Analyses of the sucrose synthase gene family in cotton: structure, phylogeny and expression patterns

Here, 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.This 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.Sucrose is the major form of photosynthate for export from the source leaves into cellular metabolism of most plants [1]. The transfer of sucrose to the sink organs often requires its cleavage by two key enzymes: invertase (Inv), which hydrolyzes sucrose into glucose and fructose, and sucrose synthase (Sus), which is capable of catalyzing a reversible reaction but preferring to convert sucrose and UDP into fructose and UDP-glucose [2-4]. Both of the two enzymes have been demonstrated to be tightly linked with the processes of phloem unloading [5,6], and the Sus has also been well