Genome-wide identification and function analysis of the sucrose phosphate synthase MdSPS gene family in apple

Sucrose phosphate synthase(SPS)is a rate-limiting enzyme that works in conjunction with sucrose-6-phosphate phosphatase(SPP)for sucrose synthesis,and it plays an essential role in energy provisioning during growth and development in plants as well as improving fruit quality.However,studies on the systematic analysis and evolutionary pattern of the SPS gene family in apple are still lacking.In the present study,a total of seven MdSPS and four MdSPP genes were identified from the Malus domestica genome GDDH13 v1.1.The gene structures and their promoter cis-elements,protein conserved motifs,subcellular localizations,physiological functions and biochemical properties were analyzed.A chromosomal location and gene-duplication analysis demonstrated that whole-genome duplication(WGD)and segmental duplication played vital roles in MdSPS gene family expansion.The Ka/Ks ratio of pairwise MdSPS genes indicated that the members of this family have undergone strong purifying selection during domestication.Furthermore,three SPS gene subfamilies were classified based on phylogenetic relationships,and old gene duplications and significantly divergent evolutionary rates were observed among the SPS gene subfamilies.In addition,a major gene related to sucrose accumulation(MdSPSA2.3)was identified according to the highly consistent trends in the changes of its expression in four apple varieties(‘Golden Delicious’,‘Fuji’,‘Qinguan’and‘Honeycrisp’)and the correlation between gene expression and soluble sugar content during fruit development.Furthermore,the virus-induced silencing of MdSPSA2.3 confirmed its function in sucrose accumulation in apple fruit.The present study lays a theoretical foundation for better clarifying the biological functions of the MdSPS genes during apple fruit development.

Polyphosphate Accelerates Transformation of Nonstructural Carbohydrates to Improve Growth of ppk-Expressing Transgenic Rice in Phosphorus Deficiency Culture

Crop yield and quality are often limited by the amount of phosphate fertilizer added to infertile soils,a key limiting factor for sustainable development in modern agriculture.The polyphosphate kinase(ppk)gene-expressing transgenic rice with a single-copy line(ETRS)is constructed to improve phosphate fertilizer utilization efficiency for phosphorus resource conservation.To investigate the potential mechanisms of the increased biomass in ETRS in low phosphate culture,ETRS was cultivated in a low inorganic phosphate(Pi)culture medium(15μmol/L Pi,LP)and a normal Pi culture medium(300μmol/L Pi,CP),respectively.After 89 d of cultivation in different concentrations of phosphate culture media,the total phosphorus,polyphosphate(polyP),biomass,photosynthetic rate,nonstructural carbohydrate(NSC)contents,related enzyme activities,and related gene expression levels were analyzed.The results showed that ETRS had a high polyP amount to promote the photosynthetic rate in LP,and its biomass was almost the same as the wild type(WT)in CP.The NSC content of ETRS in LP was higher than that of WT in LP,but slightly lower than that of WT in CP.PolyP notably promoted the sucrose phosphate synthase activities of ETRS and significantly down-regulated the expression levels of sucrose transporter genes(OsSUT3 and OsSUT4),resulting in inhibiting the transport of sucrose from shoot to root in ETRS.It was concluded that polyP can stimulate the synthesis of NSCs in LP,which improved the growth of ETRS and triggered the biological activities of ETRS to save phosphate fertilizer.Our study provides a new way to improve the utilization rate of phosphate fertilizer in rice production.

Transformation of Sucrose to Starch and Protein in Rice Leaves and Grains under Two Establishment Methods

Six rice varieties, PR120, PR116, Feng Ai Zan, PR115, PAU201 and Punjab Mehak 1 were raised under aerobic and transplanting conditions to assess the effects of planting conditions on sucrose metabolising enzymes in relation to the transformation of free sugars to starch and protein in flag leaves and grains. Activities of sucrose synthase, sucrose phosphate synthase and acid invertase increased till flowering stage in leaves and mid-milky stage（14 d after flowering） in grains and thereafter declined in concomitant with the contents of reducing sugar. Under aerobic conditions, the activities of acid invertase and sucrose synthase（cleavage） significantly decreased in conjunction with the decrease in non-reducing sugars and starch content in all the varieties. Disruption of starch biosynthesis under the influence of aerobic conditions in both leaves and grains and the higher build up of sugars possibly resulted in their favoured utilization in nitrogen metabolism. Feng Ai Zan, PR115 and PR120 maintained higher levels of sucrose synthase enzymes in grains and leaves and contents of metabolites（amino acid, protein and non-reducing sugar） under aerobic conditions, while PR116, Punjab Mehak 1 and PAU201 performed better under transplanting conditions, thus showing their adaptation to environmental stress. Yield gap between aerobic and transplanting rice is attributed primarily to the difference in sink activity and strength. Overall, it appear that up-regulation of sucrose synthase（synthesis） and sucrose phosphate synthase under aerobic conditions might be responsible in enhancing growth and productivity of rice varieties.

Alterations in sucrose metabolizing enzyme activities and total phenol content of Curcuma longa L. as affected by different triazole compounds

Changes in the sucrose metabolism of Cur-cuma longa L.plants were studied under treatment with different triazole compounds viz.,triadimefon(TDM)and propiconazole(PCZ).Plants were treated with TDM at 15mg/L and PCZ at 10mg/L separately by soil drenching on 80,110,and 140 days after planting(DAP).The plants were harvested randomly on 90,120,and 150DAP to determine the effect of both the triazoles on sucrose metabolizing enzymes and phenol content.The sucrose metabolism was studied by analyzing sucrose metaboliz-ing enzymes like sucrose synthase and sucrose phosphate synthase.All the analyses were assayed in leaves and tubers of both control and treated plants.It was found that both of the triazole compounds had profound effects on these parameters.

AKINβ1 is Involved in the Regulation of Nitrogen Metabolism and Sugar Signaling in Arabidopsis

Sucrose non-fermenting-l-related protein kinase 1 （SnRK1） has been located at the heart of the control of metabolism and development in plants. The active SnRK1 form is usually a heterotrimeric complex. Subcellular localization and specific target of the SnRK1 kinase are regulated by specific beta subunits. In Arabidopsis, there are at least seven genes encoding beta subunits, of which the regulatory functions are not yet clear. Here, we tried to study the function of one beta subunit, AKINβ1. It showed that AKINβ1 expression was dramatically induced by ammonia nitrate but not potassium nitrate, and the investigation of AKINβ1 transgenic Arabidopsis and T-DNA insertion lines showed that AKINβ1 negatively regulated the activity of nitrate ruductase and was positively involved in sugar repression in early seedling development. Meanwhile AKIN/β1 expression was reduced upon sugar treatment （including mannitol） and did not affect the activity of sucrose phosphate synthase. The results indicate that AKIN/β1 is involved in the regulation of nitrogen metabolism and sugar signaling.