• The mechanisms underlying plant tolerance to boron (B) excess are far from fully understood. Here we characterized the role of the miR397-CsiLAC4/CsiLAC17 (from Citrus sinensis) module in regulation of B flow.
• Live-cell imaging techniques were used in localization studies. A tobacco transient expression system tested modulations of CsiLAC4 and CsiLAC17 by miR397. Transgenic Arabidopsis were generated to analyze the biological functions of CsiLAC4 and CsiLAC17. CsiLAC4’s role in xylem lignification was determined by mRNA hybridization and cytochemistry. In situ B distribution was analyzed by laser ablation inductively coupled plasma mass spectrometry.
• CsiLAC4 and CsiLAC17 are predominantly localized in the apoplast of tobacco epidermal cells. Overexpression of CsiLAC4 in Arabidopsis improves the plants’ tolerance to boric acid excess by triggering high-B-dependent lignification of the vascular system’s cell wall and reducing free B content in roots and shoots. In Citrus, CsiLAC4 is expressed explicitly in the xylem parenchyma and is modulated by B-responsive miR397. Upregulation of CsiLAC4 in Citrus results in lignification of the xylem cell walls, restricting B flow from xylem vessels to the phloem.
• CsiLAC4 contributes to plant tolerance to boric acid excess via high-B-dependent lignification of cell walls, which set up a ‘physical barrier’ preventing B flow.

中文翻译：

---

CsiLAC4 通过细胞壁的高硼依赖性木质化调节拟南芥和柑橘中的硼流动

• 植物对硼 (B) 过量的耐受性机制远未完全了解。在这里，我们描述了 miR397-CsiLAC4/CsiLAC17（来自Citrus sinensis）模块在 B 流量调节中的作用。
• 活细胞成像技术用于定位研究。烟草瞬时表达系统测试了 miR397 对 CsiLAC4 和 CsiLAC17 的调节。生成转基因拟南芥以分析 CsiLAC4 和 CsiLAC17 的生物学功能。CsiLAC4 在木质部木质化中的作用由 mRNA 杂交和细胞化学确定。通过激光烧蚀电感耦合等离子体质谱分析原位B 分布。
• CsiLAC4 和 CsiLAC17 主要定位于烟草表皮细胞的质外体。CsiLAC4在拟南芥中的过表达通过触发维管系统细胞壁的高 B 依赖性木质化和降低根和芽中的游离 B 含量来提高植物对硼酸过量的耐受性。在柑橘中，CsiLAC4在木质部实质中明确表达，并受 B 反应性 miR397 的调节。柑橘中CsiLAC4的上调导致木质部细胞壁的木质化，限制 B 从木质部血管到韧皮部的流动。
• CsiLAC4 通过细胞壁的高 B 依赖性木质化促进植物对硼酸过量的耐受性，从而建立了阻止 B 流动的“物理屏障”。