TRANSIENT EXPRESSION OF PHOTOSYNTHETIC GENES IN TRANSFECTED ALBINOID PETUNIA PROTOPLASTS AND CORRECT PROCESSING OF NEWLY SYNTHESIZED CHLOROPLAST-DESTINED POLYPEPTIDES

Protoplasts prepared from cultured albinoid cells of petunia do not ex press photosynthetic genes, such as those coding for chlorophyll a/b-b inding (Cab) proteins or ribulose-1,5-bisphosphate carboxylase/oxygena se (Rubisco). They therefore provide a convenient system for expressin g recombinant photosynthetic genes, without background interference. T ransfection of petunia protoplasts with vectors bearing the Lhcb11 Ca b gene under the control of the 35S promoter of cauliflower mosaic vir us (CaMV) resulted in the appearance of significant amounts of the spe cific transcripts, but not of the corresponding polypeptides, as infer red from northern and western blot analysis, respectively. The use of an expression vector carrying the translational enhancer OMEGA of toba cco mosaic virus (TMV) strongly enhanced the appearance of transfected gene products: western blot analysis of transfected protoplasts clear ly revealed the appearance of Lemna gibba Lhcb11 and Lhcb2*1, tomato Lhcb21 and psaD, and pea rbcS gene products. Molecular weight estimat ions of the newly synthesized polypeptides indicated that each was pro mptly processed into its mature-cleaved form within the transfected al binoid protoplasts. This occurred despite a lack of chlorophyll and th e absence of a thylakoid network.