LLG2/3 Are Co-receptors in BUPS/ANX-RALF Signaling to Regulate Arabidopsis Pollen Tube Integrity
LLG2/3 Are Co-receptors in BUPS/ANX-RALF Signaling to Regulate Arabidopsis Pollen Tube Integrity
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DOI：
10.1016/j.cub.2019.08.032
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发表时间：
2019-10-07
期刊：
影响因子：
9.2
通讯作者：
Qu, Li-Jia
中科院分区：
文献类型：
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作者：
Ge, Zengxiang;Zhao, Yuling;Qu, Li-Jia
在被子植物中，两个精细胞通过花粉管运输并传递到胚珠，实现双受精。在花粉管和雌性组织之间进行广泛的交流，直到精细胞货物最终被释放。在这一过程中，由ANXUR 1/2（ANX 1/2）和Buddha's Paper Seal 1/2（BUPS 1/2）组成的花粉管表面受体复合物通过感知自分泌肽配体快速碱化因子4和19（RALF 4/19）来控制花粉管完整性的维持。进一步假设，花粉管破裂释放精子是由来自胚珠的旁分泌RALF 34肽干扰该信号传导途径引起的。在这项研究中，我们确定了两个拟南芥花粉管表达的糖基磷脂酰肌醇锚定蛋白（GPI-AP），LORELEI样GPIanchored蛋白2（LLG 2）和LLG 3，作为BUPS-ANX受体复合物的共受体。11 g2 - 11 g3双突变体表现出严重的育性缺陷。突变体花粉管在授粉过程中提前破裂。此外，LLG 2和LLG 3与BUPS和ANXUR的胞外域相互作用，并且这种相互作用通过RALF 4/19肽的存在而显著增强。我们进一步证明了RALF 4肽配体的N末端（包括YISY基序）与BUPSANX受体强烈相互作用，但与LLG弱相互作用，并且对于其生物学功能是必需的，并且其C末端区域足以用于LLG结合。总之，我们建议LLG 2/3作为共受体在BUPS/ ANX-RALF信号转导，从而进一步建立GPI-AP作为植物繁殖过程中的关键调节器的重要性。
In angiosperms, two spermcells are transported and delivered by the pollen tube to the ovule to achieve double fertilization. Extensive communication takes place between the pollen tube and the female tissues until the sperm cell cargo is ultimately released. During this process, a pollen tube surface-located receptor complex composed of ANXUR1/2 (ANX1/2) and Buddha's Paper Seal 1/2 (BUPS1/2) was reported to control the maintenance of pollen tube integrity by perceiving the autocrine peptide ligands rapid alkalinization factor 4 and 19 (RALF4/19). It was further hypothesized that pollen-tube rupture to release sperm is caused by the paracrine RALF34 peptide from the ovule interfering with this signaling pathway. In this study, we identified two Arabidopsis pollen-tube-expressed glycosylphosphatidylinositol-anchored proteins (GPI-APs), LORELEI-like-GPIanchored protein 2 (LLG2) and LLG3, as co-receptors in the BUPS-ANX receptor complex. llg2 llg3 double mutants exhibit severe fertility defects. Mutant pollen tubes rupture early during the pollination process. Furthermore, LLG2 and LLG3 interact with ectodomains of both BUPSs and ANXURs, and this interaction is remarkably enhanced by the presence of RALF4/19 peptides. We further demonstrate that the N terminus (including a YISY motif) of the RALF4 peptide ligand interacts strongly with BUPSANX receptors but weakly with LLGs and is essential for its biological function, and its C-terminal region is sufficient for LLG binding. In conclusion, we propose that LLG2/3 serve as co-receptors during BUPS/ ANX-RALF signaling and thereby further establish the importance of GPI-APs as key regulators in plant reproduction processes.