Table 1. Comparison of relative mRNA expression for genes encoding enzymes involved in sugar metabolism (including MdSDHs, MdCWINVs, MdNINVs, MdvAINVs, MdSUSYs, MdFKs, MdHKs, and MdSPSs) among mature leaves, shoot tips, young fruit (40 DAB) and mature fruit (135 DAB) of apple.

	MdSDH1	MdSDH2-9	MdCWINV1	MdCWINV2	MdCWINV3	MdNINV1	MdNINV2
Mature leaves	1.00±0.33	1.00±0.25	1.00±0.18	1.00±0.26	1.00±0.23	1.00±0.19	1.00±0.18
Shoot tips	0.50±0.08	6.01±0.75	0.85±0.22	3.31±0.37	3.34±0.21	0.40±0.07	1.64±0.34
Young fruit	2.10±0.44	81.7±7.08	n/d	0.69±0.08	3.22±0.09	1.04±0.06	1.53±0.11
Mature fruit	17.6±2.01	49.2±6.83	0.03±0.01	0.06±0.01	0.02±0.01	0.60±0.13	0.73±0.12

Values are means of three technical replicates of the reverse transcribed RNA sample pooled from 5 biological replicates ± SD. n/d means no expression was detected.

qRT-PCR was performed with gene-specific primers, except that a pair of universal primers was designed from the conserved cDNA region of MdSDH2 to MdSDH9 for the expression of MdSDH2-9. For each sample, transcript levels were normalized with those of Actin, and the relative expression levels of each gene were obtained using the ddCT method while expression in mature leaves was designated as ‘1’.