Gibberellin Biosynthesis in Plants and Fungi: A Case of Convergent Evolution?

Abstract

As well as being phytohormones, gibberellins (GAs) are present in some fungi and bacteria. Indeed, GAs were first discovered in the fungus Gibberella fujikuroi, from which gibberellic acid (GA3) and other GAs are produced commercially. Although higher plants and the fungus produce structurally identical GAs, there are important differences in the pathways and enzymes involved. This has become particularly apparent with the identification of almost all of the genes for GA-biosynthesis in Arabidopsis thaliana and G. fujikuroi, following the sequencing of the Arabidopsis genome and the detection of a GA-biosynthesis gene cluster in the fungus. For example, 3b-hydroxylation occurs early in the pathway in G. fujikuroi and is catalyzed by a cytochrome P450 monooxygenase, whereas it is usually the final step in plants and is catalyzed by 2-oxoglutarate-dependent dioxygenases. Similarly, 20-oxidation is catalyzed by dioxygenases in plants and a cytochrome P450 in the fungus. Even where cytochrome P450s have equivalent functions in plants and Gibberella, they are unrelated in terms of amino acid sequence. These profound differences indicate that higher plants and fungi have evolved their complex biosynthetic pathways to GAs independently and not by horizontal gene transfer.

Cloning and Overproduction of Gibberellin 3-Oxidase in Hybrid Aspen Trees. Effects on Gibberellin Homeostasis and Development

“…5). In Arabidopsis, GA20ox and GA3ox are both encoded by at least four genes (Hedden et al, 2001), so the possibility that the expression of other gene family members is negatively affected in the transgenic lines cannot be excluded. Because both PttGA20ox1 and PttGA3ox1 have been shown to be feedback regulated by bioactive GAs (Eriksson and Moritz, 2002;M.…”

“…The existence of four Populus GA3ox genes was confirmed by BLAST searches of PttGA3ox1 in the ongoing Populus trichocarpa genome sequencing program (http://genome.jgi-psf.org/poplar0/ poplar0.home.html; data not shown). In comparison, GA3ox in Arabidopsis is encoded by four genes, and their functions have been confirmed by heterologous expression in E. coli (Hedden et al, 2001). …”

“…The genes encoding the three described enzymes have been cloned in several species and have been found to belong to small multigene families. In Arabidopsis there are at least four genes coding for each enzyme (Hedden et al, 2001).Maintaining the levels of the bioactive GAs in appropriate temporal and spatial patterns, while controlling the responsiveness of each tissue to GAs, are vital processes for the plant during its growth and development. Recent studies in Arabidopsis, rice (Oryza sativa), and barley (Hordeum vulgare) have identified several positive and negative regulators of GA signaling pathways, all involved in regulating GA responsiveness during development (for review, see Olszewski et al, 2002;Gomi and Matsuoka, 2003).…”

“…The genes encoding the three described enzymes have been cloned in several species and have been found to belong to small multigene families. In Arabidopsis there are at least four genes coding for each enzyme (Hedden et al, 2001).…”

Evolution of growth-promoting plant hormones

“…In fungi (Hedden et al 2002) and the moss P. patens (Hayashi et al 2006), a single bifunctional enzyme catalyses the two steps involved in converting geranylgeranyl diphosphate to ent-kaurene (Davidson et al 2006). In contrast, in the angiosperms, there is a separate monofunctional enzyme for each step (Davidson et al 2006).…”