A Gene Expression Profiling of Early Rice Stamen Development that Reveals Inhibition of Photosynthetic Genes by OsMADS58

OsMADS58 Stabilizes Gene Regulatory Circuits during Rice Stamen Development

Rice (Oryza sativa) OsMADS58 is a C-class MADS box protein, and characterization of a transposon insertion mutant osmads58 suggested that OsMADS58 plays a role in stamen development. However, as no null mutation has been obtained, its role has remained unclear. Here, we report that the CRISPR knockout mutant osmads58 exhibits complex altered phenotypes, including anomalous diploid germ cells, aberrant meiosis, and delayed tapetum degeneration. This CRISPR mutant line exhibited stronger changes in expression of OsMADS58 target genes compared with the osmads58 dSpm (transposon insertion) line, along with changes in multiple pathways related to early stamen development. Notably, transcriptional regulatory circuits in young panicles covering the stamen at stages 4-6 were substantially altered in the CRISPR line compared to the dSpm line. These findings strongly suggest that the pleiotropic effects of OsMADS58 on stamen development derive from a potential role in stabilizing gene regulatory circuits during early stamen development. Thus, this work opens new avenues for viewing and deciphering the regulatory mechanisms of early stamen development from a network perspective.

Population Structure of Nation-Wide Rice in Thailand

BACKGROUND

Thailand is a country with large diversity in rice varieties due to its rich and diverse ecology. In this paper, 300 rice accessions from all across Thailand were sequenced to identify SNP variants allowing for the population structure to be explored.

RESULTS

The result of inferred population structure from admixture and clustering analysis illustrated strong evidence of substructure in each geographical region. The results of phylogenetic tree, PCA analysis, and machine learning on population identifying SNPs also supported the inferred population structure.

CONCLUSION

The population structure inferred in this study contains five subpopulations that tend to group individuals based on location. So, each subpopulation has unique genetic patterns, agronomic traits, as well as different environmental conditions. This study can serve as a reference point of the nation-wide population structure for supporting breeders and researchers who are interested in Thai rice.

Auxin guides germ-cell specification in Arabidopsis anthers

Germ cells (GCs) are the key carriers delivering genetic information from one generation to the next. In a majority of animals, GCs segregate from somatic cells during embryogenesis by forming germlines. In land plants, GCs segregate from somatic cells during postembryonic development. In a majority of angiosperms, male GCs (archesporial cells) initiate at the four corners of the anther primordia. Little is known about the mechanism underlying this initiation. Here, we discovered that the dynamic auxin distribution in developing anthers coincided with GC initiation. A centripetal auxin gradient gradually formed toward the four corners where GCs will initiate. Local auxin biosynthesis was necessary for this patterning and for GC specification. The GC determinant protein SPOROCYTELESS/NOZZLE (SPL/NZZ) mediated the effect of auxin on GC specification and modified auxin biosynthesis to maintain a centripetal auxin distribution. Our work reveals that auxin is a key factor guiding GC specification in Arabidopsis anthers. Moreover, we demonstrate that the GC segregation from somatic cells is not a simple switch on/off event but rather a complicated process that involves a dynamic feedback circuit among local auxin biosynthesis, transcription of SPL/NZZ, and a progressive GC specification. This finding sheds light on the mystery of how zygote-derived somatic cells diverge into GCs in plants.

A basic/helix-loop-helix transcription factor controls leaf shape by regulating auxin signaling in apple

Climate-driven phenological change across local spatial gradients leads to leaf shape variation. At higher elevations, leaves of broadleaf species tend to become narrower, but the underlying molecular mechanism is largely unknown. In this study, a series of morphometric analyses and biochemical assays, combined with functional identification in apple, were performed. We show that the decrease in apple leaf width with increasing altitude is controlled by a basic/helix-loop-helix transcription factor (bHLH TF), MdbHLH3. The MdbHLH3-overexpressing lines have a lower transcript abundance of MdPIN1 encoding an auxin efflux carrier but a higher transcript abundance of MdGH3-2 encoding a putative auxin amido conjugate synthase, resulting in a lower free auxin concentration; feeding the transgenic leaves with exogenous auxin partially restores leaf width. MdbHLH3 transcriptionally suppresses and activates MdPIN1 and MdGH3-2, respectively, by specifically binding to their promoters. This alters auxin homeostasis and transport, consequently leading to changes in leaf shape. These findings suggest that the bHLH TF MdbHLH3 directly modulates auxin signaling in controlling leaf shape in response to local spatial gradients in apple.

Spatiotemporal Resolved Leaf Angle Establishment Improves Rice Grain Yield via Controlling Population Density

Leaf angle is mainly determined by the lamina joint (LJ) and contributes to ideal crop architecture for high yield. Here, we dissected five successive stages with distinct cytological features of LJs spanning organogenesis to leaf angle formation and obtained the underlying stage-specific mRNAs and small RNAs, which well explained the cytological dynamics during LJ organogenesis and leaf angle plasticity. Combining the gene coexpression correlation with high-throughput promoter analysis, we identified a set of transcription factors (TFs) determining the stage- and/or cytological structure-specific profiles. The functional studies of these TFs demonstrated that cytological dynamics determined leaf angle and that the knockout rice of these TFs with erect leaves significantly enhanced yield by maintaining the proper tiller number under dense planting. This work revealed the high-resolution mechanisms of how the cytological dynamics of LJ determined leaf erectness and served as a valuable resource to remodel rice architecture for high yield by controlling population density.

Jasmonate Signaling Enhances RNA Silencing and Antiviral Defense in Rice

Small RNA-mediated RNA silencing is an important antiviral mechanism in higher plants. It has been shown that RNA silencing components can be upregulated by viral infection. However, the mechanisms underlying the upregulation remain largely unknown. Here, we show that jasmonate (JA) signaling transcriptionally activates Argonaute 18 (AGO18), a core RNA silencing component that promotes rice antiviral defense through sequestering miR168 and miR528, which repress key antiviral defense proteins. Mechanistically, the JA-responsive transcription factor JAMYB directly binds to the AGO18 promoter to activate AGO18 transcription. Rice stripe virus (RSV) coat protein (CP) triggers JA accumulation and upregulates JAMYB to initiate this host defense network. Our study reveals that regulatory crosstalk exists between the JA signaling and antiviral RNA silencing pathways and elucidates a molecular mechanism for CP-mediated viral resistance in monocot crops.

A Bridge to the World

Zhi-Hong Xu is a plant physiologist who studied botany at Peking University (1959–1965). He joined the Shanghai Institute of Plant Physiology (SIPP), Chinese Academy of Sciences (CAS), as a graduate student in 1965. He recalls what has happened for the institute, during the Cultural Revolution, and he witnessed the spring of science eventually coming to China. Xu was a visiting scholar at the John Innes Institute and in the Department of Botany at Nottingham University in the United Kingdom (1979–1981). He became deputy director of SIPP in 1983 and director in 1991; he also chaired the State Key Laboratory of Plant Molecular Genetics SIPP (1988–1996). He worked as a visiting scientist in the Institute of Molecular and Cell Biology, National University of Singapore, for three months each year (1989–1992). He served as vice president of CAS (1992–2002) and as president of Peking University (1999–2008). Over these periods he was heavily involved in the design and implementation of major scientific projects in life sciences and agriculture in China. He is an academician of CAS and member of the Academy of Sciences for the Developing World. His scientific contributions mainly cover plant tissue culture, hormone mechanism in development, as well as plant developmental response to environment. Xu, as a scientist and leader who has made an impact in the community, called up a lot of excellent young scientists returning to China. His efforts have promoted the fast development of China's plant and agricultural sciences.

Genome-wide analysis of spatiotemporal gene expression patterns during floral organ development in Brassica rapa

Flowering is a key agronomic trait that directly influences crop yield and quality and serves as a model system for elucidating the molecular basis that controls successful reproduction, adaptation, and diversification of flowering plants. Adequate knowledge of continuous series of expression data from the floral transition to maturation is lacking in Brassica rapa. To unravel the genome expression associated with the development of early small floral buds (< 2 mm; FB2), early large floral buds (2-4 mm; FB4), stamens (STs) and carpels (CPs), transcriptome profiling was carried out with a Br300K oligo microarray. The results showed that at least 6848 known nonredundant genes (30% of the genes of the Br300K) were differentially expressed during the floral transition from vegetative tissues to maturation. Functional annotation of the differentially expressed genes (DEGs) (fold change ≥ 5) by comparison with a close relative, Arabidopsis thaliana, revealed 6552 unigenes (4579 upregulated; 1973 downregulated), including 131 Brassica-specific and 116 functionally known floral Arabidopsis homologs. Additionally, 1723, 236 and 232 DEGs were preferentially expressed in the tissues of STs, FB2, and CPs. These DEGs also included 43 transcription factors, mainly AP2/ERF-ERF, NAC, MADS-MIKC, C2H2, bHLH, and WRKY members. The differential gene expression during flower development induced dramatic changes in activities related to metabolic processes (23.7%), cellular (22.7%) processes, responses to the stimuli (7.5%) and reproduction (1%). A relatively large number of DEGs were observed in STs and were overrepresented by photosynthesis-related activities. Subsequent analysis via semiquantitative RT-PCR, histological analysis performed with in situ hybridization of BrLTP1 and transgenic reporter lines (BrLTP promoter::GUS) of B. rapa ssp. pekinensis supported the spatiotemporal expression patterns. Together, these results suggest that a temporally and spatially regulated process of the selective expression of distinct fractions of the same genome leads to the development of floral organs. Interestingly, most of the differentially expressed floral transcripts were located on chromosomes 3 and 9. This study generated a genome expression atlas of the early floral transition to maturation that represented the flowering regulatory elements of Brassica rapa.

Genome-wide transcriptome profiling provides insights into panicle development of rice (Oryza sativa L.)

Panicle architecture is an important component of agronomic trait in rice, which is also a key ingredient that could influence yield and quality of rice. In the panicle growth and development process, there are a series of complicated molecular and cellular events which are regulated by many interlinking genes. In this study, to explore the potential mechanism and identify genes and pathways involved in the formation of rice panicle, we compared the transcriptional profile of rice panicles (NIL-GW8 and NIL-gw8^Amol) at three different stages of panicle development: In5 (formation of higher-order branches), In6 (differentiation of glumes) and In7 (differentiation of floral organs). A range of 40.5 to 54.1 million clean reads was aligned to 31,209 genes in our RNA-Seq analysis. In addition, we investigated transcriptomic changes between the two rice lines during different stages. A total of 726, 1121 and 2584 differentially expressed genes (DEGs) were identified at stages 1, 2 and 3, respectively. Based on an impact analysis of the DEGs, we hypothesize that MADS-box gene family, cytochrome P450 (CYP) and pentatricopeptide repeat (PPR) protein and various transcription factors may be involved in regulation of panicle development. Further, we also explored the functional properties of DEGs by gene ontology analysis, and the results showed that different numbers of DEGs genes were associated with 53 GO groups. In KEGG pathway enrichment analysis, many DEGs related to biosynthesis of secondary metabolites and plant hormone signal transduction, suggesting their important roles during panicle development. This study provides the first examination of changes in gene expression between different panicle development stages in rice. Our results of transcriptomic characterization provide important information to elucidate the complex molecular and cellular events about the panicle formation in rice or other cereal crops. Also, the findings will be helpful for the further identification of the genes related to panicle development.

Characterization of the Ubiquitin C-Terminal Hydrolase and Ubiquitin-Specific Protease Families in Rice (Oryza sativa)

The ubiquitin C-terminal hydrolase (UCH) and ubiquitin-specific processing protease (UBP) protein families both function in protein deubiquitination, playing important roles in a wide range of biological processes in animals, fungi, and plants. Little is known about the functions of these proteins in rice (Oryza sativa), and the numbers of genes reported for these families have not been consistent between different rice database resources. To further explore their functions, it is necessary to first clarify the basic molecular and biochemical nature of these two gene families. Using a database similarity search, we clarified the numbers of genes in these two families in the rice genome, examined the enzyme activities of their corresponding proteins, and characterized the expression patterns of all OsUCH and representative OsUBP genes. Five OsUCH and 44 OsUBP genes were identified in the rice genome, with four OsUCH proteins and 10 of 16 tested representative OsUBP proteins showing enzymatic activities. Two OsUCHs and five OsUBPs were found to be preferentially expressed in the early development of rice stamens. This work thus lays down a reliable bioinformatic foundation for future investigations of genes in these two families, particularly for exploring their potential roles in rice stamen development.

Reconsideration of Plant Morphological Traits: From a Structure-Based Perspective to a Function-Based Evolutionary Perspective

This opinion article proposes a novel alignment of traits in plant morphogenesis from a function-based evolutionary perspective. As a member species of the ecosystem on Earth, we human beings view our neighbor organisms from our own sensing system. We tend to distinguish forms and structures (i.e., "morphological traits") mainly through vision. Traditionally, a plant was considered to be consisted of three parts, i.e., the shoot, the leaves, and the root. Based on such a "structure-based perspective," evolutionary analyses or comparisons across species were made on particular parts or their derived structures. So far no conceptual framework has been established to incorporate the morphological traits of all three land plant phyta, i.e., bryophyta, pteridophyta and spermatophyta, for evolutionary developmental analysis. Using the tenets of the recently proposed concept of sexual reproduction cycle, the major morphological traits of land plants can be aligned into five categories from a function-based evolutionary perspective. From this perspective, and the resulting alignment, a new conceptual framework emerges, called "Plant Morphogenesis 123." This framework views a plant as a colony of integrated plant developmental units that are each produced via one life cycle. This view provided an alternative perspective for evolutionary developmental investigation in plants.

Phylogenetic tree-informed microRNAome analysis uncovers conserved and lineage-specific miRNAs in Camellia during floral organ development

In plants, miRNAs are endogenous small RNAs derived from single-stranded precursors with hairpin structures. The evolution of miRNAs and their targets represents one of the most dynamic circuits directing gene expression, which may play fundamental roles in shaping the development of distinct plant organs. Here we performed high-throughput small RNA sequencing in five organ types of Camellia azalea to capture the spatial profile of small non-coding RNA. In total we obtained >227 million high-quality reads and identified 175 miRNAs with mature and precursor sequences. We aligned the miRNAs to known miRNA databases and revealed some conserved as well as 'newly evolved' miRNA genes. Twelve miRNAs were identified to be specific in the genus Camellia, supporting the lineage-specific manner of expansion of 'young' miRNAs. Through differential expression analysis, we showed that many miRNAs were preferentially abundant in certain organ types. Moreover, hierarchical clustering analysis revealed distinctive expression patterns of tissue-specific miRNAs. Gene Ontology enrichment analysis of targets of stamen- and carpel-specific miRNA subclusters showed that miRNA-target regulatory circuits were involved in many important biological processes, enabling their proper specification and organogenesis, such as 'DNA integration' and 'fruit development'. Further, quantitative PCR of key miRNAs and their target genes revealed anti-correlated patterns, and uncovered the functions of key miRNA-target pairs in different floral organs. Taken together, this work yielded valuable information on miRNA-target regulation in the control of floral organ development and sheds light on the evolution of lineage-specific miRNAs in Camellia.