Details

Autor(en) / Beteiligte

• Legge, Duncan James

Titel

The role and regulation of sugar transporters in Arabidopsis

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2004

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Sugar transporters are essential for assimilate partitioning and cellular nutrition, and their activities must be carefully controlled to meet the demands of plant growth and development under changing environmental conditions. Analysis of the Arabidopsis genome, in this and other studies, has revealed that there are large, multi-gene families of sugar transporters. The next challenge is to determine their individual physiological function. This thesis describes a number of different approaches to understand the role of sugar transporters in Arabidopsis thaliana. Insertion mutants from the Sainsbury Laboratory Arabidopsis d Spm. Transposant (SLAT) collection were used to investigate the function of the sucrose transporters AtSUC1 and AtSUC2. Phenotypic analyses of these mutants demonstrate that AtSUC1 and AtSUC2 have substantially different roles in growth and development of Arabidopsis. The suc1-1 mutant was similar to wild-type (WT) plants in terms of general growth and development. In contrast, knocking out AtSUC2 had severe effects at all developmental stages. The suc2 mutants were severely retarded in their growth and, at maturity, were significantly smaller in height with fewer and smaller leaves and a reduced number of flowers. Siliques developed in some cases, but these were generally shorter in length and produced significantly smaller seed than in WT plants. Importantly, although previously isolated suc2 mutants were reported as sterile, those isolated in this study could produce viable seed although viability varied between individual plants. Exogenously supplied sucrose did not fully rescue the suc2 mutant phenotype. An alternative approach to understanding gene function is to investigate the regulation of gene expression. This was undertaken for representative genes from two important sugar transporter families, the disaccharide transporter, AtSUC2, and the monosaccharide transporter, AtSTP4. Gene expression was investigated in Arabidopsis seedlings using RT-PCR and reporter gene technology concentrating on two potential regulators of sugar transporter gene expression, sugar availability and light. Both activate signalling pathways in plants and sugar transporters may be targets for regulation by these stimuli. Experiments using transgenic Arabidopsis plants containing promoter: GUS fusions demonstrated that AtSUC2 and AtSTP4 were both expressed in all organs with AtSUC2 expression concentrated in the vascular tissue. Neither AtSUC2 nor AtSTP4 expression was dramatically different in light- and dark-grown seedlings. However, both genes were repressed by exogenous sucrose with AtSUC2 inhibited more than 50% by just 10 mM sucrose, but not markedly affected by glucose, fructose or mannitol. AtSTP4 was much less sensitive to sucrose than AtSUC2. A more global approach to understanding light regulation of sugar transporter expression was taken by utilising microarray technology with a custom-made Arabidopsis membrane transporter array containing oligonucleotides representing all sugar transporter genes. This transcriptomics approach identified several transporters showing changes in gene expression in response to far-red light, which specifically activates phytochrome A. These results will provide a starting point for further targeted analysis of the role of sugar transporters in light-regulated seedling development.