglycine linker. The ChitA isoform ChitB, in which the polyglycine sequence is interupted by two consecutive serines, was found to be resistant to truncation by the protease from C. carbonum but not the protease from P. sorghina. When these serine amino acids were mutated to glycines, ChitB became susceptible to truncation by both hydrolases. Our findings demonstrate that the serine residues that interupt the maize ChitB polyglycine linker make it resistant to some fungal proteases and suggest that some pathogen proteases have evolved to overcome this resistance.