MOLECULAR CHARACTERIZATION OF THE MITOCHONDRIAL CITRATE SYNTHASE GENEOF AN ACIDLESS POMELO (CITRUS-MAXIMA)

Pummelo (Citrus maxima [Burm.] Merrill) cDNAs encoding mitochondrial c itrate synthase (mCS) were cloned by reverse transcription of juice-sa c poly(A)(+) mRNA, followed by Taq Polymerase-mediated amplification. The nucleotide sequence of the citrus gene (citl) is 77% conserved rel ative to plant mRNAs for mCS. The encoded polypeptide includes a mitoc hondrial targeting signal at its amino terminus; all 20 putative activ e-site residues of the citrus enzyme are conserved. Southern hybridiza tion showed that citrus citl is a single-copy gene. A polymorphism ass ociated with citl did not cosegregate with fruit acidity indicating th at acitric, the gene causing the acidless phenotype of pummelo 2240, i s not an allele of citl locus. Quantitative detection of cirl mRNA sho wed that transcript levels are not developmentally regulated in juice sacs; no differences were observed between high- and low-acid genotype s.