Transcriptome and metabolite profiling analyses provide insight into volatile compounds of the apple cultivar 'Ruixue' and its parents during fruit development

Aroma is one the most crucial inherent quality attributes of fruit. Ruixue apples were selected from a cross between Pink Lady and Fuji, a later ripening yellow new cultivar.A total of 54 samples were subjected to transcriptome analyses.Total RNA was extracted from fruit of Ruixue, Pink Lady and Fuji at 120, 150, 170, 180, 190 and 200 DAFB using the CTAB method. RNA integrity was determined using 1.2% agarose gel electrophoresis. Quantitation of RNA was analysed using a NanoDrop ND1000 spectrophotometer (NanoDrop Technologies, Wilmington, DE, USA) and RNA quality was analysed with an Agilent Bioanalyzer 2100 system(Agilent Technologies, Palo Alto, CA, USA). mRNA (containing polA) was isolated from total RNA using magnetic beads with oligo (dT). Fifty-four cDNA libraries were constructed using the NEBNext UltraTM RNA Library Prep Kit for Illumina (NEB, USA) and sequenced on the Illumina HiSeq platform. To ensure the quality and reliability of transcriptome data analysis, low-quality reads and N-containing reads were removed from the raw RNA-seq reads.We identified a large number of aroma related genes involved in the fatty acid,isoleucine and sesquiterpenoid metabolism pathways and identified transcription factors that may regulate aroma biosynthesis. Our initial study facilitates a better understanding of the volatile aroma compounds that affect fruit flavour as well a the mechanisms underlying differences in flavour between Ruixue and its parents.