Phytophthora Infestans - Genetics

Genetics

In 2009 scientists completed the sequencing of the genome of P. infestans. It was found that the genome is considerably larger (240 Mbp) compared to other Phytophthora species whose genomes have been sequenced; Phytophthora sojae has a 95 Mbp genome and Phytophthora ramorum had a 65 Mbp genome. It also contained a diverse variety of transposons and many gene families encoding for effector proteins that are involved in causing pathogenicity. These proteins are split into two main groups depending on whether they are produced by the water mould in the symplast (inside plant cells) or in the apoplast (between plant cells). Proteins produced in the symplast included RXLR proteins, which contain an arginine-X-leucine-arginine (where X can be any amino acid) sequence at the amino terminus of the protein. RXLR proteins are avirulence proteins, meaning that they can be detected by the plant and lead to a hypersensitive response, killing the oomycete. P. infestans was found to contain around 60% more of these proteins than other Phytophthora species and this may allow it to overcome host defences more quickly. Those found in the apoplast include hydrolytic enzymes such as proteases, lipases and glycosylases that act to degrade plant tissue, enzyme inhibitors to protect against host defence enzymes and necrotizing toxins. Overall the genome was found to have an extremely high repeat content (around 74%) and to have an unusual gene distribution in that some areas contain many genes whereas others contain very few.