Almeida João M G C F, Cissé Ousmane H, Fonseca Álvaro, Pagni Marco, Hauser Philippe M
Centro de Recursos Microbiológicos (CREM), Departamento de Ciências da Vida, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal.
Institute of Microbiology, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland Vital-IT Group, SIB Swiss Institute of Bioinformatics, Lausanne, Switzerland.
mBio. 2015 Jan 13;6(1):e02250-14. doi: 10.1128/mBio.02250-14.
Pneumocystis species are fungal parasites of mammal lungs showing host specificity. Pneumocystis jirovecii colonizes humans and causes severe pneumonia in immunosuppressed individuals. In the absence of in vitro cultures, the life cycle of these fungi remains poorly known. Sexual reproduction probably occurs, but the system of this process and the mating type (MAT) genes involved are not characterized. In the present study, we used comparative genomics to investigate the issue in P. jirovecii and Pneumocystis carinii, the species infecting rats, as well as in their relative Taphrina deformans. We searched sex-related genes using 103 sequences from the relative Schizosaccharomyces pombe as queries. Genes homologous to several sex-related role categories were identified in all species investigated, further supporting sexuality in these organisms. Extensive in silico searches identified only three putative MAT genes in each species investigated (matMc, matMi, and matPi). In P. jirovecii, these genes clustered on the same contig, proving their contiguity in the genome. This organization seems compatible neither with heterothallism, because two different MAT loci on separate DNA molecules would have been detected, nor with secondary homothallism, because the latter involves generally more MAT genes. Consistently, we did not detect cis-acting sequences for mating type switching in secondary homothallism, and PCR revealed identical MAT genes in P. jirovecii isolates from six patients. A strong synteny of the genomic region surrounding the putative MAT genes exists between the two Pneumocystis species. Our results suggest the hypothesis that primary homothallism is the system of reproduction of Pneumocystis species and T. deformans.
Sexual reproduction among fungi can involve a single partner (homothallism) or two compatible partners (heterothallism). We investigated the issue in three pathogenic fungal relatives: Pneumocystis jirovecii, which causes severe pneumonia in immunocompromised humans; Pneumocystis carinii, which infects rats; and the plant pathogen Taphrina deformans. The nature, the number, and the organization within the genome of the genes involved in sexual reproduction were determined. The three species appeared to harbor a single genomic region gathering only three genes involved in sexual differentiation, an organization which is compatible with sexual reproduction involving a single partner. These findings illuminate the strategy adopted by fungal pathogens to infect their hosts.
肺孢子菌属是哺乳动物肺部的真菌寄生虫，具有宿主特异性。耶氏肺孢子菌寄生于人类，可在免疫抑制个体中引起严重肺炎。由于缺乏体外培养方法，这些真菌的生命周期仍鲜为人知。可能存在有性繁殖，但该过程的系统以及涉及的交配型（MAT）基因尚未得到表征。在本研究中，我们利用比较基因组学来研究耶氏肺孢子菌、感染大鼠的卡氏肺孢子菌以及它们的亲缘种畸形外囊菌中的这一问题。我们以来自相关粟酒裂殖酵母的103个序列作为查询序列来搜索与性别相关的基因。在所有研究的物种中都鉴定出了与几个性别相关角色类别同源的基因，进一步支持了这些生物体中存在有性生殖。广泛的电子搜索在每个研究物种中仅鉴定出三个假定的MAT基因（matMc、matMi和matPi）。在耶氏肺孢子菌中，这些基因聚集在同一条重叠群上，证明了它们在基因组中的相邻性。这种组织方式似乎既不符合异宗配合，因为如果是异宗配合，在不同的DNA分子上会检测到两个不同的MAT位点；也不符合次生同宗配合，因为次生同宗配合通常涉及更多的MAT基因。一致的是，我们没有检测到次生同宗配合中交配型转换的顺式作用序列，并且PCR显示来自六名患者的耶氏肺孢子菌分离株中的MAT基因相同。两种肺孢子菌物种中假定的MAT基因周围的基因组区域存在很强的共线性。我们的结果提出了一个假说，即原生同宗配合是肺孢子菌属和畸形外囊菌的繁殖系统。
真菌中的有性繁殖可以涉及单个亲本（同宗配合）或两个兼容亲本（异宗配合）。我们在三种致病性真菌亲缘种中研究了这一问题：可在免疫受损人类中引起严重肺炎的耶氏肺孢子菌；感染大鼠的卡氏肺孢子菌；以及植物病原体畸形外囊菌。确定了参与有性繁殖的基因在基因组中的性质、数量和组织方式。这三个物种似乎都有一个单一的基因组区域，仅包含三个参与性别分化的基因，这种组织方式与涉及单个亲本的有性繁殖相兼容。这些发现阐明了真菌病原体感染宿主所采用的策略。
