Effect of Brassinolide on Gene Expression in Elongating Soybean Epicotyls

Abstract

We have studied the effect of brassinolide (BR), a plant steroidal lactone, on the expression of auxin-regulated genes in soybean (Glycine max L. cv Williams 82) epicotyls. BR caused up to 4-fold increases in epicotyl length during extended assays at 10-M, in the absence of added auxin. Structurally related steroids failed to induce elongation or to alter the BR effect. Northern blot analysis, using sequences corresponding to auxin-regulated genes as probes, has shown that the molecular mechanism of BR-induced elongation is likely to differ from that of auxin-induced elongation in this system. BR does not rapidly induce members of the GH, SAUR, or ICW auxin-inducible gene families before the onset of elongation. BR enhances SAUR and GH1 transcripts after 18 h but has no effect on JCW1 or GH3 transcripts at any time examined. We have shown by two-dimensional gel analysis of in vitro translated mRNA that a submicromolar concentration of BR alters the pattern of gene expression in elongating soybean epicotyls.BR2, a plant growth-promoting steroidal lactone, is the most biologically active compound of a group of related natural products termed brassinosteroids (reviewed in ref. 13). BR elicits a broad spectrum of responses in plants including enhanced cell elongation (13) and division and differentiation (6), and a strong case recently has been made for brassinosteroids as a sixth class of endogenous plant growth regulators (25). Like auxin, BR has pronounced effects on the elongation of stem tissue. Maize mesocotyls, pea, Azuki bean, and mung bean epicotyls (9, 13, 30), bean and cucumber hypocotyls (12,14), and wheat coleoptiles (23) all respond to submicromolar concentrations of BR by elongating. It has been suggested that the effects of BR are mediated through auxin or that BR increases tissue sensitivity to endogenous auxins (13). Despite numerous physiological studies addressing BR-auxin interactions, there have been few studies reported in which molecular techniques were utilized to clarify the interaction of these growth regulators (6). '

BAS1 : A gene regulating brassinosteroid levels and light responsiveness in Arabidopsis

“…As is the case with BAS1, CYP450-mediated C26-hydroxylation inactivates the insect hormones ecdysteroids, although the precise enzyme has not been identified (36)(37)(38). Though ecdysteroids are inactivated in a similar manner to BRs, these insect hormones do not induce BR responses in plants (39). Other insect juvenile hormones can be hydroxylated and presumably catabolized in a similar manner to ecdysone (40).…”

Inhibition of Brassinosteroid Biosynthesis by Either a dwarf4 Mutation or a Brassinosteroid Biosynthesis Inhibitor Rescues Defects in Tropic Responses of Hypocotyls in the Arabidopsis Mutant nonphototropic hypocotyl 4

“…Although BR may affect hypocotyl bending through modulation of polar auxin transport, it has also been well established that auxin and BR interact at the transcriptional level (Clouse et al, 1992;Goda et al, 2002;Mü ssig et al, 2002;Yin et al, 2002). Seventeen to 25% of the auxin-induced genes are also activated by BL in microarray analyses (Goda et al, 2004;Nemhauser et al, 2004).…”

24-epibrassinolide regulated diminution of Cr metal toxicity in Brassica juncea L. plants

“…dicyclohexyl carbodiimide has revealed that elongation induced by BRs involve ATPases (Katsumi, 1985). Since other plant growth regulators such as GAs and auxins also promote cell elongation, the regulation of some auxin-regulated genes such as SAUR, GH1 and JCW was studied for response to BR (Clouse et al, 1992). This experiment showed that although GH1 and SAUR genes are upregulated by BR, the kinetics of regulation was very different when compared to their regulation by auxin.…”

“…They are highly effective in stimulating growth in young vegetative tissues. Brassinosteroids promoted elongation of mung bean, soybean, pea epicotyls, bean, sunflower and cucumber hypocotyls, Arabidopsis peduncles and Hordeum vulgare seedlings (Gregory, 1982;Clouse et al, 1992;Yu et al, 2004;Clouse, 2008 andKartal et al, 2009). Hypocotyl elongation of Packchoi (Brassica chinensis) by brassinosteroids was reported (Wang et al, 1993) and application to apical 3-mm region gave the best effect.…”