Light-Regulated and Organ-Specific Expression of Types 1, 2, and 3 Light-Harvesting Complex b mRNAs in Ginkgo biloba

Abstract

In a prior study (E. Chinn and J. Silverthorne [1993] Plant Physiol 103: 727-732) we showed that the gymnosperm Ginkgo biloba was completely dependent on light for chlorophyll synthesis and chloroplast development and that expression of light-harvesting complex b (Lhcb) mRNAs was substantially increased by light. However, dark-grown seedlings that were transferred to constant white light took significantly longer than angiosperm seedlings to initiate a program of photomorphogenesis and the stems failed to green completely. We have prepared type-specific probes for mRNAs encoding major polypeptides of light-harvesting complex II (Lhcbl, Lhcb2, and Lhcb3) and have used these to analyze the expression of individual Lhcb mRNAs during greening. All three sequences accumulated in the top portions of dark-grown seedlings transferred to light, but, as was seen previously for total Lhcb mRNAs, there was a transient, reproducible decline in the levels of all three mRNAs after 4 d in the light. This transient decrease in Lhcb mRNA levels was not paralleled by a decrease in Chl accumulation. By contrast, there were significantly lower levels of all three Lhcb mRNAs i n the lower portions of greening dark-grown stems as well as lower Chl levels. We conclude that although the tops of the plants have the capacity to etiolate and green, Gingko seedling stems continue a program of development into woody tissue in darkness that precludes greening when the seedlings are transferred to the light.Light plays a central role in the induction of chloroplast development and expression of nuclear-encoded chloroplast polypeptides in flowering plants (reviewed by Sundqvist and Ryberg, 1993). In particular, light is required for the synthesis and assembly of the two photosystems, termed PSI and PSII, and their associated light-harvesting complexes, LHCI and LHCII. The major components of these thylakoid membrane complexes are the light-harvesting Chl alb-binding proteins that serve to bind Chls a and b as well as other accessory pigments such as carotenoids (Thornber et al., 1994). The best-characterized members of this superfamily of related polypeptides are the LHCIIb

Origins of Phytochrome-Modulated Lhcb mRNA Expression in Seed Plants

“…Similar absolute expression levels have been reported for tomato (Lycopersicon esculentum), in which total steady-state Lhcb mRNA levels in light leaf was approximately 0.75 fmol g Ϫ1 total RNA (Kellmann et al, 1993). These values are in accordance with those determined in a previous study for the absolute value of Lhcb mRNA in light-grown G. biloba leaf (approximately 0.14 fmol g Ϫ1 total RNA; Chinn et al, 1995). However, through analysis of Lhcb expression in this and a parallel study (S. Christensen, E. LaVerne, G. Boyd, and J. Silverthorne, unpublished data), it is apparent that large variations in response timing and magnitude exist (a) between independent light treatments on the same batch of seedlings, and (b) between seedlings from different batches of seed.…”

“…The relative abundance of Lhcb1, Lhcb2, and Lhcb3 mRNAs in light-grown leaf was determined in a previous study (Chinn et al, 1995). Lhcb1 mRNA was found to be the most abundant species, representing approximately 0.14 femto mol g Ϫ1 total mRNA, whereas Lhcb2 and Lhcb3 mRNAs were found to be expressed at 10-to 15-fold lower levels (approximately 10 atto mol g Ϫ1 total mRNA).…”

“…However, it accumulates very low protochlorophyllide amounts in D (Mariani and Rascio, 1982) and takes up to 2 weeks to green completely upon exposure to continuous white light (W). Type-specific probes have been prepared for Lhcb1, Lhcb2, and Lhcb3 genes and using these, it has been shown that the levels of all three mRNAs increase during greening (Chinn et al, 1995). Using the induction of Lhcb gene expression as an assay for phytochrome function, we set out to determine whether this nonflowering, seed-bearing plant has the responses characteristic of phytochrome action in flowering plants.…”

Developmental and Light-Regulated Expression of Individual Members of the Light-Harvesting Complex b Gene Family in Pinus palustris

“…When a similar comparison was made using the type 2 pine sequences, Lhcb2*Ppl was 86 to 99% identical with other pine sequences and Lhcb2*Pp2 was 95 to 98% identical. The P. palustris Lhcb sequences were also closely related to G. biloba type 1 and type 2 Lhcb sequences, showing between 85 and 97% identity at the amino acid level (Chinn and Silverthorne, 1993;Chinn et al, 1995). Since a previous study of LHCIIb accumulation in P. palustris indicated that the major polypeptides were expressed in the absence of light (Canovas et al, 1993), sequence-specific probes were constructed to determine whether individual Lhcb mRNAs are also expressed in the absence of light.…”

An undergraduate laboratory exercise to study the effect of darkness on plant gene expression using DNA microarray

“…Micrograph of a small section of a 22K Arabidopsis DNA microarray hybridized with labeled cRNAs from the control (Cy3) and dark-treated (Cy5) plants. The microarray was scanned using an Agilent scanner to produce the image, which was then analyzed to identify up-regulated (red-spot) or down-regulated (green spots) gene expression in the darktreated Brassica rapa as shown in Table 1. tein complex in Photosystem II (PSII) [9]. The protein is located in the thylakoid membrane and is significant in allowing the thylakoid to collect the light and deliver the derived excitation energy to PSII in a controlled manner.…”