OsFIE2 plays an essential role in the regulation of rice vegetative and reproductive development

Abstract

Summary Polycomb group (PcG) proteins are gene repressors that help to maintain cellular identity during development via chromatin remodeling. Fertilization‐independent endosperm (FIE), a member of the PcG complex, operates extensively in plant development, but its role in rice has not been fully investigated to date. We report the isolation and characterization of a PcG member in rice, which was designated OsFIE2 for Oryza sativa Fertilization‐Independent Endosperm 2. OsFIE2 is a single‐copy gene in the rice genome and shows a universal expression pattern. The OsFIE2 RNAi lines displayed pleiotropic phenotypes in vegetative and reproductive organ generation. In unfertilized lines, endosperm formation could be triggered without embryo formation, which indicates that FIE is indeed involved in the suppression of autonomous endosperm development in rice. Furthermore, lateral root generation was promoted early in the roots of OsFIE2 RNAi lines, whereas the primary root was premature and highly differentiated. As the root tip stem cell differentiated, QHB, the gene required for stem cell maintenance in the quiescent center, was down‐regulated. Our data suggest that the OsFIE2–PcG complex is vital for rice reproduction and endosperm formation. Its role in stem cell maintenance suggests that the gene is functionally conserved in plants as well as animals.

Parental Genome Imbalance Causes Post-Zygotic Seed Lethality and Deregulates Imprinting in Rice

“…This is consistent with the role of H3K27me in rice endosperm development as knocking-down of OsFIE2 by RNAi results in abnormal endosperm development lacking of cellularization (Nallamilli et al 2013; Li et al 2014. Conversely, the elevated expression of OsFIE2 and slight down-regulation of OsMET1b were observed in the maternal excess cross, in which endosperm precociously cellularized.…”

“…We investigated the expression levels of OsFIE2 and OsMET1b , two major epigenetic modification genes showing function seed development (Luo et al 2009; Yamauchi et al 2009; Nallamilli et al 2013; Hu et al 2014; Li et al 2014) in the endosperm derived from the interploidy crosses and the parents Nip2n, TH4n and H2n (Fig. 3).…”

“…The rice genome contains two FERTILISATION INDEPENDENT ENDOSPERM ( FIE ) genes encoding members of the PRC2 complex (Luo et al 2009; Nallamilli et al 2013; Li et al 2014) and two MET1 genes (Yamauchi et al 2009; Hu et al 2014). OsFIE2 and OsMET1b are the major genes potentially regulating endosperm development and other processes (Luo et al 2009; Yamauchi et al 2009; Nallamilli et al 2013; Hu et al 2014; Li et al 2014).…”

“…OsFIE2 and OsMET1b are the major genes potentially regulating endosperm development and other processes (Luo et al 2009; Yamauchi et al 2009; Nallamilli et al 2013; Hu et al 2014; Li et al 2014). Given that PRC2 and MET1 are required for establishing postzygotic hybridization barrier via controlling imprinted genes in Arabidopsis (Erilova et al 2009; Kradolfer et al 2013a; Schatlowski et al 2014) and differential expression of imprinted genes between parental genomes in rice are likely controlled by differential H3K27me and DNA methylation (Rodrigues et al 2013; Du et al 2014), it is interesting to know if the rice PRC2 and MET1 counterparts have the same functions in regulating postzygotic hybridization barrier as in Arabidopsis, and whether loss of imprinting also occurs in the rice endosperm with parental genome imbalance.…”

Concerted Divergence after Gene Duplication in Polycomb Repressive Complexes

“…Thus, if there is a PRC2 complex regulating seed development in asterids, it probably contains the product of lineage-specific polycomb proteins and a mechanism independently evolved from Brassicaceae. In maize (Zea mays) and rice (Oryza sativa), there has been duplication of FIE (Luo et al, 2009;Li et al, 2014). Thus, the grasses may have PRC2 complexes that are divergent from the ancestral state.…”