Department of Plant and Microbial Biology, University of California, Berkeley, California, USA.
Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA.
mBio. 2021 Mar 16;12(2):e00307-21. doi: 10.1128/mBio.00307-21.
Filamentous fungi undergo somatic cell fusion to create a syncytial, interconnected hyphal network which confers a fitness benefit during colony establishment. However, barriers to somatic cell fusion between genetically different cells have evolved that reduce invasion by parasites or exploitation by maladapted genetic entities (cheaters). Here, we identified a predicted mannosyltransferase, glycosyltransferase family 69 protein (GT69-2) that was required for somatic cell fusion in Cells lacking GT69-2 prematurely ceased chemotropic signaling and failed to complete cell wall dissolution and membrane merger in pairings with wild-type cells or between Δ cells (self fusion). However, loss-of-function mutations in the linked () locus suppressed the self-cell-fusion defects of Δ cells, although Δ Δ double mutants still failed to undergo fusion with wild-type cells. Both GT69-2 and RFW-1 localized to the Golgi apparatus. Genetic analyses indicated that RFW-1 negatively regulates cell wall remodeling-dependent processes, including cell wall dissolution during cell fusion, separation of conidia during asexual sporulation, and conidial germination. GT69-2 acts as an antagonizer to relieve or prevent negative functions on cell fusion by RFW-1. In species and populations, alleles of were highly polymorphic and fell into two discrete haplogroups. In all isolates within haplogroup I, was conserved and linked to All isolates within haplogroup II lacked These data indicated that are under balancing selection and provide new mechanisms regulating cell wall remodeling during cell fusion and conidial separation. Cell wall remodeling is a dynamic process that balances cell wall integrity versus cell wall dissolution. In filamentous fungi, cell wall dissolution is required for somatic cell fusion and conidial separation during asexual sporulation. In the filamentous fungus , allorecognition checkpoints regulate the cell fusion process between genetically different cells. Our study revealed two linked loci with transspecies polymorphisms and under coevolution, and , which form a coordinated system to regulate cell wall remodeling during somatic cell fusion, conidial separation, and asexual spore germination. RFW-1 acts as a negative regulator of these three processes, while GT69-2 functions antagonistically to RFW-1. Our findings provide new insight into the mechanisms involved in regulation of fungal cell wall remodeling during growth and development.
丝状真菌通过体细胞融合形成合胞体、相互连接的菌丝网络，这在菌落建立过程中赋予了适应性优势。然而，不同遗传背景的细胞之间融合的障碍已经进化，从而减少寄生虫的入侵或适应不良遗传实体（骗子）的利用。在这里，我们鉴定了一个预测的甘露糖基转移酶，糖基转移酶家族 69 蛋白（GT69-2），它是体细胞融合所必需的。缺乏 GT69-2 的细胞过早停止趋化信号，并且在与野生型细胞配对或在Δ细胞（自融合）之间不能完成细胞壁溶解和膜融合。然而，连接的（）位点的功能丧失突变抑制了Δ细胞的自细胞融合缺陷，尽管ΔΔ双突变体仍然不能与野生型细胞融合。GT69-2 和 RFW-1 都定位于高尔基体。遗传分析表明，RFW-1 负调控细胞壁重塑相关过程，包括细胞融合过程中的细胞壁溶解、无性孢子形成过程中分生孢子的分离以及分生孢子的萌发。GT69-2 作为拮抗剂发挥作用，通过 RFW-1 缓解或防止细胞融合的负功能。在物种和种群中，等位基因高度多态，分为两个离散的单倍型组。在单倍型组 I 中的所有分离株中，都保守并与相连所有属于单倍型组 II 的分离株都缺失了这些数据表明，是在平衡选择下，为细胞融合和分生孢子分离过程中细胞壁重塑提供了新的调控机制。细胞壁重塑是一个动态过程，平衡细胞壁完整性与细胞壁溶解。在丝状真菌中，细胞壁溶解是体细胞融合和无性孢子形成过程中分生孢子分离所必需的。在丝状真菌中，同种异体识别检查点调节不同遗传背景的细胞之间的细胞融合过程。我们的研究揭示了两个具有跨物种多态性和共同进化的连锁基因座，和，它们形成了一个协调的系统，调节体细胞融合、分生孢子分离和无性孢子萌发过程中的细胞壁重塑。RFW-1 作为这三个过程的负调节剂，而 GT69-2 则与 RFW-1 拮抗作用。我们的研究结果为真菌细胞壁重塑在生长和发育过程中的调控机制提供了新的见解。
