State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences and School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China.
College of Life Sciences, Capital Normal University, Beijing 100048, China.
Dev Cell. 2019 Oct 7;51(1):78-88.e3. doi: 10.1016/j.devcel.2019.08.007. Epub 2019 Sep 5.
Apical hook curvature is crucial for buried seedling survival and a superb model for dissecting differential cell growth. HOOKLESS1 (HLS1) is essential for apical hook formation, acting as a hub integrating various external and internal signals. However, its functional mechanism remains unclear. Here, we demonstrate that HLS1 protein is present as an oligomer in the nucleus of dark-grown seedlings. Oligomerization is required for HLS1 activation, as the mutated HLS1 protein abolishing self-association exists as nonfunctional monomers. Upon light exposure, photoreceptor phyB translocates into the nucleus and interacts with HLS1, disrupting the self-association and oligomerization of HLS1 to initiate hook unfolding. Remarkably, genetic expression of nuclear-localized phyB is sufficient to inactivate HLS1, resulting in compromised hook curvature in etiolated seedlings. Together, we conclude that HLS1 protein is active as oligomeric form in darkness and achieves allosteric photo-deactivation upon light, providing intriguing mechanistic insight into the molecular switch for developmental transition.
顶端弯钩曲率对于埋地幼苗的生存至关重要，是解析细胞生长差异的理想模型。HOOKLESS1（HLS1）对于顶端弯钩的形成是必需的，作为一个整合各种外部和内部信号的枢纽。然而，其功能机制尚不清楚。在这里，我们证明 HLS1 蛋白以寡聚体的形式存在于黑暗生长的幼苗的细胞核中。寡聚化是 HLS1 激活所必需的，因为使自身缔合失活的突变 HLS1 蛋白以无功能的单体存在。暴露于光下时，光受体 phyB 易位到细胞核中并与 HLS1 相互作用，破坏 HLS1 的自缔合和寡聚化，从而启动弯钩展开。值得注意的是，核定位 phyB 的遗传表达足以使 HLS1 失活，导致黄化幼苗弯钩曲率受损。综上所述，我们得出结论，HLS1 蛋白在黑暗中以寡聚体的形式发挥作用，在光照下实现变构光失活，为发育转变的分子开关提供了有趣的机制见解。
