Characterization of uniconazole-induced dwarfism in banana
To confirm the effect of uniconazole on dwarfism in bananas, we designed a concentration gradient (0.1 g, 0.3 g, and 0.5 g) and compared the induced traits (Fig. 1). The plants in the control group exhibited a height of approximately 220 cm with normal banana stalks (Fig. 1A), and plants dwarfed to approximately 170 cm when treated with 0.1 g uniconazole (Fig. 1B). Treatment with 0.3 g uniconazole further dwarfed the plants to approximately 140 cm with short comb spacing (Fig. 1C), whereas an overdose of uniconazole (0.5 g) induced malformation of buds and a height of 135 cm (Fig. 1D).
Physiological and biochemical changes in uniconazole-induced dwarf banana
GA content was significantly downregulated in uniconazole-treated bananas. The lowest GA content was observed for both groups treated with 0.3 g and 0.5 g uniconazole (Fig. 2A). A considerable number of physiological and biochemical indices, including potassium, calcium, magnesium, phosphorus, soluble protein, and SOD activity, increased as the concentration gradient of uniconazole increased. In contrast, the levels of these indices in the control and paclobutrazol-treated groups were the lowest and highest, respectively (Fig. 2B-2I). In addition, the enzyme activities of CAT, PAL, and PPO showed a similar trend (Fig. 2J-2L). Consequently, the dosage of 0.3 g uniconazole was chosen for further metabolomic and transcriptomic experiments based on to the best dwarfism traits induced in banana and the minimum effect on physiological and biochemical indices.
Metabolomic changes associated with uniconazole-induced dwarfism
A total of 1,082 metabolites were identified based on the metabolomics data (Table S1), which showed a high correlation (r > 0.9) between replicates within groups (Fig. S1A). PCA showed clustering of samples into distinct groups and stages, and the treatment group was closer to the control group at 25 d than at 15 d (Fig. S1B).
A considerable number of differential metabolites (DAM) were identified between the treatment and control groups at 15 d (Fig. 3A). Among them, the levels of most differential flavonoids, tannins, and alkaloids increased after uniconazole induction, whereas those of most lipids, amino acids and derivatives, organic acids, nucleotides and derivatives, and terpenoids decreased (Fig. 3A). These DAM were significantly enriched in flavone and flavonol biosynthesis, betalain biosynthesis, flavonoid biosynthesis, isoquinoline alkaloid biosynthesis, thiamine metabolism, and phenylpropanoid biosynthesis pathways (Fig. 3B). Meanwhile, the levels of differential flavonoids and tannins also increased when treated with uniconazole at 25 d (Fig. 4A), and the differential metabolites participated in flavonoid biosynthesis, phenylpropanoid biosynthesis, and plant hormone signal transduction pathways (Fig. 4B). The common DAM between 15 d and 25 d showed a similar trend, including three downregulated (3'-adenylic acid, gentiopicroside, and lysoPC 18:4) and 19 upregulated metabolites, including mainly flavonoids (pinobanksin, epicatechin-epiafzelechin, apigenin-6-C-(2’-glucuronyl)xyloside, kaempferol-3,7-O-dirhamnoside (kaempferitrin), vitexin-2''-O-rhamnoside, pelargonidin-3-O-rutinoside, and catechin-catechin-catechin), and tannins (such as procyanidin, cinnamtannin, and arecatannin) (Table S2).
Global transcriptomic changes in response to uniconazole-induced dwarfism
After the removal of low-quality reads, a minimum of 40 million clean reads were obtained for each sample and mapped to the reference genome at a high mapping rate (> 91%) (Table S3). A high correlation (r ≥ 0.87) was observed between replicates within groups for transcriptomic data (Fig. S2A), and PCA analysis shows similar clusters with the metabolomics data (Figs.S1B and S2B).
DEG between the treatment and control groups at 15 d were identified (Fig. 5A), which are involved in photosynthesis and oxidative phosphorylation pathways (Fig. 5B) and associated with photosynthesis, response to cytokinin, xylem development, and phenylpropanoid biosynthetic process (Fig. 5C). DEG identified at 25 d (Fig. 6A) were enriched in protein processing in the endoplasmic reticulum, tyrosine metabolism, and isoquinoline alkaloid biosynthesis pathways (Fig. 6B) and associated with tyrosine metabolic process, fatty acid biosynthetic process, oxylipin biosynthetic process, suberin biosynthetic process, lipid oxidation, phenylpropanoid metabolic process, and peroxidase activity (Fig. 6C). No common DEG were observed between 15 d and 25 d.
Key pathways involved in uniconazole-induced dwarfism in banana
The common enriched pathways for both DEG and DAM between 15 d and 25 d were further examined, which included four key pathways: metabolic pathways, phenylpropanoid biosynthesis, flavonoid biosynthesis, and biosynthesis of secondary metabolites (Fig. 7A). Of these, the phenylpropanoid biosynthesis pathway comprises flavonoid biosynthesis. We further examined the differential factors in the phenylpropanoid biosynthesis pathway and found that the expression levels of shikimate O-hydroxycinnamoyltransferase (HCT) and the abundance of pinobanksin, vitexin, epigallocatechol, and peroxidase increased in uniconazole-treated bananas compared with the control group (Fig. 7B).