Distant hybridization serves as a crucial method for germplasm innovation and variety improvement in ornamental plants; however, hybridization barriers hinder the creation of new varieties. Michelia compressa (Maxim.) Sarg., an evergreen tree belonging to the Magnolia (Magnoliaceae), is highly regarded for its exceptional ornamental qualities and resilience. In the case of intergeneric hybridization in M. compressa, pre-fertilization barriers complicate the acquisition of hybrid progeny, although the specific mechanisms underlying this phenomenon remain unclear. This study employed metabolomics, single-molecule real-time sequencing technology, and Illumina RNA sequencing to identify key metabolites and regulatory genes responsible for the observed affinity differences in interspecific and intergeneric hybridization of M. compressa. Functional validation was conducted on the key gene pectin methylesterase (PME), specifically the McoPME4 gene. Results indicated that double fertilization was successfully completed in interspecific hybridization at 4 days after pollination, while intergeneric hybridization faced challenges in achieving the same within the same timeframe. Metabolomic analysis of the M. compressa gynoecium following pollination revealed 1520 differentially accumulated metabolites. Furthermore, transcriptomic analysis identified 901 differentially expressed genes. Multi-omics analysis confirmed McoPME4 as a pivotal gene contributing to the interspecific hybridization in M. compressa × Michelia maudiae. The validation through genetic engineering demonstrated that the use of antisense oligonucleotides targeting McoPME4 significantly inhibited pollen tube growth. Conversely, the prokaryotic expression of McoPME4 was found to accelerate the growth rates of pollen tubes. Notably, in the Arabidopsis thaliana phenotype that overexpresses McoPME4, a marked enhancement in fertility was observed. In summary, these findings offer valuable insights into the mechanisms underlying the barriers to intergeneric hybridization in M. compressa.
Cui et al. (Wed,) studied this question.