It seems that different genes regulate FT orthologues to elicit seasonal flowering-responses in arabidopsis and the cereals. This highlights the need for more detailed study into the molecular basis of seasonal flowering-responses in cereal crops or in closely related model plants such as Brachypodium distachyon.

We have shown that ent-kaurenoic acid oxidase, a member of the CYP88A subfamily of cytochrome P450 enzymes, catalyzes the three steps of the gibberellin biosynthetic pathway from entkaurenoic acid to GA 12. A gibberellin-responsive barley mutant, grd5, accumulates ent-kaurenoic acid in developing grains. Three independent grd5 mutants contain mutations in a gene encoding a member of the CYP88A subfamily of cytochrome P450 enzymes, defined by the maize Dwarf3 protein. Mutation of the Dwarf3 gene gives rise to a gibberellin-responsive dwarf phenotype, but the lesion in the gibberellin biosynthesis pathway has not been identified. Arabidopsis thaliana has two CYP88A genes, both of which are expressed. Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA 12. Sequence comparison suggests that the maize Dwarf3 locus also encodes ent-kaurenoic acid oxidase. G ibberellins (GAs) are an important class of plant hormone involved in the regulation of processes from seed germination through the development and reproduction of plants (1). GA biosynthesis is catalyzed by three classes of enzymes: terpene cyclases catalyze the synthesis of ent-kaurene from geranylgeranyl diphosphate; cytochrome P450 monooxygenases catalyze the steps of the pathway from ent-kaurene to GA 12 ; and soluble dioxygenases catalyze the final steps of the pathway.Genes encoding enzymes for the two terpene cyclasecatalyzed steps, copalyl diphosphate synthase and kaurene synthase, have been isolated from a number of species (2, 3). Similarly, a wide range of 2-oxoglutarate-dependent dioxygenases encoding GA 7-oxidase, GA 20-oxidase, GA 2␤, 3␤-hydroxylase, GA 3␤-hydroxylase, and GA 2-oxidase activities have been isolated (2,(4)(5)(6). GA3 from Arabidopsis thaliana is the only gene encoding a cytochrome P450-mediated step of GA biosynthesis isolated (7), although the maize Dwarf3 gene is likely also to be involved in GA biosynthesis, and it encodes a member of the CYP88A subfamily of cytochrome P450 enzymes (8). GA3 encodes the cytochrome P450 CYP701A3 (7) and has been shown to catalyze the three-step oxidation of ent-kaurene to ent-kaurenoic acid (KA) (9). In line with current nomenclature for GA biosynthesis enzymes and the corresponding genes (10), we will refer to GA3 as AtKO1. The genes encoding the enzymes catalyzing the conversion of KA to ent-7␣-hydroxykaurenoic acid (7OH-KA) and 7OH-KA to GA 12 -aldehyde have not been isolated, but it is known that these reactions are likely to be catalyzed by cytochrome P450s requiring O 2 and NADPH for activity (11).The maize Dwarf3 gene encodes the cytochrome P450 CYP88A1 (8). The dwarf3 mutant is a GA-responsive dwarf (12); however, the reaction catalyzed by CYP88A1 has not been defined (2). It is likely that Dwarf3 is a GA biosynthetic enzyme, and therefore it may catalyze one of the steps between KA and GA 12 . We have described the isolation of a cDNA-encoding CYP88A2 from pumpk...

Methylation of plant DNA occurs at cytosines in any sequence context, and as the Arabidopsis methyltransferase, METI, preferentially methylates cytosines in CG dinucleotides, it is likely that Arabidopsis has other methyltransferases with different target specificities. We have identified five additional genes encoding putative DNA methyltransferases. Three of these genes are very similar to METI throughout the coding region; these genes probably arose by a series of gene duplication events, the most recent giving rise to METIIa and METIIb. METIIa and b are expressed at low levels in vegetative and floral organs and the level of transcripts is not affected by the introduction of a METI antisense transgene, nor do the METII enzymes substitute for the reduced activity of METI in methylating CG dinucleotides. METIII is not essential as it encodes a truncated protein. Two other genes encode a second class of DNA methyltransferase with the conserved motifs characteristic of cytosine methyltransferases, but with little homology to the METI-like methyltransferases through the remainder of the protein. These two methyltransferases are characterized by the presence of a chromodomain inserted within the methyltransferase domain, suggesting that they may be associated with heterochromatin. Both these genes are transcribed at low levels in vegetative and reproductive tissues.