De novo asparagine biosynthesis by Magnaporthe oryzae is required for fungal proliferation in rice cells  
M. MARROQUIN-GUZMAN (1), R. Wilson (1) (1) University of Nebraska-Lincoln, U.S.A.

Magnaporthe oryzae is one of the most devastating rice pathogens. However, the metabolic strategies employed by this pathogen during in planta growth are unknown. To understand what host-derived nutrients might facilitate rice cell invasion, we focused on the M. oryzae gene ASN1 encoding an enzyme that converts aspartate to asparagine in a single step. Dasn1 mutant strains were unable to grow on media lacking asparagine, confirming Asn1 is required for asparagine biosynthesis. Spores of Dasn1 mutant strains formed functional appressoria that penetrated into epidermal cells at the same rate as wild type. However, Dasn1 mutant strains were impaired in cell-to-cell movement and did not form lesions on the leaves of rice seedlings. In contrast, ASP1, encoding an asparaginase that catalyzes the production of aspartate from asparagine, was dispensable for pathogenicity. Our data suggests that de novo asparagine biosynthesis by M. oryzae via aspartate is essential for biotrophy, and that, conversely, asparagine is not acquired from the host during early  infection. This study thus reveals an important metabolic strategy to facilitate host rice cell invasion by M. oryzae whereby TCA cycle intermediates, in this case oxaloacetate, provide the carbon backbone for asparagine biosynthesis via aspartate in preference to the direct acquisition of asparagine from the host. 

Abstract Number: P7-192
Session Type: Poster