Arabidopsis ICK/KRP cyclin-dependent kinase inhibitors function to ensure the formation of one megaspore mother cell and one functional megaspore per ovule

First author: Ling Cao; Affiliations: University of Saskatchewan (萨斯喀彻温大学): Saskatoon, Canada

Corresponding author: Hong Wang

In most plants, the female germline starts with the differentiation of one megaspore mother cell (MMC; 大孢子母细胞) in each ovule (胚珠) that produces four megaspores through meiosis, one of which survives to become the functional megaspore (FM; 功能大孢子). The FM further develops into an embryo sac (胚囊). Little is known regarding the control of MMC formation to one per ovule and the selective survival of the FM. The ICK/KRPs (interactor/inhibitor of cyclin-dependent kinase (CDK)/Kip-related proteins; 细胞周期蛋白依赖激酶CDK的抑制子ICKs或几枚抑制蛋白Kip相关蛋白KRPs) are plant CDK inhibitors and cell cycle regulators. Here we report that in the ovules of Arabidopsis mutant with all seven ICK/KRP genes inactivated, supernumerary (额外的) MMCs, FMs and embryo sacs were formed and the two embryo sacs could be fertilized to form two embryos with separate endosperm (胚乳) compartments. Twin seedlings (双苗) were observed in about 2% seeds. Further, in the mutant ovules the number and position of surviving megaspores from one MMC were variable, indicating that the positional signal for determining the survival of megaspore was affected. Strikingly, ICK4 fusion protein with yellow fluorescence protein was strongly present in the degenerative (退化的) megaspores but absent in the FM, suggesting an important role of ICKs in the degeneration of non-functional megaspores. The absence of or much weaker phenotypes in lower orders of mutants and complementation of the septuple mutant (七突) by ICK4 or ICK7 indicate that multiple ICK/KRPs function redundantly in restricting the formation of more than one MMC and in the selective survival of FM, which are critical to ensure the development of one embryo sac and one embryo per ovule.

在大多数的植物中，雌性植株的生殖系开始于胚珠中单个大孢子母细胞MMC的分化，其来源于减数分裂形成的4个一样的大孢子细胞，其中一个存活下来形成了功能性大孢子FM。FM会进一步发育成为胚囊。目前，关于单个胚珠中MMC的形成和FM的选择性存活的调控机制还了解得很少。细胞周期蛋白依赖激酶CDK的抑制子ICKs或几枚抑制蛋白Kip相关蛋白KRPs（ICK/KRPs）是一类植物细胞周期蛋白依赖激酶CDK的抑制子，同时也是细胞周期的调控子。本文报道了拟南芥7个ICK/KRP基因全都失活的突变体胚珠中形成了额外的MMC、FM以及胚囊，另外两个胚囊均可以受精形成两个胚，并能够形成各自的胚乳组织。2%的种子能够萌发出双苗。此外，在突变体胚珠中，存活下来的大孢子数量和位置存在变异，表明决定大孢子存活的位置信号受到了影响。有趣的事，ICK4与黄色荧光蛋白形成的融合蛋白在退化了的大孢子中强烈表达，而在FM中则检测不到，这显示ICK在非功能性的大孢子降解过程中扮演重要作用。比七突少的突变体中表型会缺失或者弱化，而ICK4或者ICK7基因能够互补七突的表型，这些结果表明不同ICK/KRPs在仅限单个MMC形成和FM的选择性存活方面存在功能冗余，这对于确保每个胚珠均发育形成一个胚囊和一个胚至关重要。

通讯：Hong Wang (https://medicine.usask.ca/profiles/biochemistry/hong-wang.php)

个人简历：华中农业大学，农艺学学士；不列颠哥伦比亚大学，植物科学硕士；萨斯喀彻温大学，生物学博士。

doi: https://doi.org/10.1371/journal.pgen.1007230

Journal: PLOS Genetics

Published date: 07 March, 2018

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