A FUSCA gene of Arabidopsis encodes a novel protein essential for plant development.

Arabidopsis fusca mutants display striking purple coloration due to anthocyanin accumulation in their cotyledons. We describe six recessive fusca mutants isolated from Agrobacterium-transformed Arabidopsis families. These mutants first become defective during embryogenesis and exhibit limited seedling development. Double mutant constructs revealed that developmental defects were not simply a consequence of anthocyanin accumulation. fusca seedlings showed altered responses to several environmental and endogenous factors. Allelism tests established that three fusca loci are represented by mutants previously described as defective in light-regulated responses. To study the molecular basis of the fusca phenotype, we cloned the FUS6 gene. FUS6 encodes a novel protein that is hydrophilic, alpha-helical, and contains potential protein kinase C phosphorylation sites. The FUSCA proteins appear to act in a network of signal transduction pathways critical for plant development.