Lockhart P J, Larkum A W, Steel M, Waddell P J, Penny D
Molecular Genetics Unit, School of Biological Sciences, Massey University, Palmerston North New Zealand.
Proc Natl Acad Sci U S A. 1996 Mar 5;93(5):1930-4. doi: 10.1073/pnas.93.5.1930.
Competing hypotheses seek to explain the evolution of oxygenic and anoxygenic processes of photosynthesis. Since chlorophyll is less reduced and precedes bacteriochlorophyll on the modern biosynthetic pathway, it has been proposed that chlorophyll preceded bacteriochlorophyll in its evolution. However, recent analyses of nucleotide sequences that encode chlorophyll and bacteriochlorophyll biosynthetic enzymes appear to provide support for an alternative hypothesis. This is that the evolution of bacteriochlorophyll occurred earlier than the evolution of chlorophyll. Here we demonstrate that the presence of invariant sites in sequence datasets leads to inconsistency in tree building (including maximum-likelihood methods). Homologous sequences with different biological functions often share invariant sites at the same nucleotide positions. However, different constraints can also result in additional invariant sites unique to the genes, which have specific and different biological functions. Consequently, the distribution of these sites can be uneven between the different types of homologous genes. The presence of invariant sites, shared by related biosynthetic genes as well as those unique to only some of these genes, has misled the recent evolutionary analysis of oxygenic and anoxygenic photosynthetic pigments. We evaluate an alternative scheme for the evolution of chlorophyll and bacteriochlorophyll.
相互竞争的假说试图解释光合作用中含氧和无氧过程的进化。由于叶绿素在现代生物合成途径中还原程度较低且先于细菌叶绿素出现，因此有人提出叶绿素在进化过程中先于细菌叶绿素出现。然而，最近对编码叶绿素和细菌叶绿素生物合成酶的核苷酸序列的分析似乎为另一种假说提供了支持。即细菌叶绿素的进化早于叶绿素的进化。在这里，我们证明序列数据集中不变位点的存在会导致建树（包括最大似然法）出现不一致。具有不同生物学功能的同源序列通常在相同核苷酸位置共享不变位点。然而，不同的限制条件也可能导致基因特有的额外不变位点，这些基因具有特定且不同的生物学功能。因此，这些位点在不同类型的同源基因之间的分布可能不均匀。相关生物合成基因共享的不变位点以及仅某些此类基因特有的不变位点的存在，误导了最近对含氧和无氧光合色素的进化分析。我们评估了叶绿素和细菌叶绿素进化的另一种方案。
