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LIU Chunming's group deciphered the machiney underling the zygote activation in plants
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Zygote activation is the critical event of starting a new life in both plants and animals. Through double fertilization, two sperm cells delivered by the pollen tube fuse with the egg and the central cell, to produce an embryo and an endosperm, respectively. Although many genes involved in zygotic embryogenesis have been identified in plants, the mechanism underlying zygote activation in plants is largely unknown. Recently, through genetic analyses of zygote-arrest mutants, LIU Chunming's group discovered that ZYGOTE-ARREST 1 (ZYG1) gene that encodes the APC11 subunit of the anaphase promoting complex/cyclosome (APC/C) is critical for the initiation of the zygote division. ZYG1 is primarily expressed in mitosis-active tissues such as embryo, endosperm, root and shoot apical meristems. Mutation of ZYG1 led to zygote-lethal and CYCB1-GUS over-accumulation phenotypes. Biochemical studies revealed that ZYG1, together with E1 and E2, constitutes an active E3 ligase that is able to ubiquitinate CYCB1;1, leading to the degradation of the CYCB1;1. Expression of CYCB1;1 with a mutated D-box under an embryo-specific promoter also showed zygote-lethal phenotype similar to zyg1. It was also showed that mutations of several other APC subunits led to zygote lethal phenotype as well. These results demonstrated that APC/C initiates zygote activation in plants through promoting CYCB1;1 degradation. This work is published in Plant Journal on April 6th, 2016. Two PhD students, GUO Lei and JIANG Li, are co-first authored the paper. This study was supported by grants from the National Basic Research Program of China, and the Sino-Dutch International Collaboration Project.

Figure. (a) An embryo from wild type. (b) An arrested zygote from zyg1 mutant. (c) CYCB1-GUS was over-accumulated in aborted ovules of a ZYG1/zyg1 silique. (d) The differential ratios of ovules accumulating CYCB1-GUS from the wildtype or ZYG1/zyg1 plants. (e) and (f) GUS staining of ovules from wildtype or ZYG1/zyg1 transgenic plants with CYCB1-GUS.
Contact Info:
Prof. LIU Chunming
The Key Laboratory of Plant Molecular Physiology
Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China

Institute of Botany, CAS    Add: No.20 Nanxincun, Xiangshan, Beijing 100093, China
Tel: +86 10 6283 6215    Fax: +86 10 6259 0833    E-mail: lengjing@ibcas.ac.cn