The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing, 100101, China.
University of the Chinese Academy of Sciences, Beijing, 100049, China.
J Integr Plant Biol. 2024 May;66(5):986-1006. doi: 10.1111/jipb.13584. Epub 2024 Jan 2.
Self-incompatibility (SI) is an intraspecific reproductive barrier widely present in angiosperms. The SI system with the broadest occurrence in angiosperms is based on an S-RNase linked to a cluster of multiple S-locus F-box (SLF) genes found in the Solanaceae, Plantaginaceae, Rosaceae, and Rutaceae. Recent studies reveal that non-self S-RNase is degraded by the Skip Cullin F-box (SCF)-mediated ubiquitin-proteasome system in a collaborative manner in Petunia, but how self-RNase functions largely remains mysterious. Here, we show that S-RNases form S-RNase condensates (SRCs) in the self-pollen tube cytoplasm through phase separation and the disruption of SRC formation breaks SI in self-incompatible Petunia hybrida. We further find that the pistil SI factors of a small asparagine-rich protein HT-B and thioredoxin h together with a reduced state of the pollen tube all promote the expansion of SRCs, which then sequester several actin-binding proteins, including the actin polymerization factor PhABRACL, the actin polymerization activity of which is reduced by S-RNase in vitro. Meanwhile, we find that S-RNase variants lacking condensation ability fail to recruit PhABRACL and are unable to induce actin foci formation required for pollen tube growth inhibition. Taken together, our results demonstrate that phase separation of S-RNase promotes SI response in P. hybrida, revealing a new mode of S-RNase action.
自交不亲和性（SI）是被子植物中广泛存在的种内生殖障碍。在被子植物中，发生最广泛的 SI 系统基于与多 S 座位 F-box（SLF）基因簇相连的 S-RNase，这些基因簇存在于茄科、车前科、蔷薇科和芸香科中。最近的研究表明，在矮牵牛中，非自体 S-RNase 通过 Skip Cullin F-box（SCF）介导的泛素-蛋白酶体系统协同降解，但自体 S-RNase 的功能仍很大程度上是神秘的。在这里，我们表明 S-RNases 通过相分离在自体花粉管细胞质中形成 S-RNase 凝聚物（SRCs），而 SRC 形成的破坏会打破自交不亲和的矮牵牛中的 SI。我们进一步发现，一个富含天冬酰胺的小蛋白 HT-B 和硫氧还蛋白 h 与花粉管的还原态一起作为柱头 SI 因子，促进 SRC 的扩展，然后将几个肌动蛋白结合蛋白隔离在内，包括肌动蛋白聚合因子 PhABRACL，其肌动蛋白聚合活性在体外被 S-RNase 降低。同时，我们发现缺乏凝聚能力的 S-RNase 变体无法招募 PhABRACL，并且无法诱导抑制花粉管生长所需的肌动蛋白焦点形成。总之，我们的结果表明，S-RNase 的相分离促进了矮牵牛中的 SI 反应，揭示了 S-RNase 作用的一种新模式。
