Identification and Analysis of Aluminum-Activated Malate Transporter Gene Family Reveals Functional Diversification in Orchidaceae and the Expression Patterns of Aluminum-Activated Malate Transporters.

Aluminum-activated malate transporter () genes play an important role in aluminum ion (Al) tolerance, fruit acidity, and stomatal movement. Although decades of research have been carried out in many plants, there is little knowledge about the roles of in Orchidaceae. In this study, 34 genes were identified in the genomes of four orchid species. Specifically, ten genes were found in and , and seven were found in and . These genes were further categorized into four clades (clades 1-4) based on phylogenetic relationships. Sequence alignment and conserved motif analysis revealed that most orchid proteins contain conserved regions (TM1, GABA binding motif, and WEP motif). We also discovered a unique motif (19) belonging to clade 1, which can serve as a specifically identified characteristic. Comparison with the gene structure of genes () showed that the gene structure of was conserved across species, but the introns were longer in orchids. The promoters of orchid genes contain many light-responsive and hormone-responsive elements, suggesting that their expression may be regulated by light and phytohormones. Chromosomal localization and collinear analysis of indicated that tandem duplication (TD) is the main reason for the difference in the number of genes in these orchids. was chosen for the RT-qPCR experiment, and the results showed that the gene expression pattern varied in different tissues. The expression of was significantly changed after ABA treatment. Combining the circadian CO uptake rate, titratable total acid, and RT-qPCR data analysis, most genes were highly expressed at night and around dawn. The result revealed that genes might be involved in photosynthate accumulation. The above study provides more comprehensive information for the gene family in Orchidaceae and a basis for subsequent functional analysis.