Tobacco VDL gene encodes a plastid DEAD box RNA helicase and is involved in chloroplast differentiation and plant morphogenesis

The recessive nuclear vdl (for variegated and distorted leaf) mutant of tob acco was obtained by T-DNA insertion and characterized by variegated leaves and abnormal roots and flowers. Affected leaf tissues were white and disto rted, lacked palisadic cells, and contained undifferentiated plastids. The variegation was due to phenotypic, rather than genetic, instability. Genomi c and cDNA clones were obtained for both the mutant and wild-type VDL allel es. Three transcripts, resulting from alternate intron splicing or polyaden ylation, were found for the wild type. The transcripts potentially encode a set of proteins (53, 19, and 15 kD) sharing the same N-terminal region tha t contains a chloroplast transit peptide capable of importing the green flu orescent protein into chloroplasts. The predicted 53-kD product belongs to the DEAD box RNA helicase family. In the homozygous vdl mutant, T-DNA inser tion resulted in accumulation of the shortest transcript and the absence of the RNA helicase-encoding transcript. Genetic transformation of the homozy gous mutant by the 53-kD product-encoding cDNA fully restored the wild-type phenotype. These data suggest that a plastid RNA helicase controls early p lastid differentiation and plant morphogenesis.