In flowering plants (angiosperms), fertilization of the egg cell by one sperm cell produces an em-bryo, whereas fusion of a second sperm cell with the central cell generates the endosperm. In most angiosperms like Arabidopsis, a pollen grain con-tains two isomorphic sperm cells required for this double fertilization process. A long-standing un-solved question is whether the two fertilization events have any preference. A tool to address this question is the usage of the cyclin-dependent kinase a1 (cdka;1) mutant pollen, which produces a single sperm-like cell (SLC). Here, we first adopt a complementation-based fluorescence-labeling method to successfully separate and collect cdka;1 mutant pollen containing a single SLC. Single-cell RNA-sequencing analysis revealed that cdka;1 SLCs show a gene expression profile highly similar to that of sperm cells and not to the generative cell, precursor of the two sperm cells. Pollination assays using a limited number of cdka;1 mutant pollen revealed that in 98.2％of the ovules, single fertilization of the egg cell occurred. Pollination of pistils with excessive cdka;1 mutant pollen allowed the delivery of a second SLC via fertilization recovery, which fertilized the central cell, resulting in 20.7％ double-fertilized ovules. This indicates that cdka;1 SLCs are able to fertilize both the egg and the central cell. Taken together, our findings have answered a long-standing question and support that preferential fertiliza-tion of the egg cell is evident in Arabidopsis.

Ling Li;Saiying Hou;Wei Xiang;Zihan Song;Yuan Wang;Li Zhang;Jing Li;Hongya Gu;Juan Dong;Thomas Dresselhaus;Sheng Zhong;Li-Jia Qu

State Key Laboratory for Protein and Plant Gene Research,Peking-Tsinghua Center for Life Sciences at College of Life Sciences,Peking University,Beijing 100871,China;Beijing Advanced Innovation Center for Tree Breeding by Molecular Design,College of Bioscience and Resources Environment,Beijing University of Agriculture,Beijing 102206,China;The National Plant Gene Research Center,Beijing 100101,China;The Waksman Institute of Microbiology,Rutgers the State University of New Jersey,Piscataway,NJ"2"08854,USA;Cell Biology and Plant Biochemistry,University of Regensburg,Regensburg 93053,Germany

植物学报（英文版）

[1]Ling Li;Saiying Hou;Wei Xiang;Zihan Song;Yuan Wang;Li Zhang;Jing Li;Hongya Gu;Juan Dong;Thomas Dresselhaus;Sheng Zhong;Li-Jia Qu-.The egg cell is preferentially fertilized in Arabidopsis double fertilization FA)[J].植物学报（英文版）,2022(11):2039-2046

bryo,cdka,pistils,fertiliza

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