Retrograde signalling in a virescent mutant triggers an anterograde delay of chloroplast biogenesis that requires GUN1 and is essential for survival.

Defects in chloroplast development are 'retrograde-signalled' to the nucleus, reducing synthesis of photosynthetic or related proteins. The mutant manifests virescence, a slow-greening phenotype, and is defective at an early stage in plastid development. Greening cotyledons or early leaf cells of exhibit immature chloroplasts which fail to fill the available cellular space.