氏 名 ラフマン
エムディMDハッサヌール 学 位 の 種 類 博士（理学）
学 位 記 番 号 理工博 第
281号 学位授与の日付 平成
31年
3月
14日 課程・論文の別 学位規則第４条第１項該当
学 位 論 文 題 名
Temporal expression of genes from paternal alleles during early development of rice zygotes and involvement of OsASGR-BBML1 in initiation of zygotic developmentイネ受精卵初期発生過程における父性アリル依存的遺伝子発現およ
び
OsASGR-BBML1による受精卵の発生誘導（英文）
論 文 審 査 委 員 主査 教 授 岡本 龍史 委員 准教授 鐘ヶ江 健 委員 准教授 福田 公子
【論文の内容の要旨】
In angiosperms, after fusion of an egg cell with a sperm cell, initial development of the zygote progresses via egg activation, karyogamy, and de novo gene expression from zygotic nucleus, in which parental genome coexists, to promote faithful zygotic embryogenesis. Recent investigations for parentally imbalanced rice zygotes suggested that early developmental stages of zygotes are sensitive to an excess in paternal genome. Moreover, SNP-based mRNA-sequencing of intersubspecific rice zygotes was conducted, and twenty three genes expressing in zygotes with paternal allele-specific manner have been identified.
In the study, allele dependency of nine out of 23 genes in globular-like embryos were checked, and it was suggested that paternal allele dependent expression of the identified genes in zygotes are mostly converted into bi-allelic dependent manner in globular-like embryo. This suggests that paternal dependent expression of these genes is temporal event during early developmental stages of zygotes, and these gene products might function as paternally derived trigger for zygotic development. One of the identified genes, Oryza sativa apospory-specific genome region (ASGR)-BABY-BOOM LIKE (BBML)1 (OsASGR-BBML1), encoding AP2-type transcription factor, was further focused in the study, since it has been reported that ectopic expression of AP2-type transcription factors in somatic cells and egg cells induces somatic embryogenesis and apomixis, respectively. OsASGR-BBML1 expressed in sperm cells, zygotes and globular-like embryos but not in the egg cells. These suggest that OsASGR-BBML1 transcripts in early zygotes is derived from the sperm cells, and de novo
OsASGR-BBML1 expression occurs in developing zygotes in which activation of parental genome is
initiated. To address whether ectopic expression of OsASGR-BBML1 in egg cell induces the changes in cellular profiles of egg cells, plasmid vector containing OsASGR-BBML1 expression cassette (pOsASGR-BBML1) was delivered into rice egg cells by PEG-Ca2+-mediated transfection. This exogenous expression of OsASGR-BBML1 in egg cells induced fertilization-independent nuclear/cell division. Furthermore, pOsASGR-BBML1 was also delivered into rice zygotes to observe the effect of excess existence of OsASGR-BBML1 in zygotes on the zygotic development. The overexpression of the protein in zygotes provided inhibitory effect on progression of zygotic development. Taken together, it was suggested that expression level of OsASGR-BBML1 in egg cells and zygotes is suppressed and properly regulated, respectively, to maintain their cell fates. Monoallelic or preferential gene expressions from paternal genome in zygote might be a safety mechanism for egg cell to suppress the gene expression cascades toward embryogenesis that is triggered by fusion of egg cell with a sperm cell.
*Rahman MH, *Toda E, Kobayashi M, Kudo T, Takahara M, IwamiM, WatanabeY, SekimotoH, YanoK, Okamoto T Expression of genes from paternal allele in rice zygotes and involvement of OsASGR-BBML1 in initiation of zygotic development, Plant Cell Physiol., in press, * Equal contribution
