In order to reduce the chromosome number by half before the formation of gametes, meiocytes undergo a complicated process in which one round of chromosome replication is followed by two rounds of cell division.During meiosis, sister chromatid cohesion should be released in two steps. The first step is along chromosome arms during meiosis I and the second is around the centromeres during meiosis II. Therefore, the cohesin in the vicinity of the centromere must be retained until anaphase II to maintain the fidelity of chromosome segregation. Shugoshins are the conserved proteins required for protecting the cohesin adjacent to the centromeres from cleavage by the separase. Shugoshins have been identified in various organisms from yeast to humans.

Dr. Zhukuan Cheng’s group from Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, identified the rice shugoshin protein OsSGO1. They found that during both mitosis and meiosis, OsSGO1 was recruited from nucleoli onto centromeres at the onset of prophase. In the Tos17-insertional Ossgo1 mutant, centromeres of sister chromatids separated precociously from each other from metaphase I, which caused unequal chromosome segregation during meiosis II. Moreover, the release of OsSGO1 from nucleoli was completely blocked in Ossgo1, which leaded to the absence of OsSGO1 in centromeric regions after the onset of mitosis and meiosis. Furthermore, the timely assembly and maintenance of synaptonemal complexes during early prophase I were affected in Ossgo1 mutants, implied the new function of plant shugoshin in prophase I.

Identification and characterization of OsSGO1 improved our understanding about the regulating mechanism of homologous chromosome segregation in plant meiosis. This work has been online published on the Plant Journal （DOI: 10.1111/j.1365-313X.2011.04615.x）on April 19, 2011. Mo Wang in Dr. Zhukuan Cheng’s laboratory is the first author.This work was supported by grants from the Ministry of Sciences and Technology of China, and the National Natural Science Foundation of China.

AUTHOR CONTACT:

Cheng Zhukuan, Ph.D.

Institute of Genetics and Developmetnal Biology, Chinese Academy of Sciences, Beijing, China.

E-mail: zkcheng@genetics.ac.cn