Gibberellins Inhibit Flavonoid Biosynthesis and Promote Nitrogen Metabolism in Medicago truncatula

Abstract

Bioactive gibberellic acids (GAs) are diterpenoid plant hormones that are biosynthesized through complex pathways and control various aspects of growth and development. Although GA biosynthesis has been intensively studied, the downstream metabolic pathways regulated by GAs have remained largely unexplored. We investigated Tnt1 retrotransposon insertion mutant lines of Medicago truncatula with a dwarf phenotype by forward and reverse genetics screening and phylogenetic, molecular, biochemical, proteomic and metabolomic analyses. Three Tnt1 retrotransposon insertion mutant lines of the gibberellin 3-beta-dioxygenase 1 gene (GA3ox1) with a dwarf phenotype were identified, in which the synthesis of GAs (GA3 and GA4) was inhibited. Phenotypic analysis revealed that plant height, root and petiole length of ga3ox1 mutants were shorter than those of the wild type (Medicago truncatula ecotype R108). Leaf size was also much smaller in ga3ox1 mutants than that in wild-type R108, which is probably due to cell-size diminution instead of a decrease in cell number. Proteomic and metabolomic analyses of ga3ox1/R108 leaves revealed that in the ga3ox1 mutant, flavonoid isoflavonoid biosynthesis was significantly up-regulated, while nitrogen metabolism was down-regulated. Additionally, we further demonstrated that flavonoid and isoflavonoid biosynthesis was induced by prohexadione calcium, an inhibitor of GA3ox enzyme, and inhibited by exogenous GA3. In contrast, nitrogen metabolism was promoted by exogenous GA3 but inhibited by prohexadione calcium. The results of this study further demonstrated that GAs play critical roles in positively regulating nitrogen metabolism and transport and negatively regulating flavonoid biosynthesis through GA-mediated signaling pathways in leaves.

Environmental Stimuli and Phytohormones in Anthocyanin Biosynthesis: A Comprehensive Review

“…Moreover, studies also showed that the GA-DELLA module is involved in nitrogen-deficiency-induced anthocyanin accumulation. DELLAs could interact with PAP1 and enhance the transcriptional activity of PAP1 to promote the expressions of F3 H and DFR [37,101].…”

Effects of tree age on flavonoids and antioxidant activity in Torreya grandis nuts via integrated metabolome and transcriptome analyses

“…Treatment with ABA results in a higher accumulation of total anthocyanin via increasing the expression of VvCHI and VvF3H in grape (Koyama et al., 2018). In Medicago truncatula , GA inhibits the biosynthesis of flavonoid and isoflavonoid via regulating the transcripts of flavonoid biosynthesis genes, such as MtCHI , MtCHS , and MtDFR (Sun et al., 2021). Future work needs to unravel the mechanism by which ABA and GA affect the age‐related flavonoid accumulation.…”

Different Responses of Invasive Weed Alternanthera philoxeroides and Oryza sativa to Plant Growth Regulators

“…Endogenous GA is extremely important when encountering biotic or abiotic stress. Endogenous GA reduction might increase flavonoid content in plants [ 46 ] and contribute to improving plant ability to resist stress [ 47 ]. Therefore, the chlorophyll and leaf nitrogen increasing due to PAC application might affect plant resistance to abiotic or biotic stress.…”