Partial complementation of embryo defective mutations: a general strategy to elucidate gene function

The EMB 506 gene has been characterised as essential for embryo development . To provide insights into the role of EMB 506, which is hidden by the embr yo defective phenotype, the ABI3 promoter was fused to the EMB 506 cDNA. Th e expression of such a transgene should provide sufficient protein during e mbryogenesis to ensure normal embryo development in homozygous emb 506 seed s. We show that homozygous emb 506 seedlings, partially complemented with t he ABI3::EMB 506 transgene, can be obtained. Most of the rescued emb 506 pl ants are able to flower and to set normal seeds, but show mild to severe de pigmentation of rosette leaves and/or inflorescences. This effect on chloro plast development indicated a putative chloroplast localisation of the EMB 506 protein, which was demonstrated by GFP-protein fusion. However, EMB 506 cannot be considered as a chloroplast housekeeping protein only, since EMB 506 is not present in all photosynthetic tissues. This study demonstrates the power of this simple strategy, which could be widely applied to other e mb mutants and which may reveal similar or additional roles for EMB genes a t vegetative stages of the life cycle.