Differential Expression Analysis of Reference Genes in Pineapple ( Ananas comosus L.) during Reproductive Development and Response to Abiotic Stress, Hormonal Stimuli

Pineapple ( Ananas comosus L.), a popular tropical fruit, is a good model for evolutionary analysis and genetic research on adaptation to drought habitats, multiple fruits, and crassulacean acid metabolism (CAM) photosynthesis. Reliable reference genes for the normalization of the levels of development-related and/or stress-responsive genes is important for elucidating the mechanisms of plant development as well as their adaptation to various environments. In this study, ten candidate reference genes were selected, and the expression stability of each gene was assessed across 105 pineapple samples, consisting of different reproductive organs (stigma, petal, sepal, ovule, anther, flower, and fruitlet), abiotic stress (salinity, drought, and cold), and hormones (abscisic acid, ethylene, jasmonic acid, and salicylic acid). Our results revealed that PP2A and UBQ were stably expressed during pineapple reproductive development. PP2A and CYC were the stable reference genes across abiotic stress, whereas RAN and EF1α / PP2A was the best candidates for various hormones. To validate the feasibility of using these stably expressed genes for further experiments, we evaluated the expression profile of AcMYB30 across different samples. Our results provide important insights on the growth and development of the pineapple plant as well as information on stress-tolerance genes and stress-signaling pathways in this important fruit.