Os01g0919400

OsSPS1 is a gene encoding sucrose phosphate synthase(SPS) and is a menber of the sucrose phosphate synthase gene family in rice(OsSPSs).

Annotated Information

Function

• OsSPS1 is a gene encoding sucrose phosphate synthase(SPS). SPS catalyzes the conversion of fructose 6-phosphate and UDPglucose into sucrose 6-phosphate, and it is generally considered to be the rate-limiting enzyme in sucrose synthesis. OsSPS1 is one of the 5 isogenes encoding SPS in the rice genome and and plays a dominant role in sucrose synthesis among them.

• The suppression of OsSPS1 shortens the plant length of rice seedlings, and the locus of OsSPS1 appears to coincide with the quantitative trait locus(QTL)for plant height.

• Sucrose synthesis via OsSPS1 is essential in pollen germination in rice.

Mutation

File:SPS-M1

Figure 1. SPS activity of Koshihikari and NIL-SPS1 during the transplanting, panicle formation, heading, and mid-ripening stages.

• An NIL of rice (O. sativa L.) was generated in the process of developing chromosome segment substitution lines (CSSLs). The NIL-SPS1 carries a chromosome segment containing OsSPS1 of Kasalath on chromosome 1 in the genetic background of Koshihikari. Figure 1 shows the SPS enzyme activities in the source leaf blades of Koshihikari and NIL-SPS1 at different developmental stages. The SPS activity in NIL-SPS1 was 30% and 59% higher than that in Koshihikari at the transplanting and panicle formation stages, respectively. However, at later developmental stages, the SPS activity in NIL-SPS1 leaves did not differ significantly from that of Koshihikari.The plant height of NIL-SPS1 tended to be higher than that of Koshihikari throughout the measurement period, particularly after heading (Figure 2A). In contrast, tiller number in NIL-SPS1 tended to be lower than that in Koshihikari, but the difference was not significant(Figure 2B).

• A chemically inducible gene expression system was used on OsSPS1. Inducible gene suppression works with an RNAi cassette and this cassette targets OsSPS1. The inducer is β-estradiol. The seeds of the transgenic plants were sown on the MS agar plates containing 30 μM of β-estradiol and grown for a week. In two of the three independent transgenic lines that were examined, the transcript levels of OsSPS1 in the leaf blades of the β-estradiol-treated plants were significantly less than the levels in the control plants (Fig. 3A). Concomitantly, the shoot length of the β -estradiol-treated plants was shorter than that of the control plants (Fig. 3B). In another experiment, the induced seedlings were transplanted into plastic pots filled with soil and were further grown for four weeks. During this period, 100 μM of β-estradiol containing 0.02% Tween-20 was sprayed onto the terrestrial portions of the plant parts every week (three times in total). Again, the OsSPS1 mRNA levels in the leaf blades decreased significantly in two of the three transgenic lines (Fig. 4A). In the leaf blades of the induced plants, the molar ratio of sucrose to starch decreased significantly when compared to the uninduced control plants (Fig. 4B).

File:SPS-M6

Figure 1. SPS activity of Koshihikari and NIL-SPS1 during the transplanting, panicle formation, heading, and mid-ripening stages.

File:SPS-M7

Figure 1. SPS activity of Koshihikari and NIL-SPS1 during the transplanting, panicle formation, heading, and mid-ripening stages.

Expression Pattern

Figure 1. Diurnal patterns of the promoter activities of OsSPS1 under light/dark cycles .

• Expression analysis revealed that OsSPS1 is preferentially expressed in the source tissue, particularly in leaf blades, and it plays a dominant role in sucrose synthesis in the source leaf blades among the 5 isogenes for SPS.

• The promoter activities of sucrose phosphate synthase gene in rice, OsSPS1, is controlled by light and circadian clock, but not by sucrose. The promoter activities of OsSPS1 is low during the dark period and increased rapidly after the onset of the light period. While the promoter activity of OsSPS1 decreased gradually during the day and remained low through out the night(Figure2A).

Knowledge Extension

• Sucrose phosphate synthase(SPS,EC2.3.1.14)catalyzes the conversion of fructose-6-phosphate and UDP-glucose into sucrose-6-phosphate and isknown to be the major rate-limiting enzyme insucrose biosynthesis in plants.
• plant SPS genes are clustered into four groups(groupsA,B,C, andD),based on their amino acid sequences. Rice has five SPS genes, OsSPSs, classified into four groups: OsSPS8, OsSPS1, OsSPS11, and OsSPS2 and OsSPS6 in groupsA,B,C,andD,respectively.

Labs working on this gene

• Bio ResearchLaboratory,ToyotaMotorCorporation,Toyota,Aichi,Japan
• LaboratoryofCropScience,GraduateSchoolofAgriculturalandLifeSciences,TheUniversityofTokyo,Bunkyo-ku,Tokyo,Japan
• NAROAgriculturalResearchCenter,Joetsu,Niigata,Japan
• Center forGeneResearch,NagoyaUniversity,Chikusa-ku,Nagoya,Japan
• Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
• Toyama Prefectural Agricultural, Forestry & Fisheries Research Center, Toyama, Toyama 939-8153, Japan
• NARO Agricultural Research Center, Joetsu, Niigata 943-0193, Japan