zma-miR159 targets ZmMYB74 and ZmMYB138 transcription factors to regulate grain size and weight in maize.

Endosperm cell number is critical in determining grain size in maize (Zea mays). Here, zma-miR159 overexpression led to enlarged grains in independent transgenic lines, suggesting that zma-miR159 contributes positively to maize grain size. Targeting of ZmMYB74 and ZmMYB138 transcription factor genes by zma-miR159 was validated using 5' RACE and dual-luciferase assay. Lines in which ZmMYB74 was knocked out using clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) presented a similar enlarged grain phenotype as those with zma-miR159 overexpression. Downstream genes regulating cell division were identified through DNA affinity purification sequencing using ZmMYB74 and ZmMYB138. Our results suggest that zma-miR159-ZmMYB modules act as an endosperm development hub, participating in the division and proliferation of endosperm cells.

Dynamic patterns of gene expression and regulatory variation in the maize seed coat.

BACKGROUND: Seed size is an important factor contributing to maize yield, but its molecular mechanism remains unclear. The seed coat, which serves as one of the three components of the maize grain, determines seed size to a certain extent. The seed coat also shares the maternal genotype and is an ideal material for studying heterosis. RESULTS: In this study, the self-pollinated seeds of the maize hybrid Yudan888 and its parental lines were continuously collected from 0 day after pollination (DAP) to 15 DAP for phenotyping, cytological observation and RNA-seq. The phenotypic data showed that 3 DAP and 8 DAP are the best time points to study maize seed coat heterosis. Cytological observations indicated that maize seed coat heterosis might be the result of the coordination between cell number and cell size. Furthermore, the RNA-seq results showed that the nonadditive genes changed significantly between 3 and 8 DAP. However, the number of genes expressed additively was not significantly different. Our findings suggest that seed coat heterosis in hybrid is the result of nonadditive expression caused by dynamic changes in genes at different time points during seed expansion and seed coat development. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment indicated that genes related to DNA replication, cell cycle regulation, circadian rhythms and metabolite accumulation contributed significantly to hybrid seed coat heterosis. CONCLUSION: Maize seed coat phenotyping allowed us to infer that 3 DAP and 8 DAP are important time points in the study of seed coat heterosis. Our findings provide evidence for genes involved in DNA replication, cell cycle regulation, circadian rhythms and metabolite accumulation in hybrid with high or low parental expression as major contributors to hybrid seed coat heterosis.

Comparative transcriptomics analysis at the key stage of maize ear development dissect heterosis.

Important traits related to maize (Zea mays L.) grain yield, such as kernel row number, ear length, kernel number per row, are determined during the development of female inflorescence. There is a significant positive correlation between yield component and the activity of inflorescence meristem (IM). To find the key stage of heterosis in the development of the ear, immature ears (from the IM stage until the end of the floral meristem [FM] stage) of Yudan888 and its parent lines were sampled to assay phenotype and for comparative transcriptomics analysis. The immature ear length of Yudan888 at the IM stage fitted an additive (mid-parental) model, but it showed high parental dominance at the spikelet-pair meristem (SPM) stage. Comparative analysis of transcriptomes suggested significant differences between additive and nonadditive expression patterns for different developmental stages. The number of distinct maternal or paternal genes (DMP) (genes expressed only in one parental line and their hybrid but silenced in another line) was greater than ABF1 (genes expressed in both parental lines but silenced in hybrid) at each stage. Gene Ontology (GO) enrichment suggested that the cell redox homeostasis genes with overdominance expression patterns in hybrids have an important contribution to heterosis. According to our research, an ear length heterosis network was established. The discovery of the inflection point for ear length heterosis allows us for inferring that the transition state of IM to SPM may be the starting point of ear length heterosis. These findings improved the understanding of maize ear length heterosis.

Suppression of microRNA168 enhances salt tolerance in rice (Oryza sativa L.).

BACKGROUND: Rice is a salt-sensitive crop. Complex gene regulatory cascades are likely involved in salinity stress in rice roots. microRNA168 (miR168) is a conserved miRNA among different plant species. It in-directly regulates the expression of all miRNAs by targeting gene ARGONAUTE1(AGO1). Short Tandem Target Mimic (STTM) technology is an ideal approach to study miRNA functions by in-activating mature miRNA in plants. RESULTS: In this study, rice miR168 was inactivated by STTM. The T3 generation seedlings of STTM168 exhibited significantly enhanced salt resistance. Direct target genes of rice miR168 were obtained by in silico prediction and further confirmed by degradome-sequencing. PINHEAD (OsAGO1), which was previously suggested to be a plant abiotic stress response regulator. RNA-Seq was performed in root samples of 150mM salt-treated STTM168 and control seedlings. Among these screened 481 differentially expressed genes within STTM168 and the control, 44 abiotic stress response related genes showed significant difference, including four known salt-responsive genes. CONCLUSION: Based on sequencing and qRT-PCR, a "miR168-AGO1-downstream" gene regulation model was proposed to be responsible for rice salt stress response. The present study proved miR168-AGO1 cascade to play important role in rice salinity stress responding, as well as to be applied in agronomic improvement in further.

Gene expression variation explains maize seed germination heterosis.

BACKGROUND: Heterosis has been extensively utilized in plant breeding, however, the underlying molecular mechanism remains largely elusive. Maize (Zea mays), which exhibits strong heterosis, is an ideal material for studying heterosis. RESULTS: In this study, there is faster imbibition and development in reciprocal crossing Zhengdan958 hybrids than in their parent lines during seed germination. To investigate the mechanism of heterosis of maize germination, comparative transcriptomic analyses were conducted. The gene expression patterns showed that 1324 (47.27%) and 1592 (66.44%) of the differential expression genes between hybrids and either parental line display parental dominance up or higher levels in the reciprocal cross of Zhengdan958, respectively. Notably, these genes were mainly enriched in metabolic pathways, including carbon metabolism, glycolysis/gluconeogenesis, protein processing in endoplasmic reticulum, etc. CONCLUSION: Our results provide evidence for the higher expression level genes in hybrid involved in metabolic pathways acting as main contributors to maize seed germinating heterosis. These findings provide new insights into the gene expression variation of maize embryos and improve the understanding of maize seed germination heterosis.

Fine-tuning shoot meristem size to feed the world.

In order to maintain food security for the world's growing population, crop yields need to be significantly improved. Domestication and crop improvement involve modification of traits such as fruit size and seed number to optimize productivity. Although these traits are selected at the mature stage, they are determined during the development of shoot meristem, a tissue that forms successive meristems and reproductive organs that make edible fruits or seeds. Therefore, the architecture of reproductive organs and yield-related traits are determined during the maturation of shoot meristem. Here, we highlight recent progress in understanding how shoot meristem size affects yield-related traits and outline the strategies to fine-tune meristem regulatory genes to meet the demands of a growing population and promote sustainable agriculture.

Mechanism of phosphate adsorption on superparamagnetic microparticles modified with transitional elements: Experimental observation and computational modelling.

Microparticle sorbents (MPSs) containing nano-Fe3O4 core, nano-layered double hydroxides shell modified with different transitional elements (TE-MPSs) are effective for capturing phosphate from wastewater. In present article, different TE-MPSs loaded with Ce, La, Zr and Hf were synthesized and the phosphorous removal performances were compared. The molecular-level mechanism of phosphate adsorption was successfully simulated by pseudo-atom model based on virtual crystal approximation method, which was in line with the spectroscopic data. The results confirmed the inter-sphere complexation reaction between phosphate and TE-MPSs under neutral pH. And the adsorption mechanism probably changed during cycles of adsorption/regeneration. As revealed by elemental composition analysis, ion exchange mechanism probably played an important part in phosphate adsorption in Cycle 1 while the ligand complexation became dominant after regenerated with NaOH in the following cycles. This work indicates that the highly effective, easily separable and repeatedly usable TE-MPSs has the potential for phosphate sequestration and recovery from sewage wastewater.

Identification of Quantitative Trait Loci and Candidate Genes for Maize Starch Granule Size through Association Mapping.

Starch is an important nutrient component of maize kernels, and starch granule size largely determines kernel waxiness, viscosity, and other physiochemical and processing properties. To explore the genetic basis of maize starch granule size, 266 tropical, subtropical, and temperate inbred lines were subjected to genome-wide association analyses with an array of 56,110 random single nucleotide polymorphisms (SNPs). In the present panel, the kernel starch granule size ranged from 7-15.8 µm long and 6.8-14.3 µm wide. Fourteen significant SNPs were identified as being associated with the length of starch granules and 9 with their width. One linkage disequilibrium block flanking both sides of a significant SNP was defined as a quantitative trait locus (QTL) interval, and seven QTLs were mapped for both granule length and width. A total of 79 and 88 candidate genes associated with starch length and width, respectively, were identified as being distributed on QTL genomic regions. Among these candidate genes, six with high scores were predicted to be associated with maize starch granule size. A candidate gene association analysis identified significant SNPs within genes GRMZM2G419655 and GRMZM2G511067, which could be used as functional markers in screening starch granule size for different commercial uses.