Department of Biology, Indiana University, Bloomington, Indiana 47405-3700, USA.
Mycologia. 2010 Nov-Dec;102(6):1497-509. doi: 10.3852/10-011. Epub 2010 May 26.
In a phylogenetic study of arbuscular mycorrhizal fungal species in Acaulospora (Acaulosporaceae, Glomeromycota) we discovered that species classified in genus Kuklospora, a supposed sister clade of Acaulospora, did not partition as a monophyletic clade. Species in these two genera can be distinguished only by the position of the spore relative to a precursor structure, the sporiferous saccule, as either within (entrophosporoid) or laterally (acaulosporoid) on the saccule subtending hypha. Subsequent spore differentiation follows identical patterns and organization. Molecular phylogeny reconstructed from nrLSU gene sequences, together with developmental data, support the hypothesis that the entrophosporoid mode of spore formation evolved many times and thus represents a convergent trait of little phylogenetic significance. Therefore genus Kuklospora is rejected as a valid monophyletic group and it is integrated taxonomically into genus Acaulospora. Thus Acaulospora colombiana and Acaulospora kentinensis are erected as new combinations (formerly Kuklospora colombiana and Kuklospora kentinensis). Mode of spore formation is demoted from a genus-specific character to one that is included with other traits to define Acaulospora species. In addition we describe a new AM fungal species, Acaulospora colliculosa (Acaulosporaceae), that originated from a tallgrass prairie in North America. Field-collected spores of A. colliculosa are small (<100 μm diam), hyaline or subhyaline to pale yellow and form via entrophosporoid development based on structure and organization of cicatrices and attached hyphae. Each spore consists of a bilayered spore wall and two bilayered inner walls. A germination orb likely forms after the completion of spore development to initiate germination, but this structure was not observed. A character distinguishing A. colliculosa from other Acaulospora species is hyaline to subhyaline hemispherical protuberances on the surface of the outer spore wall layer. A phylogeny reconstructed from partial nrLSU gene sequences unambiguously placed A. colliculosa in the Acaulospora clade.
在一项关于丛枝菌根真菌（球囊霉科，球囊霉门）的系统发育研究中，我们发现，被归类于 Kuklospora 属的物种并没有形成一个单系群，而 Kuklospora 属被认为是丛枝菌根真菌的姐妹群。这两个属的物种只能通过孢子相对于前驱结构（孢子囊）的位置来区分，孢子位于孢子囊下方的菌丝的内部（内生孢子型）或侧面（外生孢子型）。随后的孢子分化遵循相同的模式和组织。基于 nrLSU 基因序列重建的分子系统发育，以及发育数据，支持了内生孢子形成模式多次进化的假说，因此内生孢子形成模式代表了一个具有较小系统发育意义的趋同特征。因此，Kuklospora 属被拒绝作为一个有效的单系群，它在分类学上被整合到丛枝菌根真菌属中。因此，Acaulospora colombiana 和 Acaulospora kentinensis 被确立为新的组合（以前是 Kuklospora colombiana 和 Kuklospora kentinensis）。孢子形成模式从一个属特异性特征降级为一个与其他特征一起定义丛枝菌根真菌属物种的特征。此外，我们描述了一种来自北美的新的丛枝菌根真菌物种，Acaulospora colliculosa（球囊霉科）。采集的 A. colliculosa 孢子很小（<100 μm 直径），透明或半透明至淡黄色，通过内生孢子形成发育，基于疤痕和附着菌丝的结构和组织。每个孢子由双层孢子壁和两层双层内壁组成。一个萌发球体可能在孢子发育完成后形成，以启动萌发，但这个结构没有被观察到。A. colliculosa 与其他丛枝菌根真菌物种的一个区别特征是在外层孢子壁层的表面有透明至半透明的半球形突起。基于部分 nrLSU 基因序列重建的系统发育树明确将 A. colliculosa 置于丛枝菌根真菌属中。
