Transcriptome Analysis of Apricot Kernel Pistils Reveals the Mechanisms Underlying ROS-Mediated Freezing Resistance

Abstract

Spring frost is a major limiting factor in the production and cultivation of apricot kernels, an ecological and economic dry-fruit tree in China. The frequent occurrence of spring frost often coincides with the blooming period of apricot kernels, resulting in significant damage to floral organs and reductions in yield. We investigated the molecular signature of pistils from two apricot kernel cultivars with different frost-resistance levels using transcriptome data. A total of 3223 differently expressed genes (DEGs) were found between two apricot kernel cultivars under freezing stress, including the bHLH and AP2/ERF-ERF transcription factors. Based on KEGG analysis, DEGs were mostly enriched in the biosynthesis of the secondary metabolites, in the metabolic pathways, and in plant-hormone signal transduction. The co-expression network, which included 81 hub genes, revealed that transcription factors, protein kinases, ubiquitin ligases, hormone components, and Ca2+-related proteins coregulated the ROS-mediated freezing response. Moreover, gene interaction relationships, such as ERF109-HMGCR1, ERF109-GRXC9, and bHLH13-JAZ8, were predicted. These findings revealed the regulatory factors for differences in frost resistance between the two tested apricot kernel cultivars and contributed to a deeper understanding of the comprehensive regulatory program during freezing stress. Some of the hub genes identified in this work provide new choices and directions for breeding apricot kernels with a high frost resistance.