MOLECULAR-CLONING OF A CAROTENOID-ASSOCIATED PROTEIN FROM CUCUMIS-SATIVUS COROLLAS - HOMOLOGOUS GENES INVOLVED IN CAROTENOID SEQUESTRATION IN CHROMOPLASTS

Chromoplasts are carotenoid-accumulating plastids found in the corolla s and fruits of many higher plants. In most cases, the pigment in thes e plastids is accumulated with the aid of carotenoid-associated protei ns located within unique structures. This paper reports the isolation and characterization of the cDNA (CHRC) from Cucumis sativus corollas which encodes the chromoplast-specific carotenoid-associated protein C HRC. The transit peptide cleavage site was determined and, using a chl oroplast uptake system, it is shown that CHRC can be post-translationa lly targeted to these plastids where it is peripherally associated wit h thylakoids. Analysis of CHRC transcript level in Cucumis sativus rev ealed its temporal and tissue-specific regulation: the transcript was detected only in corollas, where its level increased in parallel to fl ower development, peaking just before anthesis. CHRC shares significan t homology (59%) with the gene coding for fibrillin - a protein in Cap sicum annuum red fruits whose function is essentially identical to tha t of CHRC. A CHRC fragment including the potential active site of the protein was used as a probe in Northern blot analyses of floral and fr uit tissues from various plants containing chromoplasts of different t ypes: CHRC homologs of similar sizes were revealed in all cases. The e xistence of a group of homologous genes coding for chromoplast-specifi c proteins which aid in the sequestration of carotenoids within specif ic structures is proposed.