Heterologous expression of the avirulence gene ACE1 from the fungal rice pathogen Magnaporthe oryzae

Abstract

The <i>ACE1</i> and <i>RAP1</i> genes from the avirulence signalling gene cluster of the rice blast fungus <i>Magnaporthe oryzae</i> were expressed in <i>Aspergillus oryzae</i> and <i>M. oryzae</i> itself. Expression of <i>ACE1</i> alone produced a polyenyl pyrone (magnaporthepyrone), which is regioselectively epoxidised and hydrolysed to give different diols, <b>6</b> and <b>7</b>, in the two host organisms. Analysis of the three introns present in <i>ACE1</i> determined that <i>A. oryzae</i> does not process intron 2 correctly, while <i>M. oryzae</i> processes all introns correctly in both appressoria and mycelia. Co-expression of <i>ACE1</i> and <i>RAP1</i> in <i>A. oryzae</i> produced an amide <b>8</b> which is similar to the PKS-NRPS derived backbone of the cytochalasans. Biological testing on rice leaves showed that neither the diols <b>6</b> and <b>7</b>, nor amide <b>8</b> was responsible for the observed <i>ACE1</i> mediated avirulence, however, gene cluster analysis suggests that the true avirulence signalling compound may be a tyrosine-derived cytochalasan compound.