Integrated microRNA and transcriptome profiling reveals the regulatory network of embryo abortion in jujube.

Hybridization is an important approach to the production of new varieties with exceptional traits. Although the kernel rate of wild jujube (Z. jujuba Mill. var. spinosa Hu.) is generally high, that of cultivated jujube (Ziziphus jujuba Mill.) is low, greatly hampering the jujube breeding process. However, the mechanism by which this trait changed during jujube domestication remains unclear. Here, we explored the potential regulatory network that governs jujube embryo abortion using correlation analysis of population traits, artificial pollination, sugar content measurements, and multi-omics analysis. The results showed that embryo abortion was an important reason for the low kernel rate of cultivated jujube, and kernel rate was negatively correlated with edible rate. Twenty-one days after pollination was a critical period for embryo abortion. At this time, the sugar content of cultivated 'Junzao' kernels decreased significantly compared with that of the pulp, but sugar content remained relatively stable in kernels of wild 'Suanzao'. A total of 1,142 differentially expressed genes targeted by 93 miRNAs were identified by transcriptome, miRNA, and degradome sequencing and may be involved in the regulation of embryo abortion during kernel development. Among them, DELLA protein, TCP14, and bHLH93 transcription factors have been shown to participate in the regulation of embryonic development. Our findings suggest that carbohydrate flow between different tissues of cultivated jujube exhibits a bias toward the pulp at 21 days after pollination, thereby restricting the process of kernel development. This information enhances our understanding of the embryo abortion process and reveals miRNA-target gene pairs that may be useful for molecular-assisted breeding.