Jie Yang

As core metabolites of the phenylpropane pathway, flavonoids and lignin compete for common metabolic flux, yet their regulatory crosstalk critically constrains resource partitioning between development and stress adaptation. In this review, we synthesise recent progress in mechanistic insights into flavonoid‐mediated regulation of seed dormancy and germination, vegetative growth, and reproductive growth, while clarifying lignin's role in reinforcing cell wall biomechanical integrity and establishing hydraulic conductivity conduits. We particularly focus on multi‐tiered regulatory networks through which these metabolites confer resilience to against biotic/abiotic stresses. We further establish flavonoid‐lignin homoeostasis as a pivotal regulator of growth‐defence trade‐offs and demonstrate that its precision engineering enables synergistic enhancement of plant vigour and stress adaptation. This study provides a molecular blueprint for developing high‐performance plants with balanced nutritional, stress‐tolerant, and ecological traits.

Pigeon pea is an important economic crop with medicinal and nutritional value. Unfortunately, pest infestation of leaves during postharvest storage seriously affects the quality of pigeon pea. Phytohormones play a crucial role in disease and pest defence by regulating the accumulation of specialized metabolites. Still, their impact on the postharvest storage of pigeon pea has not been reported. In this study, the physiological parameters and main phenotypes of pigeon pea leaves treated with MeJA, ABA, and GA were investigated for the first time. The activity of the antioxidant enzyme system, which eliminates reactive oxygen species, was enhanced by applying MeJA, GA, and ABA. MeJA, GA, and ABA significantly affected crown width, plant height, and relative water content in pigeon pea, respectively. Metabolomic profiling analysis identified phenolic compounds as the main differentially accumulated metabolites (DAMs). UPLC‐QqQ‐MS/MS identified stilbenes, flavanones, flavones, isoflavones and anthocyanins as major phenolic compounds responsive to MeJA, GA, and ABA induction. By feeding insects, it was found that the insects fed on MeJA‐, ABA‐, and GA‐treated leaves less than on control leaves. Correlation analysis confirmed that isoflavones play an important role in this process. Moreover, the expression of key genes involved in flavonoid biosynthetic pathways and anti‐insect‐related genes was regulated by MeJA, GA, and ABA. Overall, this work provides a new strategy for the cultivation and storage of pigeon pea or other commercial crops and preliminarily clarifies that flavonoid metabolites under plant hormone treatment can promote plant growth and defence against insects by regulating reactive oxygen species.

Main conclusion 226 CcCYP450 genes were identified at the genomic level and were classified into 45 clades based on phylogenetic analysis. CcCYP75B165 gene was found that might play important roles in the biosynthesis of flavonoids in pigeon pea, and was significantly induced by methyl jasmonate (MeJA). Abstract The cytochrome P450 mono-oxygenase (CYP450) superfamily plays a key role in the flavonoid biosynthesis pathway and resists different kinds of stresses. Several CYP450 genes have been identified to be involved in the biosynthesis of crop protection agents. However, the CcCYP450 genes from pigeon pea have not been identified. Here, 226 CcCYP450 genes were identified at the genomic level by analysing the gene structure, distribution on chromosomes, gene duplication, and conserved motifs and were classified into 45 clades based on phylogenetic analysis. RNA-seq analysis revealed clear details of CcCYP450 genes that varied with time of MeJA (methyl jasmonate) induction. Among them, six CcCYP450 subfamily genes were found that might play important roles in the biosynthesis of flavonoids in pigeon pea. The overexpression of CcCYP75B165 in pigeon pea significantly induced the accumulation of genistin and downregulated the contents of cajaninstilbene acid, apigenin, isovitexin, and genistein and the expression of flavonoid synthase genes. This study provides theoretical guidance and plant genetic resources for cultivating new pigeon pea varieties with high flavonoid contents and exploring the molecular mechanisms of the biosynthesis of flavonoids under MeJA treatment.

Main conclusion Thirty CcMYB were identified to involve in flavonoid and lignin biosynthesis in pigeon pea genome. A comprehensive analysis of gene structure, phylogenetic relationships, distribution on chromosomes, gene duplication, and expression patterns was performed. Abstract MYB transcription factor is one of the largest gene families in plants and plays critical roles in plant growth and development, as well as resistance to biotic and abiotic stress. However, the function of MYB genes in pigeon pea (Cajanus cajan) remains largely unknown. Here, 30 R2R3-MYB which involved flavonoid and lignin biosynthesis were identified in the pigeon pea genome and were classified into five groups based on phylogenetic analysis. Simultaneously, another 122 key enzyme genes from biosynthetic pathways of flavonoid and lignin were identified and all of them were mapped on 11 chromosomes with the co-linearity relationship. Among these genes, the intron/exon organization and motif compositions were conserved and they have undergone a strong purifying selection and tandem duplications during evolution. Expression profile analysis demonstrated most of these genes were expressed in different tissues and responded significantly to MeJA, RNA-seq analysis revealed clear details of genes varied with time of induction. Ten key genes from the phenylpropanoid pathway were selected to further verify whether they responded to induction under different abiotic stress conditions (UV-B, cold, heat, salt, drought, and GA₃). This study elaborates on potential regulatory relationships between R2R3-MYB genes and some key genes involved in flavonoid and lignin biosynthesis under MeJA treatment, as well as adding to the understanding of improving abiotic stress tolerance and regulating the secondary metabolism in woody crops. A simplified discussion model for the different regulation networks involved with flavonoid and lignin biosynthesis in pigeon pea is proposed.