植物病毒引发各种疾病症状，严重影响农业，但植物病毒引发病害的机制尚不明确。小牛病是菖蒲中的一种疾病，表现为伴有异位木质化细胞和导管组织（如木质部）的瘤的形成。在这里，我们展示了菖蒲小牛病相关病毒的基因片段，被指定为诱发小牛病因子(KOBU)，可以在烟草露兰兰中诱导伴有异位木质化细胞和类木质化组织的瘤的形成。表达KOBU的转基因菖蒲显示出肿瘤症状，证实了KOBU的瘤形成活性。令人惊讶的是，KOBU的表达还可以在正常的烟草露兰兰和菖蒲叶片的叶脉背面诱导形成额外的类叶组织。通过与表达KOBU的拟南芥的转录组分析，我们发现KOBU激活调控木质化细胞发育的信号通路。KOBU蛋白形成颗粒状和板状结构，并在细胞核内与mRNA剪接因子共定位。我们的发现表明，KOBU是一个新的多性病原因子，可以促进维管和叶片的发育。 在植物病毒-寄主组合中，各种机制决定了植物病毒引发的病症，而植物病毒如何引发症状的细节在大多数植物物种中仍然不清楚。小牛病是菖蒲中的一种疾病，表现为伴有异位木质化细胞和导管组织（如木质部）的瘤的形成。我们的发现证实了菖蒲小牛病相关病毒（GKaV）的基因片段，也就是诱发小牛病因子，可以在烟草露兰兰中诱导伴有异位木质化细胞和类木质化组织的瘤的形成。菖蒲小牛病相关病毒引发小牛病症状的分子机制将为植物病毒相互作用和调控维管和叶片发育的调控机制提供新的见解。

Plant viruses induce various disease symptoms that substantially impact agriculture, but the underlying mechanisms of viral disease in plants are poorly understood. Kobu-sho is a disease in gentian that shows gall formation with ectopic development of lignified cells and vascular tissues such as xylem. Here, we show that a gene fragment of gentian Kobu-sho-associated virus, which is designated as Kobu-sho-inducing factor (KOBU), induces gall formation accompanied by ectopic development of lignified cells and xylem-like tissue in Nicotiana benthamiana. Transgenic gentian expressing KOBU exhibited tumorous symptoms, confirming the gall-forming activity of KOBU. Surprisingly, KOBU expression can also induce differentiation of an additional leaf-like tissue on the abaxial side of veins in normal N. benthamiana and gentian leaves. Transcriptome analysis with Arabidopsis thaliana expressing KOBU revealed that KOBU activates signaling pathways that regulate xylem development. KOBU protein forms granules and plate-like structures and co-localizes with mRNA splicing factors within the nucleus. Our findings suggest that KOBU is a novel pleiotropic virulence factor that stimulates vascular and leaf development.IMPORTANCEWhile various mechanisms determine disease symptoms in plants depending on virus-host combinations, the details of how plant viruses induce symptoms remain largely unknown in most plant species. Kobu-sho is a disease in gentian that shows gall formation with ectopic development of lignified cells and vascular tissues such as xylem. Our findings demonstrate that a gene fragment of gentian Kobu-sho-associated virus (GKaV), which is designated as Kobu-sho-inducing factor, induces the gall formation accompanied by the ectopic development of lignified cells and xylem-like tissue in Nicotiana benthamiana. The molecular mechanism by which gentian Kobu-sho-associated virus induces the Kobu-sho symptoms will provide new insight into not only plant-virus interactions but also the regulatory mechanisms underlying vascular and leaf development.