Transcriptome and metabolic changes reveal carotenoid biosynthetic metabolism during mesocarp and seed development of avocado (Persea americana)

Avocado (Persea americana Mill.) is considered as an important tropical and subtropical crop with high economic and nutritional value. However, the absence of the transcriptome of avocado hampers the investigation of the association of secondary metabolic mechanism. In this study, we obtained 365,615,152/348,623,402 clean reads and 109.13/104.10 Gb from the avocado mesocarp and seed, respectively, during five developmental stages. Moreover, comparing alpha- and beta-carotene contents in the mesocarp and seed during five developmental stages revealed tissue-specific accumulation, and alpha- and beta-carotene contents in the mesocarp were significantly higher than those in the seed. The high-quality reads were assembled into 100,837 unigenes with an average length of 847.40 bp (N50 = 1,725 bp). Besides, a total of 16,903 differentially expressed genes were identified at five fruit development stages, and 17 of these differentially expressed genes were found to be involved in carotenoid biosynthesis. Most of these 17 DEGs were up-regulated in the avocado mesocarp compared with those in the seed during five developmental stages. In the carotenoid pathway DEGs, the expression patterns of seven carotenoid biosynthetic genes including PaPSY (c103350.graph_c0 and c113873.graph_c5), PaZ-ISO (c109620.graph_c1), PaCRTISO (c108133.graph_c1), PaLCY-E (c117627.graph_c3), and PaLCY-B (c92930.graph_c0 and c110018.graph_c0) could play important roles in promoting the synthesis of alpha- and beta-carotene in avocado mesocarp. These results will help to further understand the carotenoid biosynthesis in avocado.