Carbon partitioning and export in transgenic Arabidopsis thaliana with altered capacity for sucrose synthesis grown at low temperature: a role for metabolite transporters

Abstract

We investigated the role of metabolite transporters in cold acclimation by comparing the responses of wild-type (WT) Arabidopsis thaliana (Heynh.) with that of transgenic plants over-expressing sucrose-phosphate synthase (SPSox) or with that of antisense repression of cytosolic fructose-1,6-bisphosphatase (FBPas). Plants were grown at 23 ∞ C and then shifted to 5 ∞ C. We compared the leaves shifted to 5 ∞ C for 3 and 10 d with new leaves that developed at 5 ∞ C with control leaves on plants at 23 ∞ C. At 23 ∞ C, ectopic expression of SPS resulted in 30% more carbon being fixed per day and an increase in sucrose export from source leaves. This increase in fixation and export was supported by increased expression of the plastidic triose-phosphate transporter AtTPT and, to a lesser extent, the high-affinity Suc transporter AtSUC1. The improved photosynthetic performance of the SPSox plants was maintained after they were shifted to 5 ∞ C and this was associated with further increases in AtSUC1 expression but with a strong repression of AtTPT mRNA abundance. Similar responses were shown by WT plants during acclimation to low temperature and this response was attenuated in the low sucrose producing FBPas plants. These data suggest that a key element in recovering flux through carbohydrate metabolism in the cold is to control the partitioning of metabolites between the chloroplast and the cytosol, and Arabidopsis modulates the expression of AtTPT to maintain balanced carbon flow. Arabidopsis also up-regulates the expression of AtSUC1, and to lesser extent AtSUC2, as down-stream components facilitate sucrose transport in leaves that develop at low temperatures.

Transgenic alfalfa (Medicago sativa) with increased sucrose phosphate synthase activity shows enhanced growth when grown under N2-fixing conditions

“…These findings are consistent with other reports in the literature (Galtier et al 1995;Signora et al 1998;Ono et al 1999Ono et al , 2003Baxter et al 2003;Strand et al 2003;Lundmark et al 2006;Ramon et al 2008;Stitt et al 2010). The leaves of the transformants showed an intense bluish green color accompanied by an increase in chlorophyll (Chl) content with a more significant increase in Chl b level resulting in a significant drop in the Chl a:b ratio.…”

Analysis of Sugar Content and Expression of Sucrose Transporter Genes (<i>OsSUTs</i>) in Rice Tissues in Response to a Chilling Temperature

“…OsSUT2 is in the same SUT4 clade as Arabidopsis SUT4 (AtSUT4), the expression of which is regulated by sucrose levels (Lundmark et al 2006). The changes in expression of OsSUT2 in rice tissues appeared to be related to changes in sucrose content of the tissues induced by chilling treatment.…”

Changes in soluble carbohydrates in polar Caryophyllaceae and Poaceae plants in response to chilling

“…Carbon partitioning toward sucrose accumulation can be a result of both limitation of phloem export and inhibition of starch synthesis due to accumulation of phosphorylated intermediates (Usadel et al 2008). Sucrose biosynthesis at low temperature in the Arabidopsis plants over-expressing sucrose phosphate synthase reduced the inhibition of photosynthesis, maintained the mobilization of carbohydrates from source leaves to sinks and increased the rate at which freezing tolerance developed (Strand et al 2003;Lundmark et al 2006). Cold stress combined with high light intensity triggers photoinhibition of the chloroplast, affects integrity of plasma membrane (Sandve et al 2011) and ultrastructure of different organelles, especially chloroplasts (Kratsch and Wise 2000).…”