No abstract

We examined chlL ~rxC) gene evolution using several approaches. Sequences from the chloroplast genome of the fern Polystichum acrostichoides and from the cyanobacterium Synechococcus sp. 7002 were determined and found to be highly conserved. A complete physical map of the fern chloroplast genome and partial maps of other vascular plant taxa show that chlL is located primarily in the small single copy region as in Marchantia polymorpha. A survey of a wide variety of non-angiospermous vascular plant DNAs shows that chlL is widely distributed but has been lost in the pteridophyte Psiloturn and (presumably independently) within the Gnetalean gymnosperms. Most green, chlorophyll-containing organisms have both a light-dependent and a light-independent pathway to chlorophyll (Chl) synthesis, due to the presence of two distinct enzymes for protochlorophyllide (PChlide) reduction. The broad spectrum of photosynthetic organisms capable of dark PChlide reduction includes the * The namefrxC was originally used to denote a gene encoding a product with probable Fe : S cluster binding activity. This activity was postulated due to the amino acid sequence similarity between this product and the Fe : S-binding nitrogenase iron protein nifH. Fe : Sbinding is a property shared by ferredoxins, which are denoted by the prefix "frx". However, this gene does not encode a ferredoxin. It is much larger than any known ferredoxin, it binds its Fe: S cluster between two halves of a homodimer (FuJITA & al. 1989, BURKE & al. 1993 a, c) instead of within a single subunit, and it lacks the pattern of clustered cysteines present in all ferredoxins (MEYER 1988). Therefore, we use the name chIL to recognize the sequence and functional similarities to the bacterial PChlide reductase subunit, bchL. Similar usage has been adopted for this (SuzuKI & BAUER 1992) and other (CHOQUET & al. 1992, BURKE & al. 1993 b) PChlide reductase subunits.