Heat shock-induced failure of meiosis I to meiosis II transition leads to 2n pollen formation in a woody plant

第一作者：Qing Zhou

第一单位：北京林业大学

通讯作者：Pingdong Zhang

 Abstarct 

背景回顾：The formation of diploid gametes through chromosome doubling is a major mechanism of polyploidization, diversification, and speciation in plants. Unfavorable climate conditions can induce or stimulate the production of diploid gametes during meiosis. 

通过染色体加倍形成二倍体配子是植物多倍体化、多样化以及物种形成的主要机制。不利的气候条件可以诱导或刺激减数分裂过程中二倍体配子的产生。

结果1-热激促进2n花粉形成：Here, we demonstrated that heat shock stress (38 °C for 3 or 6 h) induced 2n pollen formation, and we generated 42 triploids derived from heat-shock-induced 2n pollen of Populus canescens. Meiotic analysis of treated pollen mother cells (PMCs) revealed that induced 2n pollen originated from the complete loss of meiosis II (MII). Among the 42 triploids, 38 triploids derived from SDR-type 2n pollen and 4 triploids derived from FDR-type 2n pollen were verified using SSR molecular markers. 

本文中，作者证实了持续3小时或者6小时的38 °C 热激胁迫能够诱导2n花粉的形成，并利用热激诱导的银灰杨2n花粉进行授粉，获得了42株三倍体杨树。对处理后的花粉母细胞（PMCs）进行减数分裂分析，发现热激介导的2n花粉源自于减数分裂II的完全丧失。在42个三倍体中，利用SSR分子标记证实了38个来自SDR型2n花粉，另外4个来自FDR型2n花粉。

结果2-关键基因鉴定：Twenty-two differentially expressed genes related to the cell cycle were identified and characterized by expression profile analysis. Among them was POPTR_0002s08020g (PtCYCA1;2), which encodes a type A Cyclin CYCA1;2 that is required for the MI to MII transition. After male flower buds were exposed to heat shock, a significant reduction was detected in PtCYCA1;2 expression. We inferred that the failure of MI-to-MII transitions might be associated with downregulated expression of PtCYCA1;2, leading to the formation of SDR-type 2n pollen. 

通过表达谱分析，作者鉴定了22个与细胞周期相关的差异表达基因。其中PtCYCA1;2基因编码A型细胞周期蛋白CYCA1;2介导减数分裂I期到减数分裂II期的转变。当雄花芽暴露于热冲击后，PtCYCA1;2基因的表达显著降低。因此，作者推测减数分裂I-II期的转变失败可能与PtCYCA1;2基因的表达下调有关，从而导致了SDR型2n花粉的形成。

结论：Our findings provide insights into mechanisms of heat-shock-induced 2n pollen formation in a woody plant and verify that sensitivity to environmental stress has evolutionary importance in terms of polyploidization.

本文的研究结果为木本植物热激诱导2n花粉形成的机制提供了深入的见解，并证实了植物对环境胁迫的敏感性在多倍体化方面具有演化上的重要性。

注：自然界中存在产生未减数配子的自发突变体，根据减数分裂突变发生的时期，产生未减数配子的减数分裂突变被分为“第一次分裂重组” (FDR, the first division restitution)和“第二次分裂重组” (SDR, the second division restitution)。

FDR：主要发生在减数第一次分裂后期，染色体的姐妹染色单体在减数第一次分裂后期即分开，形成2个染色体数目没有减数的重组核。到减数第二次分裂时，染色体不再分离，胞质进行一次分裂形成2个2n配子。

SDR：指性母细胞减数第一次分裂正常，但到减数第二次分裂时，姐妹染色单体分开后没有移向两极再分配到两个核中，而是包含在1个核内，形成与亲本体细胞染色体数目相同的重组核，再经胞质分裂形成二分体，由二分体发育成两个2n配子。

** 张平冬 **

doi: https://doi.org/10.1093/plphys/kiac219

Journal: Plant Physiology

Published date: May 14, 2022

CITE

Qing Zhou,  Xuetong Cheng,  Bo Kong,  Yifan Zhao,  Zhiqun Li,  Yaru Sang,  Jian Wu, Pingdong Zhang. Heat shock-induced failure of meiosis I to meiosis II transition leads to 2n pollen formation in a woody plant. Plant Physiology, 2022. DOI: https://doi.org/10.1093/plphys/kiac219​