Phylogeny and expression of paralogous and orthologous sulphate transporter genes in diploid and hexaplold wheats

Twelve genes encoding two closely related subtypes (ST1.1a and ST1.1b) of a sulphate transporter have been identified in the diploid wheats Aegilops tauschii, Triticum urartu, and Aegilops speltoides, as well as the hexaploid Triticum aestivum. Based on phylogenetic comparisons with other plant sulphate transporters, the ST1.1a and 1.1b subtypes aligned with group I of the plant sulphate transporter gene family. The exon-intron structure was conserved within the ST1.1a or ST1.1b genes; however, substantial variability in intron sequences existed between the two types. The high overall sequence similarity indicated that ST1.1b represented a duplication of the ST1.1a gene, which must have occurred before the evolution of the ancestral diploid wheat progenitor. In contrast with the close relationship of the T urartu and Ae. tauschii sequences to the corresponding A and D genome sequences of T aestivum, the divergence between the Ae. speltoides sequences and the B genome sequences suggested that the B genome ST1.1a gene has been modified by recombination. Transcript analysis revealed predominant expression of the ST1.1a type and an influence of sulphur availability on the level of expression.