Ogawa Satoshi, Wakatake Takanori, Spallek Thomas, Ishida Juliane K, Sano Ryosuke, Kurata Tetsuya, Demura Taku, Yoshida Satoko, Ichihashi Yasunori, Schaller Andreas, Shirasu Ken
RIKEN Center for Sustainable Resource Science, Yokohama 230-0045, Japan.
Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan.
Plant Physiol. 2021 Apr 23;185(4):1381-1394. doi: 10.1093/plphys/kiaa001.
Parasitic plants that infect crops are devastating to agriculture throughout the world. These parasites develop a unique inducible organ called the haustorium that connects the vascular systems of the parasite and host to establish a flow of water and nutrients. Upon contact with the host, the haustorial epidermal cells at the interface with the host differentiate into specific cells called intrusive cells that grow endophytically toward the host vasculature. Following this, some of the intrusive cells re-differentiate to form a xylem bridge (XB) that connects the vasculatures of the parasite and host. Despite the prominent role of intrusive cells in host infection, the molecular mechanisms mediating parasitism in the intrusive cells remain poorly understood. In this study, we investigated differential gene expression in the intrusive cells of the facultative parasite Phtheirospermum japonicum in the family Orobanchaceae by RNA-sequencing of laser-microdissected haustoria. We then used promoter analyses to identify genes that are specifically induced in intrusive cells, and promoter fusions with genes encoding fluorescent proteins to develop intrusive cell-specific markers. Four of the identified intrusive cell-specific genes encode subtilisin-like serine proteases (SBTs), whose biological functions in parasitic plants are unknown. Expression of SBT inhibitors in intrusive cells inhibited both intrusive cell and XB development and reduced auxin response levels adjacent to the area of XB development. Therefore, we propose that subtilase activity plays an important role in haustorium development in P. japonicum.
感染农作物的寄生植物对全球农业造成了毁灭性影响。这些寄生虫会发育出一种独特的可诱导器官，称为吸器，它连接寄生虫和宿主的维管系统，以建立水和养分的流动。与宿主接触后，吸器与宿主界面处的表皮细胞会分化为特定的细胞，称为侵入细胞，这些细胞向内生长朝向宿主维管系统。在此之后，一些侵入细胞会重新分化形成连接寄生虫和宿主维管系统的木质部桥（XB）。尽管侵入细胞在宿主感染中起着重要作用，但介导侵入细胞寄生的分子机制仍知之甚少。在本研究中，我们通过对激光显微切割的吸器进行RNA测序，研究了列当科兼性寄生植物日本地黄侵入细胞中的差异基因表达。然后，我们利用启动子分析来鉴定在侵入细胞中特异性诱导的基因，并将启动子与编码荧光蛋白的基因融合，以开发侵入细胞特异性标记。鉴定出的四个侵入细胞特异性基因编码枯草杆菌蛋白酶样丝氨酸蛋白酶（SBT），其在寄生植物中的生物学功能尚不清楚。在侵入细胞中表达SBT抑制剂可抑制侵入细胞和XB的发育，并降低XB发育区域附近的生长素反应水平。因此，我们认为枯草杆菌蛋白酶活性在日本地黄吸器发育中起着重要作用。
