Mutation in Polycomb repressive complex 2 gene OsFIE2 promotes asexual embryo formation in rice.

Prevention of autonomous division of the egg apparatus and central cell in a female gametophyte before fertilization ensures successful reproduction in flowering plants. Here we show that rice ovules of Polycomb repressive complex 2 (PRC2) Osfie1 and Osfie2 double mutants exhibit asexual embryo and autonomous endosperm formation at a high frequency, while ovules of single Osfie2 mutants display asexual pre-embryo-like structures at a lower frequency without fertilization. Earlier onset, higher penetrance and better development of asexual embryos in the double mutants compared with those in Osfie2 suggest that the autonomous endosperm facilitated asexual embryo development.

Genomic diversity and evolution, diagnosis, prevention, and therapeutics of the pandemic COVID-19 disease.

The coronavirus disease 19 (COVID-19) is a highly transmittable and pathogenic viral infection caused by a novel evolutionarily divergent RNA virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus first emerged in Wuhan, China in December 2019, and subsequently spreaded around the world. Genomic analyses revealed that this zoonotic virus may be evolved naturally but not a purposefully manipulated laboratory construct.

Mutants in the imprinted PICKLE RELATED 2 gene suppress seed abortion of fertilization independent seed class mutants and paternal excess interploidy crosses in Arabidopsis.

Endosperm cellularization is essential for embryo development and viable seed formation. Loss of function of the FERTILIZATION INDEPENDENT SEED (FIS) class Polycomb genes, which mediate trimethylation of histone H3 lysine27 (H3K27me3), as well as imbalanced contributions of parental genomes interrupt this process. The causes of the failure of cellularization are poorly understood.

Developmentally regulated HEART STOPPER, a mitochondrially targeted L18 ribosomal protein gene, is required for cell division, differentiation, and seed development in Arabidopsis.

Evidence is presented for the role of a mitochondrial ribosomal (mitoribosomal) L18 protein in cell division, differentiation, and seed development after the characterization of a recessive mutant, heart stopper (hes). The hes mutant produced uncellularized endosperm and embryos arrested at the late globular stage. The mutant embryos differentiated partially on rescue medium with some forming callus.

Imprinting in plants and its underlying mechanisms.

Genomic imprinting (or imprinting) refers to an epigenetic phenomenon by which the allelic expression of a gene depends on the parent of origin. It has evolved independently in placental mammals and flowering plants. In plants, imprinting is mainly found in endosperm.

Transgene expression and transgene-induced silencing in diploid and autotetraploid Arabidopsis.

Previous studies have suggested that transgene expression in plants can be affected by ploidy. Here we show that three different transgenes, a reporter transgene, an antisense transgene, and a hairpin RNA (hpRNA) transgene, are all expressed at a lower level in autotetraploid (4n) than in diploid (2n) Arabidopsis. RNA silencing of two endogenous genes was induced by the antisense and hpRNA transgenes and this silencing is significantly less effective in 4n than in 2n Arabidopsis; furthermore, the reduced silencing in 4n Arabidopsis correlated with reduced accumulation of silencing-inducer RNAs.

The VQ motif protein IKU1 regulates endosperm growth and seed size in Arabidopsis.

Arabidopsis seed size is regulated by the IKU pathway that includes IKU2 (a leucine-rich repeat kinase) and MINI3 (a WRKY transcription factor). We report the cloning of the IKU1 (At2g35230) gene. iku1 mutants cause reduced endosperm growth and the production of small seeds.

Expression, imprinting, and evolution of rice homologs of the polycomb group genes.

Polycomb group proteins (PcG) play important roles in epigenetic regulation of gene expression. Some core PcG proteins, such as Enhancer of Zeste (E(z)), Suppressor of Zeste (12) (Su(z)12), and Extra Sex Combs (ESC), are conserved in plants. The rice genome contains two E(z)-like genes, OsiEZ1 and OsCLF, two homologs of Su(z)12, OsEMF2a and OsEMF2b, and two ESC-like genes, OsFIE1 and OsFIE2.

Parental memories shape seeds.

It is ten years since imprinting was first demonstrated in Arabidopsis, following the realization, five years earlier, that some genetic controls of seed development did not conform to Mendelian inheritance. Sixteen imprinted genes have since been identified in maize and Arabidopsis and these are expressed primarily in the endosperm, which nurtures embryo development. Imprinting results from the regulation of transcriptional silencing by DNA methylation or by Polycomb Group complex-mediated histone methylation.

UBIQUITIN-SPECIFIC PROTEASE 26 is required for seed development and the repression of PHERES1 in Arabidopsis.

The Arabidopsis mutant Atubp26 initiates autonomous endosperm at a frequency of approximately 1% in the absence of fertilization and develops arrested seeds at a frequency of approximately 65% when self-pollinated. These phenotypes are similar to those of the FERTILIZATION INDEPENDENT SEED (FIS) class mutants, mea, fis2, fie, and Atmsi1, which also show development of the central cell into endosperm in the absence of fertilization and arrest of the embryo following fertilization. Atubp26 results from a T-DNA insertion in the UBIQUITIN-SPECIFIC PROTEASE gene AtUBP26, which catalyzes deubiquitination of histone H2B and is required for heterochromatin silencing.

DNA methylation causes predominant maternal controls of plant embryo growth.

The parental conflict hypothesis predicts that the mother inhibits embryo growth counteracting growth enhancement by the father. In plants the DNA methyltransferase MET1 is a central regulator of parentally imprinted genes that affect seed growth. However the relation between the role of MET1 in imprinting and its control of seed size has remained unclear.

MINISEED3 (MINI3), a WRKY family gene, and HAIKU2 (IKU2), a leucine-rich repeat (LRR) KINASE gene, are regulators of seed size in Arabidopsis.

We have identified mutant alleles of two sporophytically acting genes, HAIKU2 (IKU2) and MINISEED3 (MINI3). Homozygotes of these alleles produce a small seed phenotype associated with reduced growth and early cellularization of the endosperm. This phenotype is similar to that described for another seed size gene, IKU1.

Genetic analysis of seed coat development in Arabidopsis.

In the angiosperms, fertilization initiates the formation of the seed from the ovule, including the differentiation of the seed coat from the ovule integuments. Seed coat differentiation includes some of the most dramatic cellular changes of seed development and culminates in the death of the seed coat cells. Recently, genetic analyses in Arabidopsis have contributed substantially to our understanding of many aspects of seed coat biology and it might not be long before the entire differentiation pathway is understood.

Plant genetics: hothead healer and extragenomic information.

Lolle et al. suggest that non-mendelian inheritance in Arabidopsis thaliana might be attributable to an ancestral RNA-sequence cache, whereby the RNA genome of previous generations causes a high rate of reversion of the plant's mutant hothead (hth) and erecta (er) genes. Here I describe a 'distributed genome' model that also explains their results, in which mutant hth DNA is restored by homologous sequences present in the genome itself.

Genetic and epigenetic processes in seed development.

Seed development has emerged as an important area of research in plant development. Recent research has highlighted the divergent reproductive strategies of the male and female genomes and interaction between genetic and epigenetic control mechanisms. Isolation of genes involved in embryo and endosperm development is leading to an understanding of the regulation of these processes at the molecular level.