Summary 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 from Medicago 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, LePT4 and StPT4, 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 of LePT4 and StPT4 transcripts in mycorrhized roots. Furthermore, extensive sequencing of StPT4‐like clones and subsequent expression analysis in potato and tomato revealed the presence of a close paralogue of StPT4 and LePT4, named StPT5 and LePT5, respectively, representing a third Pi transport system in solanaceous species which is upregulated upon AM fungal colonization of roots. Knock out of LePT4 in the tomato cv. MicroTom indicated considerable redundancy between LePT4 and other Pi transporters in tomato.

Wood is the most abundant biological resource on earth and it is also an important raw material for a major global industry with rapidly increasing demand. The genus Eucalyptus includes the most widely used tree species for industrial plantation, mainly for making pulp and paper. With the aim of identifying major genes involved in wood formation in Eucalyptus , we have developed a targeted approach of functional genomics based on the isolation of xylem preferentially expressed genes by subtractive PCR. Transcript profiling using cDNA arrays and analysis of variance (ANOVA) were used to identify differentially expressed ESTs between secondary xylem and leaves. Real-time RT-PCR was performed to confirm the differential expression of representative EST. Of 224 independent EST sequences obtained, 81% were preferentially expressed in xylem. One-third of the ESTs exhibiting homologies with proteins of known function fell into two main classes highlighting the importance of the auxin signalling through ubiquitin-dependent proteolysis on one hand, and of the enzymes involved in cell wall biosynthesis and remodelling, on the other. The functions of the genes represented by the remaining 61% of ESTs should be of great interest for future research. This systematic analysis of genes involved in wood formation in Eucalyptus provides valuable insights into the molecular mechanisms involved in secondary xylem differentiation as well as new candidate-genes for wood quality improvement.