DEVELOPMENTAL AND LIGHT-REGULATED EXPRESSION OF INDIVIDUAL MEMBERS OFTHE LIGHT-HARVESTING COMPLEX-B GENE FAMILY IN PINUS-PALUSTRIS

Angiosperms require light for multiple aspects of chloroplast developm ent, including chlorophyll synthesis and induction of expression of th e mRNAs encoding the major polypeptides of the light-harvesting comple x of photosystem II (Lhcb genes). In contrast, many conifers, includin g pines, firs, and spruces, can accumulate chlorophyll and the light-h arvesting chlorophyll a/b-binding proteins of photosystem II in comple te darkness. To understand the factors responsible for the regulation of expression of individual Lhcb mRNAs in the pine Pinus palustris, we have prepared sequence-specific cDNA probes for each of three family members, Lhcb1Pp1, Lhcb2*Pp1, and Lhcb2*Pp2, and have studied the exp ression of two of these, Lhcb1Pp1 and Lhcb2*Pp2, in detail. The level s of expression of each sequence were disparate, and Lhcb1Pp1-encoded transcripts were the most abundant in the light. Both Lhcb1Pp1 and L hcb2Pp2 mRNAs were expressed in stems and cotyledons, but Lhcb1*Pp1 m RNA was present at about 10-fold lower levels in stems than in cotyled ons, in contrast to Lhcb2Pp2 mRNA, which was expressed at higher leve ls in stems than in cotyledons. Both Lhcb1Pp1 and Lhcb2*Pp2 mRNAs wer e absent in embryos but were expressed during seedling development. Th e levels increased with age in both the light and the dark and in both cases were about 2-fold higher in the light than in the dark. Despite the expression of Lhcb1Pp1 and Lhcb2*Pp2 mRNAs during development in darkness, the levels of both mRNAs increased in dark-grown seedlings given red light in the low fluence range within 2 h of treatment.