Stephen.pearce@rothamsted.ac.uk

The phytohormone gibberellin (GA) is an important regulator of plant growth and development. Bioactive GA levels are tightly regulated, in part by the activity of GA20oxidase and GA3oxidase enzymes that catalyze the final stages of GA biosynthesis. In wheat, both enzymes are encoded by multi-gene families that exhibit distinct expression profiles, allowing for precise spatial and temporal control of GA levels in different tissues.

We characterized the function of GA20ox and GA3ox genes in wheat using a collection of chemically-induced loss-of-function mutants. In replicated field experiments, we found that while GA20ox1 plays a minor role in wheat stem elongation, ga20ox2 mutants exhibit a reduction in height comparable to the Rht-D1b allele that may be useful as alternative semi-dwarfing alleles.

We found that GA3ox3 and GA1ox1 are highly expressed in grain tissues and act in concert to regulate bioactive GA levels during grain development.

In different mutant lines, bioactive GA levels were positively correlated with grain size and height. We characterized the natural genetic diversity in these genes among wheat landraces and identified haplotypes carrying major promoter rearrangements that confer an altered expression profile.

Our work sheds light on the function of different GA biosynthesis genes during wheat development and highlights the potential to select both natural and induced genetic variation in this pathway for crop improvement in breeding programs.