Inducible expression by plant hormones of S-adenosyl- l-homocysteine hydrolase gene from Nicotiana tabacum during early flower bud formation in vitro

Abstract

cDNA clones corresponding to genes induced during the early stage of flower bud formation in thin cell layer (TCL) cultures of tobacco were isolated by differential screening. Sequence analysis showed that one of the clones encoded S-adenosyl- l-homocysteine hydrolase (SAHH), which is known to be an enzyme regulating intracellular transmethylation reactions. Recently, it was also found to be a cytokinin-binding protein. An SAHH gene was isolated by screening a tobacco genomic library with the cDNA as a probe. Northern blot analysis showed that expression of the SAHH gene was greatest in pistils and roots, and could be induced by kinetin and IAA. Kinetin and IAA are required for in vitro flower differentiation in TCL culture. The promoter sequence of the gene was fused to the β-glucuronidase (GUS) reporter gene and introduced in suspension-cultured cells, which rendered expression of GUS inducible by kinetin. Possible involvement of SAHH in regulation of gene expression, cytokinin signal transduction and flower differentiation is discussed.