• 作者： J.G.H. wessels
• 作者服務機構： Department of Plant Biology; University of Groningen
• 中文摘要： 向外分泌分解酵素是絲狀真菌維持生命延續的必要過程。在自然界中絲狀真菌是利用有機聚合物來增殖，但此類大分子成分必須在細胞外先被分解。細胞學上的證據顯示，此類酵素是經由在菌絲生長頂端與原生質膜相聯的泡囊向外分泌到細胞外。在過去的報告中，我們發現生長中的菌絲頂端確實存在大量將分泌到外的酵素。關於菌絲體恆態生長的理論，我們提出以下的假說，認為酵素是經由大量的含有組成細胞壁成分的原生質流動，由生長中的菌絲頂端向外分泌。 絲狀真菌向外分泌蛋白質的作用，對整個菌絲體而言，具有許多不同的活性表現，其中包括菌絲體的形態分化作用。在將產生氣生菌絲和子實體時期大量表現的基因選殖後，我們發現一類特殊的疏水性蛋白質－hydrophobins，此類蛋白質只在菌絲體生長已達成熟期時才產生。此時浸漬在培養基中的菌絲分泌出此種蛋白質的單體到培養基中，單體蛋白質間自動的聚集在一起形成一層水不溶性的複合體，結合在突出水面的菌絲細胞壁上。在氣生菌絲中一種特殊的hydrophobin包裹在菌絲體外形成不通透層。而在子實體形成時，另一種hydrophobin會生成，其作用可能與菌絲間的凝聚而形成多細胞的組織有關。除了參予前述形態分化的特殊作用外，此類hydrophobin除了可能也具有使菌絲和外界環境隔離的作用外，並會將同化的菌絲體轉變產生不同分化的構造，以進行水分和營養的傳送。
• 英文摘要： Excretion of lytic enzymes is a vital process in filamentous fungi because, in nature, they thrive onorganic polymers which must be degraded extracellularly. Cytological data suggest that such enzymes areexocytosed by the vesicles that continuously fuse with the plasma membrane at the growing apex. We haveshown that a large portion of the excreted enzymes indeed leaves the hypha at the growing apex. In relationto the steady-state growth theory, we hypothesize that enzymes can pass the wall at the growing apex bybulk flow, that is, by being carried by the flow of plastic wall material, making pores in the wall less im-portant than previously thought. Proteins excreted by filamentous fungi also serve a variety of other functions in the whole mycelium,including morphogenesis. By cloning genes abundantly expressed during formation of aerial hyphae andfruit bodies, we discovered a class of proteins, named hydrophobins, which are only produced when themycelium has reached a certain stage of maturity. Whilst excreted by submerged hyphae as monomersinto the medium, they self-assemble into insoluble complexes in the walls of emergent hyphae. In aerialhyphae, a particular hydrophobin takes the form of rodlets coating the hyphae, probably with an im-permeable layer. During fruit-body formation, other hydrophobins are produced which may function in theaggregation of hyphae to form the multicellular tissue. Apart from such specific morphogenetic functions,the hydrophobins may play a general role in insulating hyphae from the environment, converting the dif-ferentiating structures into sinks for translocation of water and nutrients from the assimilating mycelium.
• 中文關鍵字： fungal cell wall; tip growth; cell-wall assembly; protein excretion in fungi; hydrophobins; fruit-body formation; emergent growth in fungi.
• 英文關鍵字： --