Brassinosteroids (BRs) are growth-promoting natural products found at low levels in pollen, seeds, and young vegetative tissues throughout the plant kingdom. Detailed studies of BR biosynthesis and metabolism, coupled with the recent identification of BR-insensitive and BR-deficient mutants, has greatly expanded our view of steroids as signals controlling plant growth and development. This review examines the microchemical and molecular genetic analyses that have provided convincing evidence for an essential role of BRs in diverse developmental programs, including cell expansion, vascular differentiation, etiolation, and reproductive development. Recent advances relevant to the molecular mechanisms of BR-regulated gene expression and BR signal transduction are also discussed.

BRASSINOSTEROIDS: Essential Regulators of Plant Growth and Development

https://www.mpipz.mpg.de/25701/Szekeres_Cell_85.pdf

Brassinosteroids Rescue the Deficiency of CYP90, a Cytochrome P450, Controlling Cell Elongation and De-etiolation in Arabidopsis

Extracts of Brassica napus L. (rape) pollen (family, Cruciferae) have been reported to produce a novel growth-promoting effect when applied to young pinto bean plants1,2. Fractions that are active in the bean second-internode assay3 give rise to both increased cell elongation and cell division4. The validity of these early reports has been questioned because biological activity was not correlated with any one pure compound5. Subsequently, we showed that isolation of the growth promoter was complicated by the presence of chromatographically similar, inactive components that were identified as 6-D-glucopyranosyl esters of long-chain fatty acids6. We now report the isolation, structure determination and biological activity of this new plant growth promoter, named (22R, 23R, 24S)-2α-3α,22,23-tetrahydroxy-24-methyl-6,7-s-5α-cholestano-6,7-lactone or brassinolide (Fig. 1).

Brassinolide, a plant growth-promoting steroid isolated from Brassica napus pollen

Brassinosteroids are widely distributed plant compounds that modulate cell elongation and division, but little is known about the mechanism of action of these plant growth regulators. To investigate brassinosteroids as signals influencing plant growth and development, we identified a brassinosteroid-insensitive mutant in Arabidopsis thaliana (L.) Henyh. ecotype Columbia. The mutant, termed bri1, did not respond to brassinosteroids in hypocotyl elongation and primary root inhibition assays, but it did retain sensitivity to auxins, cytokinins, ethylene, abscisic acid, and gibberellins. The bri1 mutant showed multiple deficiencies in developmental pathways that could not be rescued by brassinosteroid treatment including a severely dwarfed stature; dark green, thickened leaves; males sterility; reduced apical dominance; and de-etiolation of dark-grown seedlings. Genetic analysis suggests that the Bri1 phenotype is caused by a recessive mutation in a single gene with pleiotropic effects that maps 1.6 centimorgans from the cleaved, amplified, polymorphic sequence marker DHS1 on the bottom of chromosome IV. The multiple and dramatic effects of mutation of the BRI1 locus on development suggests that the BRI1 gene may play a critical role in brassinosteroid perception or signal transduction.

A Brassinosteroid-Insensitive Mutant in Arabidopsis thaliana Exhibits Multiple Defects in Growth and Development

Brassinosteroids (BRs) are plant growth–promoting natural products required for plant growth and development. Physiological studies have demonstrated that exogenous BR, alone or in combination with auxin, enhance bending of the lamina joint of rice. However, little is known about the function of endogenous BR in rice or other grass species. We report here the phenotypical and molecular characterization of a rice dwarf mutant, d61, that is less sensitive to BR compared to the wild type. We cloned a rice gene, OsBRI1, with extensive sequence similarity to that of the Arabidopsis BRI gene, which encodes a putative BR receptor kinase. Linkage analysis showed that the OsBRI1 gene is closely linked to the d61 locus. Single nucleotide substitutions found at different sites of the d61 alleles would give rise to amino acid changes in the corresponding polypeptides. Furthermore, introduction of the entire OsBRI1 coding region, including the 5′ and 3′ flanking sequences, into d61 plants complemented the mutation to display the wild-type phenotype. Transgenic plants carrying the antisense strand of the OsBRI1 transcript showed similar or even more severe phenotypes than those of the d61 mutants. Our results show that OsBRI1 functions in various growth and developmental processes in rice, including (1) internode elongation, by inducing the formation of the intercalary meristem and the longitudinal elongation of internode cells; (2) bending of the lamina joint; and (3) skotomorphogenesis.

/pdf/loss-of-function-of-a-rice-brassinosteroid-insensitive1-pl4ij8kszm.pdf

Michael D. Grove

Papers

Brassinolide, a plant growth-promoting steroid isolated from Brassica napus pollen

Morphine and codeine in poppy seed.

Detection of brassinolide and castasterone in Alnus glutinosa (European alder) pollen by mass spectrometry/mass spectrometry

Ammoniation products of an aflatoxin model coumarin

6-D-glucopyranosyl fatty acid esters from Brassica napus pollen