Expression level of PpsAPX using validated reference genes for normalization.

qRT-PCR data was normalized to the two most stable reference genes (SKD1 and YLS8), two commonly used reference genes (TUBβ and UBQ10), and two unstable genes (EF1a and MYB10). DP, flat-type trellis system, SP, spindle system. The numbers after DP and SP refer to the month.