Molecular Mechanism of Leaf Color Change in Air Plant (Tillandsia brachycaulos)

Air plant (Tillandsia spp.) is a unique epiphytic genus, and its diverse leaf colors constitute one of its main ornamental values. Anthocyanins are known to be major pigments contributing to leaf coloration in air plants, but the molecular mechanisms regulating their accumulation during leaf color change remain unclear. In this study, leaves at three different growth periods were selected, and transcriptome sequencing combined with high-performance liquid chromatography (HPLC) was used to quantify anthocyanins. Our results showed that soluble sugars, proteins, and the activities of superoxide dismutase (SOD) and peroxidase (POD) significantly increased, while total chlorophyll content decreased during three periods. Furthermore, transcriptome sequencing analysis identified 1782 differentially expressed genes (DEGs) shared by both comparisons (CL0 vs. CL1 and CL0 vs. CL2). Within the flavonoid and anthocyanin biosynthesis pathways, key genes such as F3H, F3′H, F3′5′H, DFR, ANS, arGST, UGT, UFGT and HCT were notably upregulated. Among the 102 transcription factors that exhibited significant differences, the expression patterns of eight MYB genes related to anthocyanin differ across the CL0, CL1, and CL2 stages. Among them, three MYB genes showed increased expression in CL1 and CL2 compared with CL0, whereas five other MYB genes showed the highest expression in CL0. Additionally, a total of 55 metabolites were detected, including nine anthocyanins whose changes in accumulation were associated with the leaf color transition. By integrating transcriptomic and targeted metabolomic approaches, this study identified the transcriptional and metabolic changes related to leaf coloration and conveyed candidate genes and MYB transcription potentially involved in anthocyanins in air plant. These findings provide candidate genes and a theoretical foundation for further understanding the mechanisms of anthocyanin accumulation in air plants and for future functional studies.