Effects of perturbing expression of the polyamine catabolic AtCuAO gene family on growth and development in Arabidopsis thaliana.

Polyamines (PAs) are involved in controlling cell division and elongation, somatic embryogenesis, plant growth, development and senescence. The most common PAs in plants are putrescine (Put), spermidine (Spd) and spermine (Spm). Their concentration in the cell is regulated by a balance between biosynthesis and catabolism. Catabolism occurs through oxidative de-amination of PAs, by the action of amine oxidase enzymes (AOs). In Arabidopsis, copper-containing di-amine oxidases, one of the two classes of AO enzymes in plants, form a gene family of ten members with different patterns of expression. We have taken two approaches to understanding their function. Firstly, we are examining in detail the effects of insertional mutants in each member of the gene family on levels of PAs and growth and development. We have shown a clear phenotypic response to perturbation of AtCuAO4 (At4g12290) expression. Mutation of this gene resulted in accumulation of Put in leaves before bolting, and increased Spm and Spd after bolting. Plant development, flowering and senescence were delayed in AtCuAO4 mutants. The delay in senescence was related to flowering time as there were no differences between lines in dark-induced senescence. Stalk height was also lower in the mutant lines, and was linked to GA levels. As a second approach we have transformed wild type Arabidopsis with artificial micro RNAs complementary to multiple AtCuAO family members resulting in a range of developmental phenotypes including changes in leaf development, flowering time, stem morphology and silique production. We are currently analysing these lines, their stability and heritability.