RNA-Seq analysis to investigate alternate bearing mechanism in Pistacia vera L

Pistachio (Pistacia vera L.) production suffers a high level of alternate bearing. The mechanism underlying this negative phenomenon is different from other species, such as apple and olive. Pistachio produces a high number of inflorescence buds every year that in heavy cropping trees (“ON”) mostly fall during the kernel development phase, which occurs in July-August. Primary metabolites (i.e., carbohydrates) play a key role in the signaling related to inflorescence bud abscission. In this work, RNA-Seq was used as a tool to investigate transcriptome of inflorescence buds and fruits, sampled from branches with low (“OFF”) and high (“ON”) crop load. Reference based RNA-Seq analysis using Arabidopsis thaliana genome was performed to discover differentially regulated genes in “ON” vs. “OFF” branches. In fruits developed on “ON” branches, photosynthesis, terpenoid and alpha-amylase-related genes were induced while tetrapyrrole was repressed; in inflorescence buds, photosynthesis was repressed while two genes involved in terpenoids pathways were still induced in comparison to the buds bore on “OFF” branches. A comparison with citrus transcriptomic data was performed. The data collected in the present study will be further utilized by the completion of pistachio genome and transcriptome de novo assembly.