Jam packed genomes - a preliminary, comparative analysis of nucleomorphs

被引:56
作者
Gilson, PR
McFadden, GI [1 ]
机构
[1] Univ Melbourne, Sch Bot, Plant Cell Biol Res Ctr, Parkville, Vic 3010, Australia
[2] Deakin Univ, Sch Biol & Chem Sci, Ctr Cellular & Mol Biol, Geelong, Vic 3125, Australia
基金
澳大利亚研究理事会;
关键词
chloroplast; chlorarachniophyte; cryptomonad; C-value enigma; endosymbiosis; intron; mitosis; nucleomorph; photosynthesis; secondary plastid; telomere; transposable element;
D O I
10.1023/A:1016011812442
中图分类号
Q3 [遗传学];
学科分类号
071007 ; 090102 ;
摘要
There are two ways eukaryotic cells can permanently acquire chloroplasts. They can take up a cyanobacterium and turn it into a chloroplast or they can engulf an alga that already has a chloroplast. The second method is far more common and there are at least seven major groups of protists that have obtained their chloroplasts, this way. In most cases little remains of the engulfed alga apart from its chloroplast, but in two groups, the cryptomonads and chlorarachniophytes, a small remnant nucleus of the engulfed alga is still present. These tiny nuclei, called nucleomorphs, are the smallest and most compact eukaryotic genomes known and recently the nucleomorph of the cryptomonad alga Guillardia theta, was completely sequenced (551 kilobases). The nucleomorph of the chlorarachniophyte Bigellowiella natans (380 kilobases), is also being sequenced and is about half complete. We discuss some of the similarities and differences that are emerging between these two nucleomorph genomes. Both genomes contain just three chromosomes that encode mainly housekeeping genes and a few proteins for chloroplast functions. The bulk of nucleomorph gene coding capacity, therefore, appears to be devoted to self perpetuation and creating gene and protein expression machineries to make a small number of essential chloroplast proteins. We discuss reasons why both nucleomorphs are extraordinarily compact and why their gene sequences are evolving rapidly.
引用
收藏
页码:13 / 28
页数:16
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