Molecular Cloning and Characterization of Phenylalanine Ammonia-lyase and Cinnamate 4-Hydroxylase in the Phenylpropanoid Biosynthesis Pathway in Garlic (Allium sativum)

Superoxide dismutases (SODs) are key antioxidant enzymes that can detoxify the superoxide radicals generated by various stresses. Although various plant SODs have been suggested to improve stress tolerance, SODs in garlic, an economically important vegetable grown worldwide, remain relatively unknown. In this study, we found that heat stress strongly induced the activities of Cu/ZnSODs, FeSODs, and MnSODs in garlic leaves. In addition, we cloned four garlic SODs (AsSODs) and suggest that heat stress-increased SOD activity was reflected at least by the induction of these AsSODs. The results of the agro-infiltration assay suggested that the cloned AsSODs encoded functional SOD enzymes belonging to the Cu/ZnSOD and MnSOD families. As a first step toward understanding the enzymatic antioxidant system in garlic plants, our results provide a solid foundation for an in-depth analysis of the physiological functions of the AsSOD family.

Download Full-text

Glucosinolate and phenylpropanoid biosynthesis are linked by proteasome-dependent degradation of PAL

10.1101/668038 ◽

2019 ◽

Author(s):

Jeongim Kim ◽

Xuebin Zhang ◽

Pete Pascuzzi ◽

Chang-Jun Liu ◽

Clint Chapple

Keyword(s):

Transcriptional Regulation ◽

Secondary Metabolites ◽

Molecular Mechanism ◽

Environmental Conditions ◽

Phenylalanine Ammonia Lyase ◽

Dependent Manner ◽

Biosynthetic Pathways ◽

Biosynthesis Pathway ◽

Kelch Domain ◽

Phenylpropanoid Biosynthesis

Plants produce several hundreds of thousands of secondary metabolites that are important for adaptation to various environmental conditions. Although different groups of secondary metabolites are synthesized through unique biosynthetic pathways, plants must orchestrate their production simultaneously. Phenylpropanoids and glucosinolates are two classes of secondary metabolites that are synthesized through apparently independent biosynthetic pathways. Genetic evidence has revealed that the accumulation of glucosinolate intermediates limits phenylpropanoid production in a Mediator Subunit 5 (MED5) dependent manner. To elucidate the molecular mechanism underlying this process, we analyzed the transcriptomes of a suite of glucosinolate-deficient mutants using RNAseq and identified mis-regulated genes that are rescued by the disruption of MED5. The expression of a group of Kelch Domain F-Box genes (KFBs) that function in PAL degradation is affected in glucosinolate biosynthesis mutants and the disruption of these KFBs restores phenylpropanoid deficiency, dwarfism and sterility in the mutants. Our study suggests that glucosinolate/phenylpropanoid metabolic crosstalk involves the transcriptional regulation of KFB genes that initiate the degradation of the enzyme phenylalanine ammonia-lyase, which catalyzes the first step of the phenylpropanoid biosynthesis pathway. Nevertheless, KFB mutant plants remain partially sensitive to glucosinolate pathway mutations, suggesting that other mechanisms that link the two pathways also exist.

Download Full-text