Expansins facilitate cell expansion via mediating pH-dependent cell wall (CW) loosening. However, the role of expansins in the control of biomechanical CW properties in the tissue and organ context remains elusive. We determined hormonal responsiveness and specificity of expression and localization of expansins predicted to be direct targets of cytokinin signalling. We found EXPA1 homogenously distributed throughout the CW of columella/ lateral root cap, while EXPA10 and EXPA14 localized predominantly at the three-cell boundaries of epidermis/cortex in various root zones. Cell type-specific localization of EXPA15 overlaps with higher CW stiffness measured via Brillouin light scattering microscopy. As indicated by both Brillouin frequency shift and AFM-measured Youngs modulus, EXPA1 overexpression upregulated CW stiffness, associated with shortening of the root apical meristem and root growth arrest. We propose that root growth in Arabidopsis requires delicate orchestration of biomechanical CW properties via tight regulation of various expansins localization to specific cell types and extracellular domains.

中文翻译：

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扩张素控制的细胞壁刚度调节拟南芥根的生长

扩展酶通过介导pH依赖性细胞壁（CW）松弛来促进细胞扩增。但是，在组织和器官环境中，expandins在控制生物力学CW特性方面的作用仍然难以捉摸。我们确定了激素反应性和表达的特异性，以及预测为细胞分裂素信号传导的直接靶标的扩展蛋白的定位。我们发现EXPA1均匀分布在整个小柱/侧根冠的CW中，而EXPA10和EXPA14主要位于表皮/皮层的三细胞边界的各个根区域中。通过布里渊光散射显微镜测得，EXPA15的细胞类型特异性定位与更高的CW刚度重叠。正如布里渊频移和AFM测量的杨氏模量所表明的，EXPA1过表达上调了CW刚度，与根尖分生组织缩短和根生长停滞有关。我们提出，拟南芥的根生长需要通过严格调节各种弹性蛋白定位于特定细胞类型和细胞外结构域的生物力学连续波特性的精细协调。