MODIFYING CHRYSANTHEMUM (DENDRANTHEMA GRANDIFLORUM) GROWTH HABIT BY GENETIC MANIPULATION

The process by which plants respond to light signals is known as photomorphogenisis.
Phytochromes are one family of photoreceptor which detect changes in the red and far-red components of the light environment (phytochromes A-E) (Sharrock and Quail, 1989). Phytochromes have overlapping functions controlling processes including germination, etiolation and de-etiolation, shade avoidance and daylength perception.
The exact roles of phy C, D and E are unclear but mutant studies in Arabidopsis have shown that phytochrome A is involve in responses to far red (FR) light and that phytochrome B is involved in the response to red (R) light.

Phytochrome A is light labile and is most abundant in dark grown, etiolated tissue, over-expression can lead to an enhanced sensitivity to FR light and a consequent over-expression dwarf phenotype (Cherry et al., 1991).

Phytochrome B is a light stable phytochrome and the most abundant in light grown tissue, over-expression is an exaggerated response to R light, so that in normal light conditions phy B overexpression causes a light conditional, dark green, dwarfed phenotype (Wagner et al., 1991).

1.2 Phytochrome Genetic Manipulation

Overexpression of phytochrome genes in transgenic plants has several physiological effects including; decrease in stem elongation, increase in chlorophyll content, increased branching and delayed senescence (Boylan and Quail, 1991).

Interestingly both phytochrome A over-expression and phytochrome B mutants have been shown to have altered gibberellin levels and/or sensitivity.

In this study we decided to attempt to induce a dwarf phenotype in chrysanthemum by constitutively overexpressing rice phy A and arabidopsis phy B.