Department of Forest Sciences, University of Helsinki, Helsinki, Finland.
BMC Evol Biol. 2013 Nov 4;13:240. doi: 10.1186/1471-2148-13-240.
Hydrophobins are small secreted cysteine-rich proteins that play diverse roles during different phases of fungal life cycle. In basidiomycetes, hydrophobin-encoding genes often form large multigene families with up to 40 members. The evolutionary forces driving hydrophobin gene expansion and diversification in basidiomycetes are poorly understood. The functional roles of individual genes within such gene families also remain unclear. The relationship between the hydrophobin gene number, the genome size and the lifestyle of respective fungal species has not yet been thoroughly investigated. Here, we present results of our survey of hydrophobin gene families in two species of wood-degrading basidiomycetes, Phlebia brevispora and Heterobasidion annosum s.l. We have also investigated the regulatory pattern of hydrophobin-encoding genes from H. annosum s.s. during saprotrophic growth on pine wood as well as on culture filtrate from Phlebiopsis gigantea using micro-arrays. These data are supplemented by results of the protein structure modeling for a representative set of hydrophobins.
We have identified hydrophobin genes from the genomes of two wood-degrading species of basidiomycetes, Heterobasidion irregulare, representing one of the microspecies within the aggregate H. annosum s.l., and Phlebia brevispora. Although a high number of hydrophobin-encoding genes were observed in H. irregulare (16 copies), a remarkable expansion of these genes was recorded in P. brevispora (26 copies). A significant expansion of hydrophobin-encoding genes in other analyzed basidiomycetes was also documented (1-40 copies), whereas contraction through gene loss was observed among the analyzed ascomycetes (1-11 copies). Our phylogenetic analysis confirmed the important role of gene duplication events in the evolution of hydrophobins in basidiomycetes. Increased number of hydrophobin-encoding genes appears to have been linked to the species' ecological strategy, with the non-pathogenic fungi having increased numbers of hydrophobins compared with their pathogenic counterparts. However, there was no significant relationship between the number of hydrophobin-encoding genes and genome size. Furthermore, our results revealed significant differences in the expression levels of the 16 H. annosum s.s. hydrophobin-encoding genes which suggest possible differences in their regulatory patterns.
A considerable expansion of the hydrophobin-encoding genes in basidiomycetes has been observed. The distribution and number of hydrophobin-encoding genes in the analyzed species may be connected to their ecological preferences. Results of our analysis also have shown that H. annosum s.l. hydrophobin-encoding genes may be under positive selection. Our gene expression analysis revealed differential expression of H. annosum s.s. hydrophobin genes under different growth conditions, indicating their possible functional diversification.
疏水性蛋白是一种小的分泌型富含半胱氨酸的蛋白质，在真菌生命周期的不同阶段发挥着多种作用。在担子菌中，疏水性蛋白编码基因通常形成多达 40 个成员的大型多基因家族。驱动担子菌疏水性蛋白基因扩张和多样化的进化力量还不太清楚。此类基因家族中单个基因的功能作用也不清楚。尚未彻底研究疏水性蛋白基因数量与真菌物种的基因组大小和生活方式之间的关系。在这里，我们展示了对两种木质降解担子菌，Phlebia brevispora 和 Heterobasidion annosum s.l.的疏水性蛋白家族的研究结果。我们还研究了 H. annosum s.s.在松木上腐生生长以及在 Phlebiopsis gigantea 培养液中时，疏水性蛋白编码基因的调控模式，使用了微阵列。这些数据补充了代表性疏水性蛋白集的蛋白质结构建模结果。
我们从木质降解担子菌 Heterobasidion irregulare 和 Phlebia brevispora 的基因组中鉴定出了疏水性蛋白基因。Heterobasidion irregulare 中观察到大量的疏水性蛋白编码基因（16 个拷贝），而 Phlebia brevispora 中这些基因的显著扩张（26 个拷贝）。在其他分析的担子菌中也记录了疏水性蛋白编码基因的大量扩张（1-40 个拷贝），而在分析的子囊菌中则观察到通过基因丢失导致的收缩（1-11 个拷贝）。我们的系统发育分析证实了基因复制事件在担子菌中疏水性蛋白进化中的重要作用。疏水性蛋白编码基因数量的增加似乎与物种的生态策略有关，与致病性真菌相比，非致病性真菌的疏水性蛋白数量增加。然而，疏水性蛋白编码基因的数量与基因组大小之间没有显著关系。此外，我们的结果表明，H. annosum s.s.的 16 个疏水性蛋白编码基因的表达水平存在显著差异，这表明它们的调控模式可能存在差异。
在担子菌中观察到疏水性蛋白编码基因的大量扩张。分析物种中疏水性蛋白编码基因的分布和数量可能与它们的生态偏好有关。我们的分析结果还表明，H. annosum s.l.的疏水性蛋白编码基因可能受到正选择。我们的基因表达分析表明，在不同的生长条件下，H. annosum s.s.的疏水性蛋白基因表达存在差异，表明它们可能具有功能多样化。
