PDF(Pubmed)
Abstract：
Dinoflagellates are responsible for most marine harmful algal blooms (HABs) and play vital roles in many ocean processes. More than 90% of dinoflagellates are vitamin B12 auxotrophs and that B12 availability can control dinoflagellate HABs, yet the genetic basis of B12 auxotrophy in dinoflagellates in the framework of the ecology of dinoflagellates and particularly HABs, which was the objective of this work. Here, we investigated the presence, phylogeny, and transcription of two methionine synthase genes (B12-dependent metH and B12-independent metE) via searching and assembling transcripts and genes from transcriptomic and genomic databases, cloning 38 cDNA isoforms of the two genes from 14 strains of dinoflagellates, measuring the expression at different scenarios of B12, and comprehensive phylogenetic analyses of more than 100 organisms. We found that 1) metH was present in all 58 dinoflagellates accessible and metE was present in 40 of 58 species, 2) all metE genes lacked N-terminal domains, 3) metE of dinoflagellates were phylogenetically distinct from other known metE genes, and 4) expression of metH in dinoflagellates was responsive to exogenous B12 levels while expression of metE was not responding as that of genuine metE genes. We conclude that most, hypothetically all, dinoflagellates have either non-functional metE genes lacking N-terminal domain for most species, or do not possess metE for other species, which provides the genetic basis for the widespread nature of B12 auxotrophy in dinoflagellates. The work elucidated a fundamental aspect of the nutritional ecology of dinoflagellates.
摘要：
鞭毛藻是大多数海洋有害藻华（HAB）的原因，并在许多海洋过程中起着至关重要的作用。超过90％的鞭毛藻是维生素B12营养缺陷型，并且B12的可用性可以控制鞭毛藻HABs，然而，在鞭毛藻，特别是HAB的生态学框架内，鞭毛藻中B12营养缺陷的遗传基础，这是这项工作的目的。这里,我们调查了存在，系统发育,通过从转录组和基因组数据库中搜索和组装转录本和基因，对两个甲硫氨酸合酶基因（依赖B12的metH和不依赖B12的metE）进行转录，从14个鞭毛藻菌株中克隆了两个基因的38个cDNA亚型，测量B12在不同情况下的表达，并对100多种生物进行全面的系统发育分析。我们发现1）metH存在于所有58种可接近的鞭毛藻中，而metE存在于58种物种中的40种，2)所有metE基因缺乏N端结构域，3）鞭毛藻的metE在系统发育上与其他已知的metE基因不同，和4）鞭毛藻中metH的表达对外源B12水平有反应，而metE的表达对真正的metE基因没有反应。我们得出结论，大多数，假设所有，对于大多数物种来说，鞭毛藻具有缺乏N末端结构域的无功能metE基因，或者不拥有其他物种的metE，这为鞭毛藻中B12营养缺陷型的广泛性质提供了遗传基础。这项工作阐明了鞭毛藻营养生态学的基本方面。
