The DWF4 gene of Arabidopsis encodes a cytochrome P450 that mediates multiple 22alpha-hydroxylation steps in brassinosteroid biosynthesis

Overexpression of BnaAGL11, a MADS-Box Transcription Factor, Regulates Leaf Morphogenesis and Senescence in Brassica napus

Previous studies have reported that SEEDSTICK/AGAMOUS-LIKE 11 (AtSTK/AtAGL11), a MADS-box transcription factor, plays important roles in many biological processes in Arabidopsis thaliana. However, the function of BnaAGL11, an AtAGL11 homologous gene from Brassica napus, in leaf development remains unknown. Here, we found that the ectopic expression of any copy of Bna.C09.AGL11, Bna.A03.AGL11, and Bna.A09.AGL11 in A. thaliana led to smaller and curly leaves and promoted leaf senescence. Consistently, the overexpression of Bna.C09.AGL11 in B. napus also caused smaller and curly leaves and accelerated leaf senescence. Furthermore, we demonstrated that Bna.C09.AGL11 controlled leaf morphogenesis by indirectly downregulating the genes of Bna.A01.DWF4 and Bna.C07.PGX3 and promoted leaf senescence by indirectly upregulating the genes of Bna.A04.ABI5, Bna.A05.ABI5, Bna.C04.ABI5-1, and Bna.C01.SEN4 and directly activating the transcription of Bna.C04.ABI5-2 and Bna.C03.SEN4 genes. Our results provide new insights into the underlying regulatory mechanism of BnaAGL11 during leaf development in B. napus.

Comparative Transcriptome Analysis Identifies Genes Involved in Diosgenin Biosynthesis in Trigonella foenum-graecum L

Trigonella foenum-graecum L. (fenugreek) is a valuable resource of producing diosgenin which serves as a substrate for synthesizing more than two hundred kinds of steroidal drugs. Phytochemical analysis indicated that methyl jasmonate (MeJA) efficiently induced diosgenin biosynthesis in fenugreek seedlings. Though early steps up to cholesterol have recently been elucidated in plants, cytochrome P450 (CYP)- and glycosyltransferase (GT)-encoding genes involved in the late steps from cholesterol to diosgenin remain unknown. This study established comparative fenugreek transcriptome datasets from the MeJA-treated seedlings and the corresponding control lines. Differential gene expression analysis identified a number of MeJA-induced CYP and GT candidate genes. Further gene expression pattern analysis across a different MeJA-treating time points, together with a phylogenetic analysis, suggested specific family members of CYPs and GTs that may participate in the late steps during diosgenin biosynthesis. MeJA-induced transcription factors (TFs) that may play regulatory roles in diosgenin biosynthesis were also discussed. This study provided a valuable genetic resource to functionally characterize the genes involved in diosgenin biosynthesis, which will push forward the production of diosgenin in microbial organisms using a promising synthetic biology strategy.

Arabidopsis NAC Transcription Factor JUNGBRUNNEN1 Exerts Conserved Control Over Gibberellin and Brassinosteroid Metabolism and Signaling Genes in Tomato

The Arabidopsis thaliana NAC transcription factor JUNGBRUNNEN1 (AtJUB1) regulates growth by directly repressing GA3ox1 and DWF4, two key genes involved in gibberellin (GA) and brassinosteroid (BR) biosynthesis, respectively, leading to GA and BR deficiency phenotypes. AtJUB1 also reduces the expression of PIF4, a bHLH transcription factor that positively controls cell elongation, while it stimulates the expression of DELLA genes, which are important repressors of growth. Here, we extend our previous findings by demonstrating that AtJUB1 induces similar GA and BR deficiency phenotypes and changes in gene expression when overexpressed in tomato (Solanum lycopersicum). Importantly, and in accordance with the growth phenotypes observed, AtJUB1 inhibits the expression of growth-supporting genes, namely the tomato orthologs of GA3ox1, DWF4 and PIF4, but activates the expression of DELLA orthologs, by directly binding to their promoters. Overexpression of AtJUB1 in tomato delays fruit ripening, which is accompanied by reduced expression of several ripening-related genes, and leads to an increase in the levels of various amino acids (mostly proline, β-alanine, and phenylalanine), γ-aminobutyric acid (GABA), and major organic acids including glutamic acid and aspartic acid. The fact that AtJUB1 exerts an inhibitory effect on the GA/BR biosynthesis and PIF4 genes but acts as a direct activator of DELLA genes in both, Arabidopsis and tomato, strongly supports the model that the molecular constituents of the JUNGBRUNNEN1 growth control module are considerably conserved across species.

Analysis of the Metabolic Pathways Affected by Poly(γ-glutamic Acid) in Arabidopsis thaliana Based on GeneChip Microarray

Plant growth is promoted by poly(γ-glutamic acid) (γ-PGA). However, the molecular mechanism underlying such promotion is not yet well understood. Therefore, we used GeneChip microarrays to explore the effects of γ-PGA on gene transcription in Arabidopsis thaliana. Our results revealed 299 genes significantly regulated by γ-PGA. These differently expressed genes participate mainly in metabolic and cellular processes and in stimuli responses. The metabolic pathways linked to these differently expressed genes were also investigated. A total of 64 of the 299 differently expressed genes were shown to be directly involved in 24 pathways such as brassinosteroid biosynthesis, α-linolenic acid metabolism, phenylpropanoid biosynthesis, and nitrogen metabolism, all of which were influenced by γ-PGA. The analysis demonstrated that γ-PGA promoted nitrogen assimilation and biosynthesis of brassinosteroids, jasmonic acid, and lignins, providing a better explanation for why γ-PGA promotes growth and enhances stress tolerance in plants.

In vitro and in vivo evidence for the inhibition of brassinosteroid synthesis by propiconazole through interference with side chain hydroxylation

We carried out the biochemical evaluation of the target site of propiconazole in BR biosynthesis. Applying BR biosynthesis intermediates to Arabidopsis seedlings grown in the presence of propiconazole under dark condition, we found that the target site of propiconazole in BR biosynthesis can be identified among the C22 and C23 side chain hydroxylation steps from campestanol to teasterone. Using differential spectra techniques to determine the binding affinity of propiconazole to CYP90D1, which is responsible for C23 hydroxylation of BR, we found that propiconazole induced typical type II binding spectra in response to purified recombinant CYP90D1 and the Kd value was found approximately 0.76 μM.

Insights into the function and evolution of P450s in plant steroid metabolism

Numerous cytochrome P450 monooxygenases (P450s) have been known to be involved in the biosynthesis and metabolism of triterpenoids and steroids. This review will survey the oxidative reactions by such P450s and provide insights into the evolution of the steroid-biosynthetic P450 genes in the plant kingdom. Special emphasis is placed on brassinosteroids (BRs), plant steroid hormones, that play essential roles in the regulation of plant growth and development. Several P450s involved in BR biosynthesis and catabolism have recently been characterized by recombinant protein experiments, revealing a new route of the BR biosynthetic pathway.