Solanaceous species are among the>200 000 plant species worldwide forming a mycorrhiza, that is, a root living in symbiosis with soil-borne arbuscular-mycorrhizal (AM) fungi. An important parameter of this symbiosis, which is vital for ecosystem productivity, agriculture, and horticulture, is the transfer of phosphate (Pi) from the AM fungus to the plant, facilitated by plasma membrane-spanning Pi transporter proteins. The first mycorrhiza-specific plant Pi transporter to be identified, was StPT3 from potato [Nature414(2004) 462]. Here, we describe novel Pi transporters from the solanaceous species tomato, LePT4, and its orthologue StPT4 from potato, both being members of the Pht1 family of plant Pi transporters. Phylogenetic tree analysis demonstrates clustering of both LePT4 and StPT4 with the mycorrhiza-specific Pi transporter fromMedicago truncatula[Plant Cell,14(2002) 2413] and rice [Proc. Natl Acad. Sci. USA,99(2002) 13324], respectively, but not with StPT3, indicating that two non-orthologous mycorrhiza-responsive genes encoding Pi transporters are co-expressed in the Solanaceae. The cloned promoter regions from both genes,LePT4andStPT4, exhibit a high degree of sequence identity and were shown to direct expression exclusively in colonized cells when fused to the GUS reporter gene, in accordance with the abundance ofLePT4andStPT4transcripts in mycorrhized roots. Furthermore, extensive sequencing ofStPT4-like clones and subsequent expression analysis in potato and tomato revealed the presence of a close paralogue ofStPT4andLePT4, namedStPT5andLePT5, respectively, representing a third Pi transport system in solanaceous species which is upregulated upon AM fungal colonization of roots. Knock out ofLePT4in the tomato cv. MicroTom indicated considerable redundancy between LePT4 and other Pi transporters in tomato. [ABSTRACT FROM AUTHOR]