Poster: Membrane Transport

Abs # 1239: Comparitive analysis of the Arabidopsis thaliana sucrose transporter gene family.

Presenter:	Bush, Daniel , dbush@uiuc.edu
Authors	Bush, Daniel  (A) (B)  Harrington, Gregory  (B)
Affiliations:	(A): Photosynthesis Research, USDA-ARS (B): Department of Plant Biology, UIUC

Plasma membrane sucrose transporters mediate key steps in phloem loading and unloading of photoassimilates in higher plants. The Arabidopsis thaliana genome contains either nine (Columbia and Wassilewskija) or eight (Landsber erecta) functional sucrose transporters. In Landsberg erecta AtSUT7 is an expressed pseudogene. To date, the products of five of these genes have been cloned (AtSUCs 1–5). These five genes are arrayed on three different chromosomes, with AtSUCs 1 and5 being a tandem repeat separated by 2.5 kb. These five genes have diverse exon/intron patterns. With the exception of AtSUT2/AtSUC3, the final size of their open reading frame is very similar. All five transporters exhibit similar biochemical properties, with sucrose binding affinities vary between 0.5 and 11.5 mM and some variability in optimal pH. Despite the molecular and biochemical similarities of these five genes, they are differentially regulated at the cell, developmental and physiological levels. The predicted open reading frames of the remaining 4 members of this gene family (AtSUTs 6-9) are 87 % or more identical at the amino acid level. They share identical intron/exon patterns, indicating that they are probably the result of relatively recent duplication events. The predicted ORFs of these 4 genes code for proteins truncated immediately after the end of trans-membrane domain 12. Thus, they have no C-terminal cytoplasmic domain, a characteristic unique to this sub-group of sucrose transporters. We are employing a reverse genetics approach to understand the roles and regulation of individual sucrose transporter gene family members in Arabidopsis.