Pyrophosphate-dependent phosphofructokinase (PFP) catalyses the reversible phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate in the glycolysis pathway. Two full-length complementary DNAs encoding putative PFP α- and β-subunits, named EjPFPa and EjPFPb1, were isolated by reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of the cDNA ends (RACE) from Eriobotrya japonica Lindl. (loquat). The other β-subunit gene was identified from transcriptome data obtained by Illumina sequencing, designated as EjPFPb2. They share up to 88 % identity with other plant PFP α/β-subunits. EjPFPa and EjPFPb clustered separately in clades of plant PFP α- or β-subunits, respectively. EjPFPa and EjPFPb were both shown to be mainly localised in the cell membrane using confocal microscopy of GFP fusion proteins 35S:EjPFPa/b-GFP. Monitoring the dynamic changes of transcripts and proteins demonstrated that EjPFPa and EjPFPb did not show coordinated expression during fruit development in loquat. The transcript levels of EjPFPa and EjPFPb in the leaves of loquat seedlings were significantly enhanced after 3 h of treatment with 0.5, 1.0 and 1.5 M fructose or glucose, which indicates that EjPFPa and EjPFPb are modulated by fructose and glucose in vivo. Transgenic tobacco plants overexpressed EjPFPa did not show visible phenotype changes, while plants overexpressing EjPFPb1 grew faster at the cost of reduced leaf size and sucrose content. Meanwhile, fructose content increased in growing plants compared with wild-type plants. The results confirm that genes of the two subunits from loquat PFP have different transcriptional regulation systems and play different roles in carbohydrate metabolism. Elevation of the PFP β-subunit gene expression can partly impact the glycolytic carbon allocation in growing plants.

Sugar and acid content and sugar/acid ratio are the important indexes for fruit quality.Sugars not only determine fruit sweetness,but also provide raw materials for synthesis of pigment,amino acids,vitamins and other nutrients and aromatic substances.Fruit acids and sugar form sugar/acid ratio,which decides fruit flavor.Meanwhile,fruit organic acids provide respiratory substrates for the synthesis of other essential substances.Sugar/acid ratio is one of the most important determiner for fruit quality.Sugar and organic acid metabolism processes are extremely complicated,the two pathways are closely connected.Understanding towards sugar and acid accumulation mechanism would provide important theoretical basis for cultivation and breeding.This article reviews the recent research advances on loquat(Eriobotrya japonica) sugar acid metabolism,physiology,molecular biology,and cultivation,etc,which will be helpful for related areas.Combining the authors’ research experience,the possible researching focuses on future loquat sugar and acid metabolic and regulation mechanism are proposed: further clarify the molecular mechanism of cultivation measures and environment factors on the fruit sugar and acid metabolism;ascertain the fruit sugar and acid transporting mechanisms;regulate fruit sugar and acid composition by genetic engineering technology;clarify the interaction mechanism of sugar accumulation and acid accumulation.

分析了浙江省3个杨梅主栽品种东魁、荸荠、晚稻果实糖、有机酸的种类和含量。结果表明,供试3个杨梅品种果实糖含量及组分差异较大,晚稻果实蔗糖含量最高,而荸荠果实葡萄糖和果糖含量最高;3个杨梅品种果实均以苹果酸含量最高,其次是琥珀酸和柠檬酸;果实可溶性固形物含量荸荠显著高于东魁、晚稻,可滴定酸含量东魁果实最高,其次为荸荠、晚稻;糖酸比:晚稻>荸荠>东魁,且品种间差异均达显著水平。