Major alteration of the expression site of endogenous cellulases in members of an apical termite lineage
Major alteration of the expression site of endogenous cellulases in members of an apical termite lineage
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DOI：
10.1111/j.1365-294x.2004.02276.x
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发表时间：
2004-10-01
影响因子：
4.9
通讯作者：
Noda, H
中科院分区：
文献类型：
--
作者：
Tokuda, G;Lo, N;Noda, H
白蚁是地球上最重要的纤维素消化动物之一，并且以它们与纤维素分解性毛滴虫和氧化单胞菌鞭毛虫（单细胞真核生物）的共生关系而闻名。也许不太为人所知的事实是，在所描述的2600种类似的白蚁物种中，有75%属于白蚁科的物种并没有这种鞭毛虫。与其他科的大多数白蚁不同，大多数白蚁不消耗木材，而是以土壤，落叶，真菌，草或地衣为食。近年来已经看到的内源性纤维素酶，帮助白蚁消化纤维素的表征，从一个鞭毛窝藏物种（散白蚁speratus），以及一个白蚁（Nasutitermes takasagoensis）。这两种白蚁体内编码酶的基因是相似的。然而，它们的表达部位明显不同-在R. speratus和中肠;高砂子。为了进一步研究这种差异，我们进行了比较研究，纤维素酶的表达在各种白蚁和鞭毛窝藏物种，使用酶测定和逆转录聚合酶链反应。一致地发现，从taggenetically基底谱系的类群表达内源性基因，特别是在唾液腺，而那些从一个相对顶端的谱系白蚁表达纤维素酶只在中肠。相对较低水平的纤维素酶活性被发现在非木材喂养的物种，而木材喂养的Coptotermes formosanus-可以说是世界上最具破坏性的害虫物种-被发现有高水平的活动在肠道的所有部分相比，所有其他白蚁。根据这些结果，以及最近积累的系统发育数据，我们讨论了白蚁纤维素消化的演变方案。
Termites are among the most important cellulose-digesting animals on earth, and are well-known for the symbiotic relationship they have with cellulolytic trichomonad and oxymonad flagellates (unicellular eukaryotes). Perhaps less well-known is the fact that similar to75% of the similar to2600 described termite species - those belonging to the family Termitidae - do not harbour such flagellates. Unlike most termites from other families, the majority of termitids do not consume wood, feeding instead on soil, leaf litter, fungi, grass, or lichen. Recent years have seen the characterization of the endogenous cellulase enzymes that help termites digest cellulose, from one flagellate-harbouring species (Reticulitermes speratus), as well as one termitid (Nasutitermes takasagoensis). The genes encoding the enzymes in these two termites are similar. However, their site of expression differs markedly - the salivary glands in R. speratus and the midgut in N. takasagoensis. To investigate this difference further, we performed a comparative study of cellulase expression in various termitid and flagellate-harbouring species, using enzyme assays and reverse transcription polymerase chain reactions. Taxa from phylogenetically basal lineages were consistently found to express endogenous genes specifically in the salivary glands, whilst those from a relatively apical lineage containing termitids expressed cellulases solely in the midgut. Relatively low levels of cellulase activity were found in nonwood-feeding species, while the wood-feeding Coptotermes formosanus- arguably the most destructive pest species world-wide - was found to have high levels of activity in all parts of the gut when compared to all other termites. In the light of these results, as well as recently accumulated phylogenetic data, we discuss scenarios for the evolution of cellulose digestion in termites.