Abstract
Although sucrose plays a role in sugar sensing and its signaling pathway, little is known about the regulatory mechanisms of the expressions of plant sucrose-related genes. Our previous study on the expression of the sucrose phosphate synthase gene family in rice (OsSPSs) suggested the involvement of sucrose sensing and/or circadian rhythm in the transcriptional regulation of OsSPS. To examine whether the promoters of OsSPSs can be controlled by sugars and circadian clock, we produced transgenic rice plants harboring a promoter–luciferase construct for OsSPS1 or OsSPS11 and analyzed the changes in the promoter activities by monitoring bioluminescence from intact transgenic plants in real-time. Transgenic plants fed sucrose, glucose, or mannitol under continuous light conditions showed no changes in bioluminescence intensity; meanwhile, the addition of sucrose increased the concentration of sucrose in the plants, and the mRNA levels of OsSPS remained constant. These results suggest that these OsSPS promoters may not be regulated by sucrose levels in the tissues. Next, we investigated the changes in the promoter activities under 12-h light/12-h dark cycles and continuous light conditions. Under the light–dark cycle, both OsSPS1 and OsSPS11 promoter activities were low in the dark and increased rapidly after the beginning of the light period. When the transgenic rice plants were moved to the continuous light condition, both POsSPS1::LUC and POsSPS11::LUC reporter plants exhibited circadian bioluminescence rhythms; bioluminescence peaked during the subjective day with a 27-h period: in the early morning as for OsSPS1 promoter and midday for OsSPS11 promoter. These results indicate that these OsSPS promoters are controlled by both light illumination and circadian clock and that the regulatory mechanism of promoter activity differs between the two OsSPS genes.
Highlights
Sucrose is the major photosynthetic product and plays a central role in plant metabolism
We performed promoter–reporter assays for OsSPS1 and OsSPS11 in vivo using an automated bioluminescencemonitoring apparatus to investigate the potential regulation of the promoter activities of OsSPSs by sugars and/or circadian clock
To examine whether the promoter activities of OsSPS1 and OsSPS11 are regulated by sugars, we measured the bioluminescence of the promoter–luciferase reporter for OsSPS1 or OsSPS11 (POsSPS1)::LUC and POsSPS11::LUC reporter plants after exogenously supplying 5% (w/v) sucrose, 5% (w/v) glucose, or 5% (w/v) mannitol
Summary
Sucrose is the major photosynthetic product and plays a central role in plant metabolism. Sucrose is reported to be a signal molecule that regulates gene expression in plants (Chiou and Bush, 1998; Vaughn et al, 2002; Ransom-Hodgkins et al, 2003). Sucrose phosphate synthase (SPS, EC 2.3.1.14) catalyzes the conversion of fructose-6-phosphate and UDP-glucose into sucrose-6-phosphate and is known to be the major rate-limiting enzyme in sucrose biosynthesis in plants (Winter and Huber, 2000; Lunn and MacRae, 2003). Light–dark modulation of SPS activity via reversible phosphorylation is well established in several plant species (see Winter and Huber, 2000, for review). The expression of SPS genes can be regulated by light and cold stress at the transcriptional level (Chávez-Bárcenas et al, 2000; Lutfiyya et al, 2007; Okamura et al, 2011)
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