Genome-Wide Identification and Characterisation of the 4-Coumarate–CoA Ligase (4CL) Gene Family in Gastrodia elata and Their Transcriptional Response to Fungal Infection

Gastrodia elata Blume is an important medicinal orchid, yet its large-scale cultivation is increasingly threatened by fungal diseases. The 4-coumarate–CoA ligase (4CL) gene family directs a key step in phenylpropanoid metabolism and plant defence, but its composition and function in G. elata have not been investigated. We mined the G. elata genome for 4CL homologues, mapped their chromosomal locations, and analysed their gene structures, conserved motifs, phylogenetic relationships, promoter cis-elements and codon usage bias. Publicly available transcriptomes were used to examine tissue-specific expression and responses to fungal infection. Subcellular localisation of selected proteins was verified by transient expression in Arabidopsis protoplasts. Fourteen Ge4CL genes were identified and grouped into three clades. Two members, Ge4CL2 and Ge4CL5, were strongly upregulated in tubers challenged with fungal pathogens. Ge4CL2 localised to the nucleus, whereas Ge4CL5 localised to both the nucleus and the cytoplasm. Codon usage analysis suggested that Escherichia coli and Oryza sativa are suitable heterologous hosts for Ge4CL expression. This study provides the first genome-wide catalogue of 4CL genes in G. elata and suggests that Ge4CL2 and Ge4CL5 may participate in antifungal defence, although functional confirmation is still required. The dataset furnishes a foundation for functional characterisation and the molecular breeding of disease-resistant G. elata cultivars.