Abstract
Using a genome-wide approach, we asked how many transporter genes contribute to symbiotic phosphate uptake and analyzed their evolutionary conservation. Considering the sequenced rice genome at hand, only the Oryza sativa phosphate transporter (OsPT) gene OsPT11 was specifically induced during the arbuscular mycorrhizal symbiosis. This induction was confined to the root system and was tightly correlated with the degree of root colonization by Glomus intraradices. OsPT11 activation was independent of the nutritional status of the plant and phosphate availability in the rhizosphere. Moreover, infection of roots with the fungal pathogens Rhizoctonia solani and Fusarium moniliforme did not activate OsPT11, corroborating the high signal specificity for OsPT11 activation in the arbuscular mycorrhizal symbiosis. OsPT11 expression complemented a defect in phosphate uptake in a yeast strain mutated in its high-affinity P(i) transporter (pho84), thereby confirming its function. Recently, a phosphate transporter gene in potato was shown to be induced during arbuscular mycorrhizal symbiosis. Assessment of the phylogenetic relationship of the rice and potato protein revealed that the rice is nonorthologous to the potato protein. Further, there are no structural commonalities in the promoter regions. Thus, although cytological and physiological features of the arbuscular mycorrhizal symbiosis seem to be conserved, the molecular components may differ significantly between distantly related plant species.