Isolation and functional characterization of LePT4, a mycorrhizal enhanced phosphate transporter in tomato

摘要

Plant roots acquire inorganic phosphate (Pi) from soils by two major routes: either directly from root-soil interface via high affinity Pi transporters in roots or through symbiotic associations between the cortical cells of roots and ectomycorrhizal or arbuscular mycorrhizal fungi. In this study, v/e isolated and characterized LePT4, a gene encoding a novel Pi transporter in tomato. To further elucidate the in planta role of this Pi transporter, we identified and characterized a corresponding loss-of-function mutant in tomato. In the absence of mycorrhizal infection and under sufficient Pi concentration (1 mM), LePT4 expression was very low in the wild type and a mutation in this gene reduced total Pi accumulation only slightly. A P-starved lept4 mutant exhibited severe P-deficiency symptoms and its Pi uptake was significantly lower than that of the wild type. Under low Pi availability, mycorrhizal infection of the wild type resulted in a significant increase in the transcripts of LePT4 and a concomitant twofold increase in Pi accumulation. lept4 infected with mycorrhiza also exhibited increased Pi accumulation, although to a significantly lower extent than that observed for the wild type. These data highlight the role of LePT4 in mycorrhizal-mediated Pi uptake in tomato. In addition, we also identified LePT3 in tomato which is orthologous to StPT3 in potato and showed higher transcript levels upon mycorrhizal infection. LePT3 may represent an alternative route for Pi uptake in mycorrhiza-colonized roots. To our knowledge lept4 is the first characterized phosphate transporter mutant associated with mycorrhizae in plants. This mutant, together with the isolation and characterization of LePT3, provides evidence for the different routes of mycorrhiza-mediated Pi uptake in plants.