'Sapienza' University of Rome, Dept. of Environmental Biology, Rome, Italy.
J Exp Bot. 2012 Jan;63(1):471-88. doi: 10.1093/jxb/err295. Epub 2011 Oct 5.
The genetic basis of stem cell specification in somatic embryogenesis and organogenesis is still obscure. SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) genes are involved in embryogenesis and organogenesis in numerous species. In vitro culture of Cyclamen persicum immature ovules provides a system for investigating stem cell formation and maintenance, because lines forming either organs or embryos or callus without organs/embryos are available for the same cultivar and plant growth regulator conditions. The present aim was to exploit this property of cyclamen cultures to understand the role of SERK(s) in stem cell formation and maintenance in somatic embryogenesis and organogenesis in vitro, in comparison with expression in planta. CpSERK1 and CpSERK2 were isolated from embryogenic callus. CpSERK1 and CpSERK2 levels by RT-PCR showed that expression is high in embryogenic, moderate in organogenic, and null in recalcitrant calli. in situ hybridizations showed that the expression of both genes started in clumps of pluripotent stem cells, from which both pre-embryogenic aggregates and organ meristemoids derived, and continued in their trans-amplifying, meristem-like, derivatives. Expression declined in organ meristemoids, in parallel with a partial loss of meristematization. In mature somatic embryos, and in shoot and root primordia, CpSERK1 and CpSERK2 were expressed in meristems, and similar patterns occurred in zygotic embryo and primary meristems in planta. The results point to SERK1 and SERK2 as markers of pluripotency in cyclamen. It is proposed that the high expression of these genes in the trans-amplifying derivatives of the stem cells maintains a pluripotent condition leading to totipotency and, consequently, somatic embryogenesis.
体细胞胚胎发生和器官发生中干细胞特化的遗传基础仍然不清楚。SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) 基因参与了许多物种的胚胎发生和器官发生。在体外培养仙客来未成熟的胚珠提供了一个研究干细胞形成和维持的系统，因为同一品种和植物生长调节剂条件下，有形成器官或胚胎或无器官/胚胎愈伤组织的细胞系。本研究旨在利用仙客来培养物的这一特性，了解 SERK 在体外体细胞胚胎发生和器官发生中干细胞形成和维持中的作用，与体内的表达进行比较。从胚胎发生的愈伤组织中分离出 CpSERK1 和 CpSERK2。通过 RT-PCR 显示 CpSERK1 和 CpSERK2 的表达水平在胚胎发生中较高，在器官发生中中等，在顽固的愈伤组织中为零。原位杂交显示，这两个基因的表达都始于多能干细胞的团块，这些团块来自于预胚胎发生的聚集体和器官分生组织原，并且在它们的扩增、分生组织样的衍生物中继续表达。在器官分生组织原中，表达下降，与分生组织化的部分丧失平行。在成熟的体细胞胚以及茎和根原基中，CpSERK1 和 CpSERK2 在分生组织中表达，在体内的合子胚胎和初级分生组织中也出现了类似的模式。这些结果表明 SERK1 和 SERK2 是仙客来多能性的标志物。据推测，这些基因在干细胞的扩增衍生物中的高表达维持了多能性条件，导致全能性，进而导致体细胞胚胎发生。
