Molecular Mechanisms of Heterosis and Its Applications in Tree Breeding: Progress and Perspectives

Heterosis, or hybrid vigor, refers to the phenomenon where hybrid progenies outperform their parents in traits such as yield and resistance. This phenomenon has been widely applied in plant breeding. Recent advances in high-throughput genomics have significantly advanced our understanding of heterosis. This review systematically summarizes the genetic, molecular, and epigenetic mechanisms underlying heterosis. Furthermore, we discuss recent advances in predictive methods for heterosis and their applications in improving growth rate, resistance to abiotic stresses, and wood yield in tree species. We also explore the role of tree genomics in unraveling the mechanisms underlying heterosis, emphasizing the potential of integrating high-resolution genomics, single-cell sequencing, and spatial transcriptomics to achieve a comprehensive understanding of heterosis from the molecular to spatial levels. Building on this, CRISPR-based gene-editing technologies can be employed to precisely edit heterotic loci, enabling the study of allele function. Additionally, molecular marker-assisted selection (MAS) can be utilized to identify heterotic loci in parental lines, facilitating the selection of optimal hybrid combinations and significantly reducing the labor and time costs of hybrid breeding. Finally, we review the utilization of heterosis in tree breeding and provide a forward-looking perspective on future research directions, highlighting the potential of integrating multi-omics approaches and emerging gene-editing tools to revolutionize tree hybrid breeding.