Expression Divergence as an Evolutionary Alternative Mechanism Adopted by Two Rice Subspecies Against Rice Blast Infection

Background: Rice (Oryza sativa L.) is one of the most important crops that serves as staple food for ~ 50% of the human population worldwide. Some important agronomic traits that allow rice to cope with numerous abiotic and biotic stresses have been selected and fixed during domestication. Knowledge on how expression divergence of genes gradually contributes to phenotypic differentiation in response to biotic stress and their contribution to rice population speciation is still limited.

Results: Here, we explored gene expression divergence between a japonica rice cultivar Nipponbare and an indica rice cultivar 93-11 in response to invasion by the filamentous ascomycete fungus Magnaporthe oryzae (Pyricularia oryzae), a plant pathogen that causes significant loss to rice production worldwide. We investigated differentially expressed genes in the two cultivars and observed that evolutionarily conserved orthologous genes showed highly variable expression patterns under rice blast infection. Analysis of promoter region of these differentially expressed orthologous genes revealed the existence of cis-regulatory elements associated with the differentiated expression pattern of these genes in the two rice cultivars. Further comparison of these regions in global rice population indicated their fixation and close relationship with rice population divergence.

Conclusion: We proposed that variation in the expression patterns of these orthologous genes mediated by cis-regulatory elements in the two rice cultivars, may constitute an alternative evolutionary mechanism that distinguishes these two genetically and ecologically divergent rice cultivars in response to M. oryzae infection.