RNA-Binding Protein MAC5A Is Required for Gibberellin-Regulated Stamen Development.

The development of floral organs is coordinated by an elaborate network of homeotic genes, and gibberellin (GA) signaling is involved in floral organ development; however, the underlying molecular mechanisms remain elusive. In the present study, we found that MOS4-ASSOCIATED COMPLEX 5A (MAC5A), which is a protein containing an RNA-binding motif, was involved in the development of sepals, petals, and stamens; either the loss or gain of MAC5A function resulted in stamen malformation and a reduced seed set. The exogenous application of GA considerably exacerbated the defects in mac5a null mutants, including fewer stamens and male sterility. MAC5A was predominantly expressed in pollen grains and stamens, and overexpression of MAC5A affected the expression of homeotic genes such as APETALA1 (AP1), AP2, and AGAMOUS (AG). MAC5A may interact with RABBIT EARS (RBE), a repressor of AG expression in Arabidopsis flowers. The petal defect in rbe null mutants was at least partly rescued in mac5a rbe double mutants. These findings suggest that MAC5A is a novel factor that is required for the normal development of stamens and depends on the GA signaling pathway.

TGIF-DB: terse genomics interface for developing botany.

OBJECTIVES: Pearl millet (Pennisetum glaucum) is a staple cereal crop for semi-arid regions. Its whole genome sequence and deduced putative gene sequences are available. However, the functions of many pearl millet genes are unknown. Situations are similar for other crop species such as garden asparagus (Asparagus officinalis), chickpea (Cicer arietinum) and Tartary buckwheat (Fagopyrum tataricum). The objective of the data presented here was to improve functional annotations of genes of pearl millet, garden asparagus, chickpea and Tartary buckwheat with gene annotations of model plants, to systematically provide such annotations as well as their sequences on a website, and thereby to promote genomics for those crops. DATA DESCRIPTION: Sequences of genomes and transcripts of pearl millet, garden asparagus, chickpea and Tartary buckwheat were downloaded from a public database. These transcripts were associated with functional annotations of their Arabidopsis thaliana and rice (Oryza sativa) counterparts identified by BLASTX. Conserved domains in protein sequences of those species were identified by the HMMER scan with the Pfam database. The resulting data was deposited in the figshare repository and can be browsed on the Terse Genomics Interface for Developing Botany (TGIF-DB) website ( http://webpark2116.sakura.ne.jp/rlgpr/ ).

A GDSL-type esterase/lipase gene, GELP77, is necessary for pollen dissociation and fertility in Arabidopsis.

Pollen wall characteristics are dramatically changed during pollen maturation. Many genes have been identified as regulators of such changes in pollen wall characteristics, but mechanisms of such changes have not been completely understood. Here, a GDSL-type esterase/lipase gene, GELP77, is shown to regulate such changes in Arabidopsis thaliana. GELP77-deficient (gelp77) plants exhibited male sterility, and this phenotype was suppressed by introduction of a GELP77 genomic fragment. Mature pollen grains of wild-type Arabidopsis plants have an organized reticulate surface structure and are dissociated from each other. In contrast, pollen grains of gelp77 lacked such a structure and were shrunken and stuck to each other. Nuclei were not detectable in gelp77 microspores at a putative uninucleate stage, suggesting that GELP77 is required as early as this stage. In plants that have the GELP77 promoter-GELP77-GFP transgene, the GELP77-GFP fusion protein was detected in microspores, tapetal cells and middle layer cells in anthers at post-meiotic stages, whereas not anthers at pre-meiotic stages. Analysis of amino acid sequences suggests that GELP77 is phylogenetically distant from the other 104 GDSL-type esterase/lipase genes in Arabidopsis and that GELP77 orthologs are present in various plant species. Together, these results indicate that GELP77 regulates pollen wall characteristics in Arabidopsis.

A putative AGAMOUS ortholog is a candidate for the gene determining ease of dehulling in Tartary buckwheat (Fagopyrum tataricum).

MAIN CONCLUSION: Tartary buckwheat rice-type cultivars, which allow easy dehulling, lacked periclinal cell divisions that proceed underneath the epidermis in the proximity of ovary midribs in non-rice-type cultivars. The easy dehulling in these cultivars was associated with a G→A substitution in an AGAMOUS ortholog. Ease of dehulling in Tartary buckwheat (Fagopyrum tataricum) can affect the quality of its products. Tartary buckwheat cultivars that allow easy dehulling are called rice-type cultivars. The rice and non-rice hull types are determined by a single gene, but this gene is unclear. Here, we show that cells underneath the epidermis in the proximity of ovary midribs undergo periclinal cell divisions in non-rice-type cultivars but do not in a rice-type cultivar. The cells that arose from the periclinal cell divisions later underwent lignification, which should increase mechanical strength of hulls. In RNA sequencing, a partial mRNA of an AGAMOUS ortholog in Tartary buckwheat (FtAG) was found to be absent in the rice-type cultivar. Cloning of this gene revealed that this is a 42-bp deletion due to a G→A substitution at a splice acceptor site in the FtAG genomic region. In F2 progeny derived from a cross between non-rice-type and rice-type cultivars, all the rice-type plants exhibited the homozygous A/A allele at this site, whereas all the Tartary-type plants exhibited either the homozygous G/G allele or the heterozygous A/G allele. These results suggest that FtAG is a candidate for the gene that determines ease of dehulling in Tartary buckwheat. The DNA marker that we developed to distinguish the FtAG alleles can be useful in breeding Tartary buckwheat cultivars.

B-family subunits of protein phosphatase 2A are necessary for pollen development but not for female gametophyte development in Arabidopsis.

Protein phosphatase 2A (PP2A) is a heterotrimeric protein complex conserved among eukaryotes. The B subunit of PP2A determines the substrate specificity of the PP2A holoenzyme, and is classified into the B, B', B″ and B‴ families. Arabidopsis thaliana has two isoforms of the B-family subunit (ATBA and ATBB). A double knockout of their genes is lethal, but which developmental process is primarily impaired by the double knockout is unclear. Identifying such a process helps understand PP2A-mediated signaling more deeply. Here, genetic characterization of new knockout mutants for these genes shows that they are necessary for pollen development but not for female gametophyte development. Compared to wild-type pollen grains, the mutant pollen grains exhibited lower enzyme activities, germinated less frequently on stigmas, and exhibited the aberrant numbers of sperm cell nuclei, suggesting that ATBA and ATBB play pleiotropic roles in pollen development. The amino acids stabilizing the interaction between the human PP2A A and B-family subunits are conserved in an Arabidopsis A subunit (AtPP2AA2), ATBA and ATBB. His-tagged AtPP2AA2 co-immunoprecipitated with either Myc-tagged ATBA or Myc-tagged ATBB in vitro, confirming their interactions. Proteins that regulate pollen development and that undergo dephosphorylation are likely primary targets of ATBA and ATBB.

Stage- and tissue-specific expression of rice OsIsu1 gene encoding a scaffold protein for mitochondrial iron-sulfur-cluster biogenesis.

Isu is a scaffold protein involved in mitochondrial iron-sulfur-cluster biogenesis, which affects redox and iron homeostasis in human and yeast cells. A BLASTP search identified two putative Isu genes in rice, and we designated one of them as OsIsu1. When expressed in onion epidermal cells, OsIsu1::GFP was localized to the mitochondria. Northern analysis showed that OsIsu1 was down-regulated in iron-deficient rice root. OsIsu1 promoter-GUS was introduced into Arabidopsis thaliana and histochemical GUS-staining showed that OsIsu1 expression was regulated in a stage- and tissue-specific manner. OsIsu1 was expressed ectopically in Arabidopsis under the control of the CaMV35S promoter, which increased weight of plants.