Regulation of the gibberellin biosynthetic gene GA1 in Arabidopsis thaliana.

摘要

Plant hormone gibberellins (GAs) control many aspects of plant growth and developmental processes including seed germination, stem elongation, flower induction and fruit development. Genetic and physiological studies have provided much evidence that GAs are signals to modulate plant growth in response to both environmental stimuli and endogenous developmental programs. In Arabidopsis thaliana, the GA1 gene encodes copalyl diphosphate synthase that catalyzes the first committed step in the GA biosynthetic pathway. The expression of the GA1 gene is regulated in a cell-type-specific manner. Investigation of mechanisms regulating GA1 gene expression was carried out through dissection of the GA1 promoter and genetic screening for trans-acting mutants defective in GA1 gene expression. For promoter deletion analyses, a series of GA1-β-glucuronidase( GUS) constructs with various degrees of deletion either from 5 ′ or 3′ end of the full-length GA1 promoter were introduced into Arabidopsis. Several cis -regulatory regions controlling GA1 gene expression were identified. The first two introns act to increase GA1 gene expression. The region between −1391 and −997 relative to the GA1 translational start site positively regulates the overall expression of the GA1-GUS transgene. One seed-specific positive regulatory region is located between −997 and −796. In addition, a positive regulatory region between −425 and −207 and a negative regulatory region between −18A8 and −1391 controlled GA1-GUS expression in many tissues but not in seed. 12 putative mutants were isolated from an ethylmethane sulfonate-mutagenized M₂ population based on altered expression pattern of the GA1-GUS gene in flowers and siliques. Further analyses indicated that decreased GA1-GUS activities in several plants isolated were caused by gene silencing. Discrepancies between the expression levels of the endogenous GA1 gene and the GA1-GUS transgene were observed in the mutants with ectopic and increased GUS activities. One mutant with enhanced GA1-GUS expression level but reduced endogenous GA1 expression level in developing seeds was selected for further characterization. Genetic analyses indicated that a single gene mutation caused parent-of origin-dependent phenotypes including enhanced GA1-GUS gene expression in seed and aberrant seed development. The mutated locus was located within a 91-kb region in the lower portion of Chromosome 2.