Understanding the interplay between the grass-endophyte mutualism and the host plant genetic variability

GUNDEL, PE; OMACINI M; GHERSA, CM

Buenos Aires

Simposio; International Symposium on Molecular Breeding of Forage & Turf; 2010

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Plant-microbes interactions may potentially affect fitness and evolution of involved species. Therefore, it is interesting to understand the underlying mechanisms that maintain mutualistic interactions (i.e. both partners are benefited) under natural and human selection. Endophytes of genus Neotyphodium are mutualist fungi that protect cool-season grasses against biotic and abiotic stresses. However, it has been claimed that the mutualism would only be expressed in agronomic grasses that have been subjected to selection. Instead, the differential gene flow rate between partner’s populations is expected to disrupt the genetic specificity and hence the mutualism in wild grasses. Here we propose a model that incorporates others essential elements that are important for the interaction which are the “genetic specificity” and “mutualism effectiveness”, and “host fitness” and “endophyte transmission efficiency”. In this model, gene flow is viewed as a source of genetic variability promoting host fitness and raw material for evolution. Since endophytes reproduce clonally and depend on hosts for multiplication and dissemination, we propose that the endophyte-grass interaction works as an integrated entity. Despite the apparent trade-off between genetic specificity and host fitness in relation to the genetic distance among mating parents, the model assumes that a certain level of heterosis is needed for the mutualism effectiveness. Although genetic specificity could be the highest at low genetic distance among mating parents, the mutualism effectiveness and the transmission efficiency will be low in inbreeding depressed hosts. According with the increment in the genetic distance among mating parents, the mutualism effectiveness and the transmission efficiency will also be increased. However, this relationship will be positive until a level where genetic specificity is really disrupted because the genetic distance among mating parent is extremely high (out-breeding depression). By testing the predictions emergent from the model, we will take advantage of our understanding of the coevolutionary origin and future directions of the endophyte-grass interaction.