The peroxisomal glycolate oxidase gene is differentially expressed in yellow and white sectors of the D(P1) variegated tobacco mutant

The D(P1) variegated mutant of Nicotiana tabacum contains translationally defective plastids in its white (W) leaf sectors. In the present study a second type of pigment-deficient sector displaying a pale-yellow color (Y sectors) was discerned. Chlorophyll and carotenoids contents in both leaf sectors are very low, although the Y sectors contain twice the carotenoid content of the W sectors. Rubisco large subunit polypeptide content is low in the W sectors, while in the Y sectors its content is comparable to that in the green sectors. However, both leaf sector types do not show photosynthetic activity under ambient CO₂ concentration. The W and Y sectors exhibit 40 and 50% reduction in the level of the mRNA encoding the peroxisomal glycolate oxidase (GLO) enzyme, respectively. However, in the W sectors GLO activity and protein levels reached only 30% of that in the green sectors while in the Y sectors they almost reached the green sectors levels. It is suggested that the reduction in GLO mRNA levels in the Y and W sectors is resulted from inhibition of the putative plastid to nucleus signal. Post-transcriptional mechanism(s) that also regulate GLO gene expression may explain the discrepancies between GLO mRNA and GLO protein levels, as observed between the W, Y and green leaf sectors of the D(P1) mutant.