Tsugeki R, Fedoroff N V
Life Sciences Consortium and Biotechnology Institute, Wartik Laboratory, Pennsylvania State University, University Park, PA 16802, USA.
Proc Natl Acad Sci U S A. 1999 Oct 26;96(22):12941-6. doi: 10.1073/pnas.96.22.12941.
The root cap is increasingly appreciated as a complex and dynamic plant organ. Root caps sense and transmit environmental signals, synthesize and secrete small molecules and macromolecules, and in some species shed metabolically active cells. However, it is not known whether root caps are essential for normal shoot and root development. We report the identification of a root cap-specific promoter and describe its use to genetically ablate root caps by directing root cap-specific expression of a diphtheria toxin A-chain gene. Transgenic toxin-expressing plants are viable and have normal aerial parts but agravitropic roots, implying loss of root cap function. Several cell layers are missing from the transgenic root caps, and the remaining cells are abnormal. Although the radial organization of the roots is normal in toxin-expressing plants, the root tips have fewer cytoplasmically dense cells than do wild-type root tips, suggesting that root meristematic activity is lower in transgenic than in wild-type plants. The roots of transgenic plants have more lateral roots and these are, in turn, more highly branched than those of wild-type plants. Thus, root cap ablation alters root architecture both by inhibiting root meristematic activity and by stimulating lateral root initiation. These observations imply that the root caps contain essential components of the signaling system that determines root architecture.
根冠作为一个复杂且动态的植物器官，越来越受到重视。根冠感知并传递环境信号，合成并分泌小分子和大分子，在某些物种中还会脱落代谢活跃的细胞。然而，根冠对于地上部分和根系的正常发育是否必不可少尚不清楚。我们报告了一种根冠特异性启动子的鉴定，并描述了其通过指导白喉毒素A链基因在根冠中的特异性表达来对根冠进行基因消融的用途。表达毒素的转基因植物能够存活，地上部分正常，但根系失去向重力性，这意味着根冠功能丧失。转基因根冠中缺少几层细胞，剩余的细胞也不正常。尽管在表达毒素的植物中根系的径向组织正常，但根尖中细胞质致密的细胞比野生型根尖中的少，这表明转基因植物中的根分生组织活性低于野生型植物。转基因植物的根系有更多侧根，并且这些侧根比野生型植物的侧根分支更多。因此，根冠消融通过抑制根分生组织活性和刺激侧根起始来改变根系结构。这些观察结果表明，根冠包含决定根系结构的信号系统的关键成分。
