Genome-wide investigation and expression analysis suggest diverse roles and genetic redundancy of Pht1 family genes in response to Pi deficiency in tomato

Abstract

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.

Insights On the Impact of Arbuscular Mycorrhizal Symbiosis On Tomato Tolerance to Water Stress

“…Gene expression data were calculated as expression ratios (relative quantity) to control NS plants. Gene-specific primers are listed in Supplemental Table S1 (Corrado et al, 2007;Weiss and Egea-Cortines, 2009;González-Guerrero et al, 2010;López-Ráez et al, 2010;Li et al, 2013b;Chen et al, 2014). In all experiments, the transcript level of the arbuscular mycorrhiza-inducible phosphate transporter LePT4 was evaluated as a marker for mycorrhizal functionality, showing a typical expression profile with an overexpression trend in the presence of both the AM fungi, in both WS and NS conditions, with respect to control NS plants (data not shown).…”

A Functional Approach towards Understanding the Role of the Mitochondrial Respiratory Chain in an Endomycorrhizal Symbiosis

“…The expression of six ( StPT1, 2/6, 3, 4, 5 , and 8 ) out of the ten previously described PT genes belonging to the Pht1 family in S. tuberosum (Leggewie et al, 1997; Rausch et al, 2001; Nagy et al, 2005; Chen et al, 2014) was studied. The expression of StPT2 and StPT6 was not dissociable and was considered as a sum StPT2/6 .…”

“…StPT8, StPT9 , and StPT10 were all located in the same region of the chromosome 9. The expression of StPT8 , which shares the highest homology with SlPT7 (Chen et al, 2014), was studied. In R. irregulare , the Pht1 family was divided into four different clusters named after the S. cerevisiae sequences therein (Supplementary Figure S4).…”

Comprehensive Genomic Identification and Expression Analysis of the Phosphate Transporter (PHT) Gene Family in Apple

“…Eight of the nine PHT1 family genes in Arabidopsis are expressed in the roots (Bucher et al, 2001; Mudge et al, 2002). By comparison, eight PHT1 genes in tomato (Chen et al, 2014) and 10 of the 13 PHT1 genes in rice are expressed in the roots (Paszkowski et al, 2002). We also detected MdPHT1;1, MdPHT1;2, MdPHT1;7, MdPHT1;13 , and MdPHT1;14 transcripts in both leaves and roots.…”