Muro Keita, Yamasaki Arisa, Matsumoto Maki, Tanaka Yu-Ki, Ogra Yasumitsu, Fujiwara Toru, Yoshinari Akira, Takano Junpei
Graduate School of Agriculture, Osaka Metropolitan University, Osaka 599-8531, Japan.
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Osaka 599-8531, Japan.
Plant Physiol. 2025 Mar 28;197(4). doi: 10.1093/plphys/kiaf100.
Boron is an essential micronutrient required for plant cell wall integrity, as it is necessary for crosslinking the pectic polysaccharide rhamnogalacturonan II. Reproductive organs require a greater amount of boron for development and growth compared with vegetative organs. However, the mechanism by which plants distribute boron to specific organs is not fully understood. Under boron-limited conditions, the borate exporter BOR1 plays a central role in transporting boron from the roots to the shoots in Arabidopsis (Arabidopsis thaliana). Here, we found that BOR1 is expressed in the tapetal cells of young anthers in unopened buds, showing polar localization toward the locule where microspores develop. Tapetum-localized BOR1 undergoes endocytosis and is subsequently degraded during anther development. BOR1 degradation occurs independently of the lysine residue at Position 590 of BOR1, which is responsible for high boron-induced ubiquitination and degradation. Loss-of-function bor1 mutants exhibit disrupted pollen structure, causing reduced fertility under boron-sufficient conditions in the wild type. These phenotypes were rescued by supplementing with high boron concentrations. Furthermore, inflorescence stem grafting experiments suggested that BOR1-dependent boron transport in the flower is necessary for pollen development and subsequent fertilization under boron-sufficient conditions. Our findings suggest the borate exporter BOR1, together with the previously described boric acid channel NIP7;1, facilitates boron transport in tapetal cells toward the locule, thereby supporting pollen development in young anthers under boron-limited conditions.
硼是植物细胞壁完整性所必需的一种微量营养素，因为它对于果胶多糖鼠李半乳糖醛酸聚糖II的交联是必要的。与营养器官相比，生殖器官在发育和生长过程中需要更多的硼。然而，植物将硼分配到特定器官的机制尚未完全了解。在硼限制条件下，硼酸盐转运体BOR1在拟南芥中将硼从根部运输到地上部分发挥着核心作用。在这里，我们发现BOR1在未开放花蕾的幼嫩花药的绒毡层细胞中表达，向小孢子发育的药室呈极性定位。定位于绒毡层的BOR1会发生内吞作用，并在花药发育过程中随后被降解。BOR1的降解独立于BOR1第590位的赖氨酸残基发生，该残基负责高硼诱导的泛素化和降解。功能缺失的bor1突变体表现出花粉结构破坏，在野生型硼充足的条件下导致育性降低。通过补充高浓度硼可以挽救这些表型。此外，花序茎嫁接实验表明，在硼充足的条件下，花中依赖BOR1的硼运输对于花粉发育和随后的受精是必要的。我们的研究结果表明，硼酸盐转运体BOR1与先前描述的硼酸通道NIP7;1一起，促进硼在绒毡层细胞中向药室的运输，从而在硼限制条件下支持幼嫩花药中的花粉发育。
