Summary• Here, orthologous genes of six phosphate transporter (PiT) genes, which are members of the Pht1 and Pht2 families in tomato and potato, have been cloned from the solanaceous species pepper, eggplant and tobacco.• Overall, expressions of these genes in pepper, eggplant and tobacco showed similar patterns to those in tomato and potato: P-starvation enhancement in both leaves and roots for Pht1;1 , P-depletion induction exclusively in roots for Pht1;2 , mycorrhizal enhancement for Pht1;3 , and mycorrhizal induction for both Pht1;4 and Pht1;5 .• In the roots of nonmycorrhizal eggplant, SmPht1;3 , SmPht1;4 and SmPht1;5 were also expressed under extreme P starvation. Mycorrhizal symbiosis under high-P supply conditions reduced plant growth, with concurrent enhancement of Pht1;2 expression in the roots of pepper as well as eggplant. In addition, the mycorrhizal symbiosis down-regulated the expression of Pht2;1 genes greatly in the leaves of pepper and tobacco.• The discrepancies between the evolutionary distances of the PiT genes and their expression patterns among the five species suggest greater complexity in function of PiT in plants than previously expected.

Summary• In this study, six putative promoter regions of phosphate transporter Pht1;3, Pht1;4 and Pht1;5 genes were isolated from eggplant and tobacco using the inverse polymerase chain reaction (iPCR). The isolated sequences show evolutionary conservation and divergence within ⁄ between the two groups of Pht1;3 and Pht1;4 ⁄ Pht1;5.• Histochemical analyses showed that all six promoter fragments were sufficient to drive b-glucuronidase (GUS) expression specifically in arbuscular mycorrhizal (AM) tobacco roots and were confined to distinct cells containing AM fungal structures (arbuscules or intracellular hyphae).• A series of promoter truncation and mutation analyses combined with phylogenetic footprinting of these promoters revealed that at least two cis-regulatory elements -the mycorrhiza transcription factor binding sequence (MYCS) first identified in this study and P1BS -mediated the transcriptional activation of the AM-mediated inorganic phosphate (Pi) transporter genes. Deletion or partial mutation of either of the two motifs in the promoters could cause a remarkable decrease, or even complete absence, of the promoter activity.• Our results propose that uptake of inorganic phosphate (Pi) by AM fungi is regulated, at least partially, in an MYCS-and P1BS-dependent manner in eudicot species. Our finding offers new insights into the molecular mechanisms underlying the coordination between the AM and the Pi signalling pathways.

BackgroundIn plants, sucrose synthase (Sus) is widely considered as a key enzyme involved in sucrose metabolism. Several paralogous genes encoding different isozymes of Sus have been identified and characterized in multiple plant genomes, while limited information of Sus genes is available to date for cotton.ResultsHere, we report the molecular cloning, structural organization, phylogenetic evolution and expression profiles of seven Sus genes (GaSus1 to 7) identified from diploid fiber cotton (Gossypium arboreum). Comparisons between cDNA and genomic sequences revealed that the cotton GaSus genes were interrupted by multiple introns. Comparative screening of introns in homologous genes demonstrated that the number and position of Sus introns are highly conserved among Sus genes in cotton and other more distantly related plant species. Phylogenetic analysis showed that GaSus1, GaSus2, GaSus3, GaSus4 and GaSus5 could be clustered together into a dicot Sus group, while GaSus6 and GaSus7 were separated evenly into other two groups, with members from both dicot and monocot species. Expression profiles analyses of the seven Sus genes indicated that except GaSus2, of which the transcripts was undetectable in all tissues examined, and GaSus7, which was only expressed in stem and petal, the other five paralogues were differentially expressed in a wide ranges of tissues, and showed development-dependent expression profiles in cotton fiber cells.ConclusionsThis is a comprehensive study of the Sus gene family in cotton plant. The results presented in this work provide new insights into the evolutionary conservation and sub-functional divergence of the cotton Sus gene family in response to cotton fiber growth and development.

BackgroundPhosphorus (P) deficiency is one of the major nutrient stresses limiting plant growth. The uptake of P by plants is well considered to be mediated by a number of high-affinity phosphate (Pi) transporters belonging to the Pht1 family. Although the Pht1 genes have been extensively identified in several plant species, there is a lack of systematic analysis of the Pht1 gene family in any solanaceous species thus far.ResultsHere, we report the genome-wide analysis, phylogenetic evolution and expression patterns of the Pht1 genes in tomato (Solanum lycopersicum). A total of eight putative Pht1 genes (LePT1 to 8), distributed on three chromosomes (3, 6 and 9), were identified through extensive searches of the released tomato genome sequence database. Chromosomal organization and phylogenetic tree analysis suggested that the six Pht1 paralogues, LePT1/3, LePT2/6 and LePT4/5, which were assigned into three pairs with very close physical distance, were produced from recent tandem duplication events that occurred after Solanaceae splitting with other dicot families. Expression analysis of these Pht1 members revealed that except LePT8, of which the transcript was undetectable in all tissues, the other seven paralogues showed differential but partial-overlapping expression patterns. LePT1 and LePT7 were ubiquitously expressed in all tissues examined, and their transcripts were induced abundantly in response to Pi starvation; LePT2 and LePT6, the two paralogues harboring identical coding sequence, were predominantly expressed in Pi-deficient roots; LePT3, LePT4 and LePT5 were strongly activated in the roots colonized by arbuscular mycorrhizal fungi under low-P, but not high-P condition. Histochemical analysis revealed that a 1250-bp LePT3 promoter fragment and a 471-bp LePT5 promoter fragment containing the two elements, MYCS and P1BS, were sufficient to direct the GUS reporter expression in mycorrhizal roots and were limited to distinct cells harboring AM fungal structures. Additionally, the four paralogues, LePT1, LePT2, LePT6 and LePT7, were very significantly down-regulated in the mycorrhizal roots under low Pi supply condition.ConclusionsThe results obtained from this study provide new insights into the evolutionary expansion, functional divergence and genetic redundancy of the Pht1 genes in response to Pi deficiency and mycorrhizal symbiosis in tomato.