Unconventional secretion has emerged as an increasingly important cellular process in eukaryotic cells. The underlying translocation mechanisms are diverse and often little understood. We study unconventional secretion of chitinase Cts1 in the corn smut fungus Ustilago maydis. This protein participates in the cytokinesis of yeast cells. During budding it localizes to the septated fragmentation zone where it presumably functions in the degradation of remnant chitin to allow separation of mother and daughter cell. However, the mechanistic details of Cts1 export remain unclear.

Here we investigated the mechanism of unconventional Cts1 secretion with a focus on cytokinesis. Cell-cycle inhibition experiments supported the hypothesis that Cts1 export is connected to cytokinesis. To substantiate this finding we analysed gene deletion mutants impaired in cell separation and discovered that strains defective in secondary septum formation were affected in Cts1 export. The germinal centre kinase Don3 had a particularly strong influence on unconventional secretion. Using a synthetic switch, we unambiguously verified an essential role of Don3 for cytokinesis-dependent Cts1 export via the fragmentation zone. Thus, we gained novel insights into the mechanism of unconventional secretion and discovered the first regulatory component of this process.

非常规分泌已成为真核细胞中越来越重要的细胞过程。潜在的易位机制是多种多样的，并且通常很少被理解。我们研究了玉米黑穗病菌乌氏菌（Ustilago maydis）中几丁质酶Cts1的非常规分泌。该蛋白质参与酵母细胞的胞质分裂。在出芽期间，它定位于分隔的片段化区，在这里它可能在残余几丁质的降解中起作用，以允许母细胞和子细胞的分离。但是，尚不清楚Cts1出口的机械细节。

在这里，我们研究了非常规Cts1分泌的机制，重点是胞质分裂。细胞周期抑制实验支持Cts1输出与胞质分裂有关的假说。为了证实这一发现，我们分析了细胞分离受损的基因缺失突变体，并发现次生隔膜形成缺陷的菌株在Cts1输出中受到影响。生发中心激酶Don3对非常规分泌有特别强的影响。使用合成开关，我们明确验证了Don3在经由分裂区的胞质分裂依赖性Cts1出口中的重要作用。因此，我们获得了对非常规分泌机制的新颖见解，并发现了该过程的第一个调控成分。