Apple Sucrose Transporter SUT1 and Sorbitol Transporter SOT6 Interact with Cytochromeb5to Regulate Their Affinity for Substrate Sugars    

Abstract

Sugar transporters are central machineries to mediate cross-membrane transport of sugars into the cells, and sugar availability may serve as a signal to regulate the sugar transporters. However, the mechanisms of sugar transport regulation by signal sugar availability remain unclear in plant and animal cells. Here, we report that a sucrose transporter, MdSUT1, and a sorbitol transporter, MdSOT6, both localized to plasma membrane, were identified from apple (Malus domestica) fruit. Using a combination of the split-ubiquitin yeast two-hybrid, immunocoprecipitation, and bimolecular fluorescence complementation assays, the two distinct sugar transporters were shown to interact physically with an apple endoplasmic reticulum-anchored cytochrome b5 MdCYB5 in vitro and in vivo. In the yeast systems, the two different interaction complexes function to upregulate the affinity of the sugar transporters, allowing cells to adapt to sugar starvation. An Arabidopsis (Arabidopsis thaliana) homolog of MdCYB5, AtCYB5-A, also interacts with the two sugar transporters and functions similarly. The point mutations leucine-73 / proline in MdSUT1 and leucine-117 / proline in MdSOT6, disrupting the bimolecular interactions but without significantly affecting the transporter activities, abolish the stimulating effects of the sugar transporter-cytochrome b5 complex on the affinity of the sugar transporters. However, the yeast (Saccharomyces cerevisiae) cytochrome b5 ScCYB5, an additional interacting partner of the two plant sugar transporters, has no function in the regulation of the sugar transporters, indicating that the observed biological functions in the yeast systems are specific to plant cytochrome b5s. These findings suggest a novel mechanism by which the plant cells tailor sugar uptake to the surrounding sugar availability.

Expression of Sucrose Transporter cDNAs Specifically in Companion Cells Enhances Phloem Loading and Long-Distance Transport of Sucrose but Leads to an Inhibition of Growth and the Perception of a Phosphate Limitation

“…Research presented here demonstrates that while AtSUC2p is repressed, CoYMVp is up-regulated in the presence of elevated Suc levels and thus can be used to bypass possible endogenous regulation of AtSUC2 expression at the transcriptional level. In addition to transcriptional regulation, there is evidence for posttranslational regulation of SUT activity through protein-protein interactions (Schulze et al, 2003;Krügel et al, 2008Krügel et al, , 2009Fan et al, 2009). To potentially bypass these levels of regulation, SUT genes from each of the four subfamily types (Reinders et al, 2012) were tested for the capacity to SUT OE lines perceive a P deficiency as indicated by rescue of wild-type (WT) levels of growth with P supplements and increased expression of PSI genes.…”

Sequences and transcriptional analysis ofCoffea arabicavar. Caturra andCoffea libericaplant responses to coffee berry borerHypothenemus hampei(Coleoptera: Curculionidae: Scolytinae) attack

“…Among the proteins that the literature reports to respond to general metabolism were found: a CR9 protein involved in plant growth and development by regulating cell cycle (Alfenas-Zerbini et al 2009), a succinate dehydrogenase related to mitochondrial respiration (Millar et al 2004) and cytochrome B5 implicated in sugar transportation interviewing with flowering and fruit development (Fan et al 2009).…”

Carbohydrate Export from the Leaf: A Highly Regulated Process and Target to Enhance Photosynthesis and Productivity

“…Recently, novel posttranslational regulation of Suc transporters was suggested from a study identifying interactions between cytochrome b 5 and Suc and sorbitol transporters (Fan et al, 2009). A split-ubiquitin system, coimmunoprecipitation, and bimolecular fluorescence were used to show that the apple (Malus domestica) Suc symporter MdSUT1 and the apple sorbitol transporter MdSOT6 both interact with the apple endoplasmic reticulum-localized cytochrome b 5 protein encoded by MdCYB5.…”