Abstract:Anther and pollen development are crucial processes of plant male reproduction. Although a number of genes involved in these processes have been identified, the regulatory networks of pollen and anther development are still unclear. EMBRYONIC FLOWER 2b (OsEMF2b) is important for rice development. Its biological function in floral organ, flowering time and meristem determinacy have been well-studied, but its role, if only, on male reproduction is still unknown, because null mutants of OsEMF2b barely have anther… Show more
“…The vegetative growth of osemf2a-1 and osemf2a-2 was not significantly affected, but the heading date was somewhat delayed in the mutants ( Figure 1 B). Notably, we did not observe floral defects or sterility in osemf2a ( Figure 1 C) as in osemf2b ( Deng et al., 2017 ). Figure 1 Phenotype of the osemf2a mutants.…”
Section: Resultsmentioning
confidence: 53%
“…The two Su(z)12-group PRC2 members of rice are OsEMF2a and OsEMF2b ( Luo et al., 2009 ), which likely evolved from an ancient duplication event before the origin of the family Poaceae ( Supplemental Figure 1 A). Previous studies reported that the osemf2b mutant displayed abnormal floral organs, reduced pollen fertility, and decreased dormancy ( Xie et al., 2015 ; Chen et al., 2017 ; Deng et al., 2017 ; Zhong et al., 2018 ). However, we did not identify floral development and fertility issues in osemf2a ( Figure 1 C and 1I).…”
Cellularization is a key event in endosperm development. Polycomb group (PcG) genes, such as
Fertilization-Independent Seed 2
(
FIS2
), are vital for the syncytium-to-cellularization transition in
Arabidopsis
plants. In this study, we found that
OsEMF2a
, a rice homolog of the
Arabidopsis
PcG gene
Embryonic Flower2
(
EMF2
), plays aĀ role similar to that of
FIS2
in regard to seed development, although there is limited sequence similarity between the genes. Delayed cellularization was observed in
osemf2a
, associated with an unusual activation of type I MADS-box genes. The cell cycle was persistently activated in
osemf2a
caryopses, which was likely caused by cytokinin overproduction. However, the overaccumulation of auxin was not found to be associated with the delayed cellularization. As
OsEMF2a
is a maternally expressed gene in the endosperm, a paternally inherited functional allele was unable to recover the maternal defects of
OsEMF2a
. Many imprinted rice genes were deregulated in the defective hybrid seeds of
osemf2a
(ā)/9311 (ā) (m9). The paternal expression bias of some paternally expressed genes was disrupted in m9Ā due to either the activation of maternal alleles or the repression of paternal alleles. These findings suggest that OsEMF2a-PRC2-mediated H3K27me3 is necessary forĀ endosperm cellularization and genomic imprinting in rice.
“…The vegetative growth of osemf2a-1 and osemf2a-2 was not significantly affected, but the heading date was somewhat delayed in the mutants ( Figure 1 B). Notably, we did not observe floral defects or sterility in osemf2a ( Figure 1 C) as in osemf2b ( Deng et al., 2017 ). Figure 1 Phenotype of the osemf2a mutants.…”
Section: Resultsmentioning
confidence: 53%
“…The two Su(z)12-group PRC2 members of rice are OsEMF2a and OsEMF2b ( Luo et al., 2009 ), which likely evolved from an ancient duplication event before the origin of the family Poaceae ( Supplemental Figure 1 A). Previous studies reported that the osemf2b mutant displayed abnormal floral organs, reduced pollen fertility, and decreased dormancy ( Xie et al., 2015 ; Chen et al., 2017 ; Deng et al., 2017 ; Zhong et al., 2018 ). However, we did not identify floral development and fertility issues in osemf2a ( Figure 1 C and 1I).…”
Cellularization is a key event in endosperm development. Polycomb group (PcG) genes, such as
Fertilization-Independent Seed 2
(
FIS2
), are vital for the syncytium-to-cellularization transition in
Arabidopsis
plants. In this study, we found that
OsEMF2a
, a rice homolog of the
Arabidopsis
PcG gene
Embryonic Flower2
(
EMF2
), plays aĀ role similar to that of
FIS2
in regard to seed development, although there is limited sequence similarity between the genes. Delayed cellularization was observed in
osemf2a
, associated with an unusual activation of type I MADS-box genes. The cell cycle was persistently activated in
osemf2a
caryopses, which was likely caused by cytokinin overproduction. However, the overaccumulation of auxin was not found to be associated with the delayed cellularization. As
OsEMF2a
is a maternally expressed gene in the endosperm, a paternally inherited functional allele was unable to recover the maternal defects of
OsEMF2a
. Many imprinted rice genes were deregulated in the defective hybrid seeds of
osemf2a
(ā)/9311 (ā) (m9). The paternal expression bias of some paternally expressed genes was disrupted in m9Ā due to either the activation of maternal alleles or the repression of paternal alleles. These findings suggest that OsEMF2a-PRC2-mediated H3K27me3 is necessary forĀ endosperm cellularization and genomic imprinting in rice.
“…H3.3 variants correlate with gene expression in Arabidopsis , while H3.1 variants are incorporated during the S-phase of the cell cycle (Borg and Berger, 2015), and references therein). In rice, EMF2 function is essential for pollen development, and it is thought to interact with a rice MSI1 homolog, PTC1 (Deng et al, 2017). Genes encoding homologs of a number of these PRC2 components were also expressed in cowpea pollen development and may have comparable roles.…”
Molecular knowledge of pathways regulating seed formation in legumes, remains scarce. Thirteen isolated cell-type transcriptomes were developed, spanning temporal events of male and female gametogenesis and seed initiation, to examine pathways involved in cowpea seed formation. In situ hybridization confirmed localization of in silico identified cell-specific genes, verifying transcriptome utility. Cowpea and Arabidopsis reproductive cells showed some conservation in regulators enabling cell-type expression as some cowpea cell-specific genes promoters and their Arabidopsis homologs directed expression to identical reproductive cell-types in transgenic plants. In silico analyses revealed gene expression similarities and differences with genes in pathways regulating reproductive events in other plants. Meiosis-related genes were expressed at mitotic stages of gametogenesis and during sporophytic development in cowpea. Plant hormone pathways showing preferential expression at particular reproductive stages were identified. Expression of epigenetic pathways, resembling those found in Arabidopsis, including microRNA mediated gene silencing, RNA directed DNA methylation and histone modification were associated with particular stages of male and female gametophyte development, suggesting roles in gametogenic cell specification and elaboration. Analyses of cell-cycle related gene expression in mature cowpea female gametophytes, indicated that the egg and central cell were arrested at the G1/S and G2/M cell cycle phases, respectively, prior to fertilization. Pre-fertilization female gametophyte arrest was characterized by barely detectable auxin biosynthesis gene expression levels, and elevated expression of genes involved in RNA-mediated gene silencing and histone modification. These transcriptomes provide a useful resource for additional interrogation to support functional analyses for development of higher yielding cowpea and syntenic legume crops.
One sentence summary
Transcriptomes from cowpea reproductive cell-types isolated in temporal sequence from meiosis to seed initiation revealed cell-type gene expression profiles enabling comparison with gene expression pathways known to function in cell specification and reproductive development in other plants.
“…In addition, some genes that cause male sterility in rice may affect more than the male gametogenesis, as they may have other mutant related defects. For example, the mutant osemf2bā4 exhibited a reduced grain number and seed set and the phenotype was shorter than the wild type (Deng et al, ); the mutant osppr676 displayed retarded growth and partial sterility in the pollen grains (Liu et al, ) and this renders these genes unsuitable for hybrid breeding. In this study, we successfully replicated the maleāsterile phenotype of Oswbc11 mutant in rice using CRISPR/Cas9.…”
Commercial application of nuclear genetic male sterility has been improved recently by a novel technique, Seed Production Technology (SPT), which incorporates transgenic maintainer lines capable of propagating nonātransgenic nuclear maleāsterile lines for use as female parents in hybrid production. Here, we identified a rice nuclear maleāsterile mutant, Oswbc11, with abnormal pollen development and lipid transport. We finely mapped the Oswbc11 gene into a 12.5ākb region on chromosome 10 and found one candidate gene, which had a base substitution (C to T) resulting in a premature stop codon and was functionally confirmed by CRISPR/Cas9 technology. Gene OsWBC11 encodes a subāfamily member of adenosine triphosphateābinding cassette transporter, which participates in the active transport of a wide range of molecules across membranes. Moreover, the agronomic traits of Oswbc11 mutants showed no significant differences compared to the wildātype control except for the seed setting rate. These results indicated that Oswbc11 gene could be used in rice hybrid breeding as a recessive nuclear maleāsterile gene combined with CRISPR/Cas9 and the SPT technology and applied in different rice varieties.
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