Live and let die - the B(sister) MADS-box gene OsMADS29 controls the degeneration of cells in maternal tissues during seed development of rice (Oryza sativa)

Genome-Wide Analyses of MADS-Box Genes Reveal Their Involvement in Seed Development and Oil Accumulation of Tea-Oil Tree (Camellia oleifera)

The seeds of Camellia oleifera produce high amount of oil, which can be broadly used in the fields of food, industry, and medicine. However, the molecular regulation mechanisms of seed development and oil accumulation in C. oleifera are unclear. In this study, evolutionary and expression analyses of the MADS-box gene family were performed across the C. oleifera genome for the first time. A total of 86 MADS-box genes (ColMADS) were identified, including 60 M-type and 26 MIKC members. More gene duplication events occurred in M-type subfamily (6) than that in MIKC subfamily (2), and SEP-like genes were lost from the MIKCC clade. Furthermore, 8, 15, and 17 differentially expressed ColMADS genes (DEGs) were detected between three developmental stages of seed (S1/S2, S2/S3, and S1/S3), respectively. Among these DEGs, the STK-like ColMADS12 and TT16-like ColMADS17 were highly expressed during the seed formation (S1 and S2), agreeing with their predicted functions to positively regulate the seed organogenesis and oil accumulation. While ColMADS57 and ColMADS07 showed increasing expression level with the seed maturation (S2 and S3), conforming to their potential roles in promoting the seed ripening. In all, these results revealed a critical role of MADS-box genes in the C. oleifera seed development and oil accumulation, which will contribute to the future molecular breeding of C. oleifera.

Transcription factor OsSHR2 regulates rice architecture and yield per plant in response to nitrogen

MAIN CONCLUSION

Mutation of OsSHR2 adversely impacted root and shoot growth and impaired plant response to N conditions, further reducing the yield per plant. Nitrogen (N) is a crucial factor that regulates the plant architecture. There is still a lack of research on it. In our study, it was observed that the knockout of the SHORTROOT 2 (OsSHR2) which was induced by N deficiency, can significantly affect the regulation of plant architecture response to N in rice. Under N deficiency, the mutation of OsSHR2 significantly reduced root growth, and impaired the sensitivity of the root meristem length to N deficiency. The mutants were found to have approximately a 15% reduction in plant height compared to wild type. But mutants showed a significant increase in tillering at post-heading stage, approximately 26% more than the wild type, particularly in high N conditions. In addition, due to reduced seed setting rate and 1000-grain weight, mutant yield was significantly decreased by approximately 33% under low N fertilizer supply. The mutation also changed the distribution of N between the vegetative and reproductive organs. Our findings suggest that the transcription factor OsSHR2 plays a regulatory role in the response of plant architecture and yield per plant to N in rice.

A novel OsHB5-OsAPL-OsMADS27/OsWRKY102 regulatory module regulates grain size in rice

Grain size, a crucial trait that determines rice yield and quality, is typically regulated by multiple genes. Although numerous genes controlling grain size have been identified, the precise and dynamic regulatory network governing grain size is still not fully understood. In this study, we unveiled a novel regulatory module composed of OsHB5, OsAPL and OsMADS27/OsWRKY102, which plays a crucial role in modulating grain size in rice. As a positive regulator of grain size, OsAPL has been found to interact with OsHB5 both in vitro and in vivo. Through chromatin immunoprecipitation-sequencing, we successfully mapped two potential targets of OsAPL, namely OsMADS27, a positive regulator in grain size and OsWRKY102, a negative regulator in lignification that is also associated with grain size control. Further evidence from EMSA and chromatin immunoprecipitation-quantitative PCR experiments has shown that OsAPL acts as an upstream transcription factor that directly binds to the promoters of OsMADS27 and OsWRKY102. Moreover, EMSA and dual-luciferase reporter assays have indicated that the interaction between OsAPL and OsHB5 enhances the repressive effect of OsAPL on OsMADS27 and OsWRKY102. Collectively, our findings discovered a novel regulatory module, OsHB5-OsAPL-OsMADS27/OsWRKY102, which plays a significant role in controlling grain size in rice. These discoveries provide potential targets for breeding high-yield and high-quality rice varieties.

The Soybean Expression Atlas v2: A comprehensive database of over 5000 RNA-seq samples

Soybean is a crucial crop worldwide, used as a source of food, feed, and industrial products due to its high protein and oil content. Previously, the rapid accumulation of soybean RNA-seq data in public databases and the computational challenges of processing raw RNA-seq data motivated us to develop the Soybean Expression Atlas, a gene expression database of over a thousand RNA-seq samples. Over the past few years, our database has allowed researchers to explore the expression profiles of important gene families, discover genes associated with agronomic traits, and understand the transcriptional dynamics of cellular processes. Here, we present the Soybean Expression Atlas v2, an updated version of our database with a fourfold increase in the number of samples, featuring transcript- and gene-level transcript abundance matrices for 5481 publicly available RNA-seq samples. New features in our database include the availability of transcript-level abundance estimates and equivalence classes to explore differential transcript usage, abundance estimates in bias-corrected counts to increase the accuracy of differential gene expression analyses, a new web interface with improved data visualization and user experience, and a reproducible and scalable pipeline available as an R package. The Soybean Expression Atlas v2 is available at https://soyatlas.venanciogroup.uenf.br/, and it will accelerate soybean research, empowering researchers with high-quality and easily accessible gene expression data.

Genome-Wide Identification of MADS-Box Genes in Taraxacum kok-saghyz and Taraxacum mongolicum: Evolutionary Mechanisms, Conserved Functions and New Functions Related to Natural Rubber Yield Formation

MADS-box transcription regulators play important roles in plant growth and development. However, very few MADS-box genes have been isolated in the genus Taraxacum, which consists of more than 3000 species. To explore their functions in the promising natural rubber (NR)-producing plant Taraxacum kok-saghyz (TKS), MADS-box genes were identified in the genome of TKS and the related species Taraxacum mongolicum (TM; non-NR-producing) via genome-wide screening. In total, 66 TkMADSs and 59 TmMADSs were identified in the TKS and TM genomes, respectively. From diploid TKS to triploid TM, the total number of MADS-box genes did not increase, but expansion occurred in specific subfamilies. Between the two genomes, a total of 11 duplications, which promoted the expansion of MADS-box genes, were identified in the two species. TkMADS and TmMADS were highly conserved, and showed good collinearity. Furthermore, most TkMADS genes exhibiting tissue-specific expression patterns, especially genes associated with the ABCDE model, were preferentially expressed in the flowers, suggesting their conserved and dominant functions in flower development in TKS. Moreover, by comparing the transcriptomes of different TKS lines, we identified 25 TkMADSs related to biomass formation and 4 TkMADSs related to NR content, which represented new targets for improving the NR yield of TKS.

Identification and validation of new MADS-box homologous genes in 3010 rice pan-genome

KEY MESSAGE

Identification and validation of ten new MADS-box homologous genes in 3010 rice pan-genome for rice breeding. The functional genome is significant for rice breeding. MADS-box genes encode transcription factors that are indispensable for rice growth and development. The reported 15,362 novel genes in the rice pan-genome (RPAN) of Asian cultivated rice accessions provided a useful gene reservoir for the identification of more MADS-box candidates to overcome the limitation for the usage of only 75 MADS-box genes identified in Nipponbare for rice breeding. Here, we report the identification and validation of ten MADS-box homologous genes in RPAN. Origin and identity analysis indicated that they are originated from different wild rice accessions and structure of motif analysis revealed high variations in their amino acid sequences. Phylogenetic results with 277 MADS-box genes in 41 species showed that all these ten MADS-box homologous genes belong to type I (SRF-like, M-type). Gene expression analysis confirmed the existence of these ten MADS-box genes in IRIS_313-10,394, all of them were expressed in flower tissues, and six of them were highly expressed during seed development. Altogether, we identified and validated experimentally, for the first time, ten novel MADS-box genes in RPAN, which provides new genetic sources for rice improvement.

Cytological, transcriptome and miRNome temporal landscapes decode enhancement of rice grain size

BACKGROUND

Rice grain size (GS) is an essential agronomic trait. Though several genes and miRNA modules influencing GS are known and seed development transcriptomes analyzed, a comprehensive compendium connecting all possible players is lacking. This study utilizes two contrasting GS indica rice genotypes (small-grained SN and large-grained LGR). Rice seed development involves five stages (S1-S5). Comparative transcriptome and miRNome atlases, substantiated with morphological and cytological studies, from S1-S5 stages and flag leaf have been analyzed to identify GS proponents.

RESULTS

Histology shows prolonged endosperm development and cell enlargement in LGR. Stand-alone and comparative RNAseq analyses manifest S3 (5-10 days after pollination) stage as crucial for GS enhancement, coherently with cell cycle, endoreduplication, and programmed cell death participating genes. Seed storage protein and carbohydrate accumulation, cytologically and by RNAseq, is shown to be delayed in LGR. Fourteen transcription factor families influence GS. Pathway genes for four phytohormones display opposite patterns of higher expression. A total of 186 genes generated from the transcriptome analyses are located within GS trait-related QTLs deciphered by a cross between SN and LGR. Fourteen miRNA families express specifically in SN or LGR seeds. Eight miRNA-target modules display contrasting expressions amongst SN and LGR, while 26 (SN) and 43 (LGR) modules are differentially expressed in all stages.

CONCLUSIONS

Integration of all analyses concludes in a "Domino effect" model for GS regulation highlighting chronology and fruition of each event. This study delineates the essence of GS regulation, providing scope for future exploits. The rice grain development database (RGDD) ( www.nipgr.ac.in/RGDD/index.php ; https://doi.org/10.5281/zenodo.7762870 ) has been developed for easy access of data generated in this paper.

Genetic Localization and Homologous Genes Mining for Barley Grain Size

Grain size is an important agronomic trait determining barley yield and quality. An increasing number of QTLs (quantitative trait loci) for grain size have been reported due to the improvement in genome sequencing and mapping. Elucidating the molecular mechanisms underpinning barley grain size is vital for producing elite cultivars and accelerating breeding processes. In this review, we summarize the achievements in the molecular mapping of barley grain size over the past two decades, highlighting the results of QTL linkage analysis and genome-wide association studies. We discuss the QTL hotspots and predict candidate genes in detail. Moreover, reported homologs that determine the seed size clustered into several signaling pathways in model plants are also listed, providing the theoretical basis for mining genetic resources and regulatory networks of barley grain size.

TaMADS29 interacts with TaNF-YB1 to synergistically regulate early grain development in bread wheat

Grain development is a crucial determinant of yield and quality in bread wheat (Triticum aestivum L.). However, the regulatory mechanisms underlying wheat grain development remain elusive. Here we report how TaMADS29 interacts with TaNF-YB1 to synergistically regulate early grain development in bread wheat. The tamads29 mutants generated by CRISPR/Cas9 exhibited severe grain filling deficiency, coupled with excessive accumulation of reactive oxygen species (ROS) and abnormal programmed cell death that occurred in early developing grains, while overexpression of TaMADS29 increased grain width and 1,000-kernel weight. Further analysis revealed that TaMADS29 interacted directly with TaNF-YB1; null mutation in TaNF-YB1 caused grain developmental deficiency similar to tamads29 mutants. The regulatory complex composed of TaMADS29 and TaNF-YB1 exercises its possible function that inhibits the excessive accumulation of ROS by regulating the genes involved in chloroplast development and photosynthesis in early developing wheat grains and prevents nucellar projection degradation and endosperm cell death, facilitating transportation of nutrients into the endosperm and wholly filling of developing grains. Collectively, our work not only discloses the molecular mechanism of MADS-box and NF-Y TFs in facilitating bread wheat grain development, but also indicates that caryopsis chloroplast might be a central regulator of grain development rather than merely a photosynthesis organelle. More importantly, our work offers an innovative way to breed high-yield wheat cultivars by controlling the ROS level in developing grains.

Genome-Wide Identification of MIKCc-Type MADS-Box Family Gene and Floral Organ Transcriptome Characterization in Ma Bamboo (Dendrocalamus latiflorus Munro)

Most bamboos die after flowering, and the molecular mechanisms responsible for flowering is poorly understood. The MIKCc-type MADS-box family gene is involved in the flowering process. To explore the mechanism of the MIKCc-type MADS-box gene and phytohormone regulation in the flowering of Dendrocalamus latiflorus Munro (D. latiflorus), characterized by extremely rapid growth and widely cultivated woody bamboo, we initially did a genome-wide analysis of the MIKCc-type MADS-box gene in D. latiflorus. In the meantime, transcriptome analysis was performed using the floral organs. A total of 170 MIKCc-Type MADS-Box genes were identified and divided into 15 categories. The cis-acting element analysis in promoters regions revealed that MIKC-type MADS-box family genes were associated with hormones, including auxin, abscisic acid (ABA), gibberellin (GA) and jasmonic acid (JA), which was found at 79, 476, 96, 486 sites and cover 61, 103, 73, 128 genes. Genome synteny analysis showed subgenome AA and BB were better than CC and obtained 49, 40, 39 synteny genes compared with Oryza sativa (O. sativa). In transcriptome analysis of floral organs, the enriched pathway from DEGs included circadian, vernalization and gibberellin pathways associated with the flowering process. We found that the jasmonic acid synthesis gene is highly expressed in the pistil, which may be the cause of Ma bamboo pollen abortion. The expression profile showed that most MIKC-type MADS-box genes exhibited high expression in flower organs. The consequences of this study will provide insight into the irregular flowering and low pollen counts of Ma bamboo.

A NAC-EXPANSIN module enhances maize kernel size by controlling nucellus elimination

Maize early endosperm development is initiated in coordination with elimination of maternal nucellar tissues. However, the underlying mechanisms are largely unknown. Here, we characterize a major quantitative trait locus for maize kernel size and weight that encodes an EXPANSIN gene, ZmEXPB15. The encoded β-expansin protein is expressed specifically in nucellus, and positively controls kernel size and weight by promoting nucellus elimination. We further show that two nucellus-enriched transcription factors (TFs), ZmNAC11 and ZmNAC29, activate ZmEXPB15 expression. Accordingly, these two TFs also promote kernel size and weight through nucellus elimination regulation, and genetic analyses support their interaction with ZmEXPB15. Importantly, hybrids derived from a ZmEXPB15 overexpression line have increased kernel weight, demonstrates its potential value in breeding. Together, we reveal a pathway modulating the cellular processes of maternal nucellus elimination and early endosperm development, and an approach to improve kernel weight.

Current studies of maize kernel development mostly focus on endosperm and embryo development, and little is known about the control of the nucellus tissue. Here, the authors report a NAC-EXPB15 pathway that regulate maize kernel size by modulating nucellus elimination and early endosperm development.

N6-Methyladenosine dynamic changes and differential methylation in wheat grain development

More methylation changes occur in late interval than in early interval of wheat seed development with protein and the starch synthesis-related pathway enriched in the later stages. Wheat seed development is a critical process to determining wheat yield and quality, which is controlled by genetics, epigenetics and environments. The N6-methyladenosine (m⁶A) modification is a reversible and dynamic process and plays regulatory role in plant development and stress responses. To better understand the role of m⁶A in wheat grain development, we characterized the m⁶A modification at 10 day post-anthesis (DPA), 20 DPA and 30 DPA in wheat grain development. m⁶A-seq identified 30,615, 30,326, 27,676 high confidence m⁶A peaks from the 10DPA, 20DPA, and 30DPA, respectively, and enriched at 3'UTR. There were 29,964, 29,542 and 26,834 unique peaks identified in AN0942_10d, AN0942_20d and AN0942_30d. One hundred and forty-two genes were methylated by m⁶A throughout seed development, 940 genes methylated in early grain development (AN0942_20d vs AN0942_10d), 1542 genes in late grain development (AN0942_30d vs AN0942_20d), and 1190 genes between early and late development stage (AN0942_30d vs AN0942_10d). KEGG enrichment analysis found that protein-related pathways and the starch synthesis-related pathway were significantly enriched in the later stages of seed development. Our results provide novel knowledge on m⁶A dynamic changes and its roles in wheat grain development.

OsMADS14 and NF-YB1 cooperate in the direct activation of OsAGPL2 and Waxy during starch synthesis in rice endosperm

Starch synthesis makes a dramatic contribution to the yield and nutritional value of cereal crops. Although several starch synthesis enzymes and related regulators have been reported, the underlying regulatory mechanisms of starch synthesis remain largely unknown. OsMADS14 is a FRUITFULL (FUL)-like MADS-box gene in rice (Oryza sativa). Here we show that two null mutations of OsMADS14 result in a shrunken and chalky grain phenotype. It is caused by obviously defective compound starch granules and a significantly reduced content of both total starch and amylose in the endosperm. Transcriptomic profiling analyses revealed that the loss-of-function of OsMADS14 leads to significantly downregulated expression of many core starch synthesis genes, including OsAGPL2 and Waxy. Both in vitro and in vivo assays demonstrate that the OsMADS14 protein directly binds to stretches of DNA with a CArG-box consensus in the putative regulatory regions of OsAGPL2 and Waxy. Protein-protein interaction experiments also suggest that OsMADS14 interacts with nuclear factor NF-YB1 to promote the transcription of OsAGPL2 and Waxy. Our study thus demonstrates that OsMADS14 plays an essential role in the synthesis of storage starch and provides novel insights into the underlying molecular mechanism that may be used to improve rice cultivars by molecular breeding.

Programmed Cell Death May Be Involved in the Seedless Phenotype Formation of Oil Palm

Oil palm (Elaeis guineensis Jacq.) is a well-known vegetable oil-yielding crop. Seedlessness is one of the most prominent traits in oil palm due to its low processing costs and high oil content. Nevertheless, an extensive study on molecular mechanisms regulating seedless phenotype formation in oil palm is very limited so far. In this study, stigma, style, and ovary from seedless and seeded (Tenera and Pisifera) oil palm trees were used to investigate the possible mechanism. Results showed that non-pollination resulted in no fruits, and self- and cross-pollinations resulted in seedless fruits, while boron treatment had no effect on seedless phenotype formation, implying that seedless trees have incomplete self and outcrossing incompatibility. Furthermore, the transcriptome data analysis highlighted eight programmed cell death (PCD) genes and three groups of PCD-related genes: 4-coumarate-CoA ligase (4CL), S-RNase, and MADS-box. The majority of these genes were significantly up-regulated in the stigma and style of Seedless palm trees compared to Tenera and Pisifera. In addition, the co-expression network analysis confirmed the significant correlation among these genes. Moreover, two simple sequence repeats (SSR) markers (S41 and S44) were developed to identify the seedless phenotype. The up-regulation of 4CL and MADS-box TFs activated the expression of PCD genes; on the other hand, S-RNase resulted in pollen tube RNA degradation and triggered PCD. While the link between PCD and seedless phenotype formation in oil palm has not been extensively studied to date, these findings suggest a role of PCD in pollen tube lethality, leading to double fertilization failure and the seedless phenotype.

Genome-wide identification, phylogenetic and expression pattern analysis of MADS-box family genes in foxtail millet (Setaria italica)

Foxtail millet (Setaria italica) is rich in nutrients and extremely beneficial to human health. We identified and comprehensively analyzed 89 MADS-box genes in the foxtail millet genome. According to the classification of MADS-box genes in Arabidopsis thaliana and rice, the SiMADS-box genes were divided into M-type (37) and MIKC-type (52). During evolution, the differentiation of MIKC-type MADS-box genes occurred before that of monocotyledons and dicotyledons. The SiMADS-box gene structure has undergone much differentiation, and the number of introns in the MIKC-type subfamily is much greater than that in the M-type subfamily. Analysis of gene duplication events revealed that MIKC-type MADS-box gene segmental duplication accounted for the vast majority of gene duplication events, and MIKC-type MADS-box genes played a major role in the amplification of SiMADS-box genes. Collinearity analysis showed highest collinearity between foxtail millet and maize MADS-box genes. Analysis of tissue-specific expression showed that SiMADS-box genes are highly expressed throughout the grain-filling process. Expression analysis of SiMADS-box genes under eight different abiotic stresses revealed many stress-tolerant genes, with induced expression of SiMADS33 and SiMADS78 under various stresses warranting further attention. Further, some SiMADS-box proteins may interact under external stress. This study provides insights for MADS-box gene mining and molecular breeding of foxtail millet in the future.

Construction of a Novel Female Sterility System for Hybrid Rice

The main constraints of current hybrid rice technology using male sterility (MS) are the low yield and high labor costs of hybrid rice seed (HRS) production. Therefore, there is an urgent need for innovative new hybrid rice technology. Fortunately, we discovered a unique spontaneous sporophytic female-sterile rice mutant controlled by a single recessive locus in the nucleus. Because female-sterile mutant lines cannot produce any selfed-seeds but their pollen has totally normal functions, female sterility (FS) lines may be considered ideal pollen donors to replace the female-fertile pollen donor parent lines currently used in the HRS production. In this study, a genetically engineered FS-based system was constructed to propagate a pure transgene-free FS line using a bentazon herbicide screening. Additionally, the ability of the FS + MS (FM)-line system, with mixed plantings of FS and MS lines, to produce HRS was tested. The pilot field experiment results showed that HRS of the FM-line system was more efficient compared with the conventional FS to MS strip planting control mode. Thus, this study provides new insights into genetic engineering technology and a promising strategy for the utilization of FS in hybrid rice.

Genome-wide analysis of genomic imprinting in the endosperm and allelic variation in flax

Genomic imprinting is an epigenetic phenomenon that causes biased expression of maternally and paternally inherited alleles. In flowering plants, genomic imprinting predominantly occurs in the triploid endosperm and plays a vital role in seed development. In this study, we identified 248 candidate imprinted genes including 114 maternally expressed imprinted genes (MEGs) and 134 paternally expressed imprinted genes (PEGs) in flax (Linum usitatissimum L.) endosperm using deep RNA sequencing. These imprinted genes were neither clustered in specific chromosomal regions nor well conserved among flax and other plant species. MEGs tended to be expressed specifically in the endosperm, whereas the expression of PEGs was not tissue-specific. Imprinted single nucleotide polymorphisms differentiated 200 flax cultivars into the oil flax, oil-fiber dual purpose flax and fiber flax subgroups, suggesting that genomic imprinting contributed to intraspecific variation in flax. The nucleotide diversity of imprinted genes in the oil flax subgroup was significantly higher than that in the fiber flax subgroup, indicating that some imprinted genes underwent positive selection during flax domestication from oil flax to fiber flax. Moreover, imprinted genes that underwent positive selection were related to flax functions. Thirteen imprinted genes related to flax seed size and weight were identified using a candidate gene-based association study. Therefore, our study provides information for further exploration of the function and genomic variation of imprinted genes in the flax population.

Programmed Cell Death in Developing Brachypodium distachyon Grain

The normal developmental sequence in a grass grain entails the death of several maternal and filial tissues in a genetically regulated process termed programmed cell death (PCD). The progression and molecular aspects of PCD in developing grains have been reported for domesticated species such as barley, rice, maize and wheat. Here, we report a detailed investigation of PCD in the developing grain of the wild model species Brachypodium distachyon. We detected PCD in developing Brachypodium grains using molecular and histological approaches. We also identified in Brachypodium the orthologs of protease genes known to contribute to grain PCD and surveyed their expression. We found that, similar to cereals, PCD in the Brachypodium nucellus occurs in a centrifugal pattern following anthesis. However, compared to cereals, the rate of post-mortem clearance in the Brachypodium nucellus is slower. However, compared to wheat and barley, mesocarp PCD in Brachypodium proceeds more rapidly in lateral cells. Remarkably, Brachypodium mesocarp PCD is not coordinated with endosperm development. Phylogenetic analysis suggests that barley and wheat possess more vacuolar processing enzymes that drive nucellar PCD compared to Brachypodium and rice. Our expression analysis highlighted putative grain-specific PCD proteases in Brachypodium. Combined with existing knowledge on grain PCD, our study suggests that the rate of nucellar PCD moderates grain size and that the pattern of mesocarp PCD influences grain shape.

Endoplasmic reticulum stress pathway mediates the early heat stress response of developing rice seeds

A transient heat stress occurring during early seed development in rice (Oryza sativa) reduces seed size by altering endosperm development. However, the relationship between the timing of the stress and specific developmental stage on heat sensitivity is not well-understood. To address this, we imposed a series of non-overlapping heat stress treatments and found that young seeds are most sensitive during the first two days after flowering. Temporal transcriptome analysis of developing, heat stressed (35°C) seeds during this window shows that Inositol-requiring enzyme 1 (IRE1)-mediated endoplasmic reticulum (ER) stress response and jasmonic acid (JA) pathways are the early (1-3 h) drivers of heat stress response. We propose that increased JA levels under heat stress may precede ER stress response as JA application promotes the spliced form of OsbZIP50, an ER response marker gene linked to IRE1-specific pathway. This study presents temporal and mechanistic insights into the role of JA and ER stress signalling during early heat stress response of rice seeds that impact both grain size and quality. Modulating the heat sensitivity of the early sensing pathways and downstream endosperm development genes can enhance rice resilience to transient heat stress events.

A MADS-Box Gene CiMADS43 Is Involved in Citrus Flowering and Leaf Development through Interaction with CiAGL9

MADS-box genes are involved in various developmental processes including vegetative development, flower architecture, flowering, pollen formation, seed and fruit development. However, the function of most MADS-box genes and their regulation mechanism are still unclear in woody plants compared with model plants. In this study, a MADS-box gene (CiMADS43) was identified in citrus. Phylogenetic and sequence analysis showed that CiMADS43 is a GOA-like Bsister MADS-box gene. It was localized in the nucleus and as a transcriptional activator. Overexpression of CiMADS43 promoted early flowering and leaves curling in transgenic Arabidopsis. Besides, overexpression or knockout of CiMADS43 also showed leaf curl phenotype in citrus similar to that of CiMADS43 overexpressed in Arabidopsis. Protein–protein interaction found that a SEPALLATA (SEP)-like protein (CiAGL9) interacted with CiMADS43 protein. Interestingly, CiAGL9 also can bind to the CiMADS43 promoter and promote its transcription. Expression analysis also showed that these two genes were closely related to seasonal flowering and the development of the leaf in citrus. Our findings revealed the multifunctional roles of CiMADS43 in the vegetative and reproductive development of citrus. These results will facilitate our understanding of the evolution and molecular mechanisms of MADS-box genes in citrus.

The nucellus: between cell elimination and sugar transport

The architecture of the seed is shaped by the processes of tissue partitioning, which determines the volume ratio of maternal and zygotic tissues, and nutrient partitioning, which regulates nutrient distribution among tissues. In angiosperms, early seed development is characterized by antagonistic development of the nucellus maternal tissue and the endosperm fertilization product to become the main sugar sink. This process marked the evolution of angiosperms and outlines the most ancient seed architectures. In Arabidopsis, the endosperm partially eliminates the nucellus and imports sugars from the seed coat. Here, we show that the nucellus is symplasmically connected to the chalaza, the seed nutrient unloading zone, and works as both a sugar sink and source alongside the seed coat. After fertilization, the transient nucellus accumulates starch early on and releases it in the apoplasmic space during its elimination. By contrast, the persistent nucellus exports sugars toward the endosperm through the SWEET4 hexose facilitator. Finally, we analyzed sugar metabolism and transport in the transparent testa 16 mutant, which fails to undergo nucellus cell elimination, which shed light on the coordination between tissue and nutrient partitioning. Overall, this study identifies a path of sugar transport in the Arabidopsis seed and describes a link between sugar redistribution and the nucellus cell-elimination program.

APETALA2 functions as a temporal factor together with BLADE-ON-PETIOLE2 and MADS29 to control flower and grain development in barley

Cereal grain develops from fertilised florets. Alterations in floret and grain development greatly influence grain yield and quality. Despite this, little is known about the underlying genetic control of these processes, especially in key temperate cereals such as barley and wheat. Using a combination of near-isogenic mutant comparisons, gene editing and genetic analyses, we reveal that HvAPETALA2 (HvAP2) controls floret organ identity, floret boundaries, and maternal tissue differentiation and elimination during grain development. These new roles of HvAP2 correlate with changes in grain size and HvAP2-dependent expression of specific HvMADS-box genes, including the B-sister gene, HvMADS29. Consistent with this, gene editing demonstrates that HvMADS29 shares roles with HvAP2 in maternal tissue differentiation. We also discovered that a gain-of-function HvAP2 allele masks changes in floret organ identity and grain size due to loss of barley LAXATUM.A/BLADE-ON-PETIOLE2 (HvBOP2) gene function. Taken together, we reveal novel pleiotropic roles and regulatory interactions for an AP2-like gene controlling floret and grain development in a temperate cereal.

The pineapple MADS-box gene family and the evolution of early monocot flower

Unlike the flower of the model monocot rice, which has diverged greatly from the ancestral monocot flower, the pineapple (Ananas comosus) flower is more typical of monocot flowers. Here, we identified 43 pineapple genes containing MADS-box domains, including 11 type I and 32 type II genes. RNA-seq expression data generated from five pineapple floral organs (sepals, petals, stamens, pistils, and ovules) and quantitative real-time PCR revealed tissue-specific expression patterns for some genes. We found that AcAGL6 and AcFUL1 were mainly expressed in sepals and petals, suggesting their involvement in the regulation of these floral organs. A pineapple ‘ABCDE’ model was proposed based on the phylogenetic analysis and expression patterns of MADS-box genes. Unlike rice and orchid with frequent species-specific gene duplication and subsequent expression divergence, the composition and expression of the ABCDE genes were conserved in pineapple. We also found that AcSEP1/3, AcAG, AcAGL11a/b/c, and AcFUL1 were highly expressed at different stages of fruit development and have similar expression profiles, implicating these genes’ role in fruit development and ripening processes. We propose that the pineapple flower can be used as a model for studying the ancestral form of monocot flowers to investigate their development and evolutionary history.

Orchid Bsister gene PeMADS28 displays conserved function in ovule integument development

The ovules and egg cells are well developed to be fertilized at anthesis in many flowering plants. However, ovule development is triggered by pollination in most orchids. In this study, we characterized the function of a B_sister gene, named PeMADS28, isolated from Phalaenopsis equestris, the genome-sequenced orchid. Spatial and temporal expression analysis showed PeMADS28 predominantly expressed in ovules between 32 and 48 days after pollination, which synchronizes with integument development. Subcellular localization and protein–protein interaction analyses revealed that PeMADS28 could form a homodimer as well as heterodimers with D-class and E-class MADS-box proteins. In addition, ectopic expression of PeMADS28 in Arabidopsis thaliana induced small curled rosette leaves, short silique length and few seeds, similar to that with overexpression of other species’ B_sister genes in Arabidopsis. Furthermore, complementation test revealed that PeMADS28 could rescue the phenotype of the ABS/TT16 mutant. Together, these results indicate the conserved function of B_sisterPeMADS28 associated with ovule integument development in orchid.

Silencing of an Ubiquitin Ligase Increases Grain Width and Weight in indica Rice

Many quantitative trait loci (QTLs) have been identified by molecular genetic studies which control grain size by regulating grain width, length, and/or thickness. Grain width 2 (GW2) is one such QTL that codes for a RING-type E3 ubiquitin ligase and increases grain size by regulating grain width through ubiquitin-mediated degradation of unknown substrates. A natural variation (single-nucleotide polymorphism at the 346^th position) in the functional domain-coding region of OsGW2 in japonica rice genotypes has been shown to cause an increase in grain width/weight in rice. However, this variation is absent in indica rice genotypes. In this study, we report that reduced expression of OsGW2 can alter grain size, even though natural sequence variation is not responsible for increased grain size in indica rice genotypes. OsGW2 shows high expression in seed development stages and the protein localizes to the nucleus and cytoplasm. Downregulation of OsGW2 by RNAi technology results in wider and heavier grains. Microscopic observation of grain morphology suggests that OsGW2 determines grain size by influencing both cell expansion and cell proliferation in spikelet hull. Using transcriptome analysis, upregulated genes related to grain size regulation have been identified among 1,426 differentially expressed genes in an OsGW2_RNAi transgenic line. These results reveal that OsGW2 is a negative regulator of grain size in indica rice and affects both cell number and cell size in spikelet hull.

OsbZIP76 interacts with OsNF-YBs and regulates endosperm cellularization in rice (Oryza sativa)

Following double fertilization, plant endosperm nuclei undergo syncytial divisions, followed by synchronous cellularization. Cellularization is a key event during endosperm development, but our understanding of its regulation is limited to Arabidopsis. In this study we show that OsbZIP76 regulates cellularization in rice (Oryza sativa). Activation of OsbZIP76 coincided with the initiation of cellularization, and its knockdown or knockout mutants exhibited precocious cellularization. Genes involved in endosperm development or starch biosynthesis were prematurely activated in the osbzip76 caryopsis. As a putative transcription factor, OsbZIP76 alone lacked transcriptional activation activity; however, it interacted with the nuclear factor Y (NF-Y) family transcription factors OsNF-YB9 and OsNF-YB1 in yeast and in planta. OsbZIP76 and OsNF-YB9 were predominantly expressed in the endosperm and the proteins colocalized. Seeds of osnf-yb1 and osbzip76 mutants showed reduced size and reduced apparent amylose content. The parent-of-origin-dependent expression of OsbZIP76 is variable in different rice accessions. In summary, OsbZIP76 is an endosperm-expressed imprinted gene that regulates endosperm development in rice.

Genome Wide Analysis of the Transcriptional Profiles in Different Regions of the Developing Rice Grains

BACKGROUND

Rice is an important food source for humans worldwide. Because of its nutritional and agricultural significance, a number of studies addressed various aspects of rice grain development and grain filling. Nevertheless, the molecular processes underlying grain filling and development, and in particular the contributions of different grain tissues to these processes, are not understood.

MAIN TEXT

Using RNA-sequencing, we profiled gene expression activity in grain tissues comprised of cross cells (CC), the nucellar epidermis (NE), ovular vascular trace (OVT), endosperm (EN) and the aleurone layer (AL). These tissues were dissected using laser capture microdissection (LCM) at three distinct grain development stages. The mRNA expression datasets offer comprehensive and new insights into the gene expression patterns in different rice grain tissues and their contributions to grain development. Comparative analysis of the different tissues revealed their similar and/or unique functions, as well as the spatio-temporal regulation of common and tissue-specific genes. The expression patterns of genes encoding hormones and transporters indicate an important role of the OVT tissue in metabolite transport during grain development. Gene co-expression network prediction on OVT-specific genes identified several distinct and common development-specific transcription factors. Further analysis of enriched DNA sequence motifs proximal to OVT-specific genes revealed known and novel DNA sequence motifs relevant to rice grain development.

CONCLUSION

Together, the dataset of gene expression in rice grain tissues is a novel and useful resource for further work to dissect the molecular and metabolic processes during rice grain development.

Pretty crowds are happy crowds: the influence of attractiveness on mood perception

Empirical findings predominantly support a happiness superiority effect in visual search and emotion categorization paradigms and reveal that social cues, like sex and race, moderate this advantage. A more recent study showed that the facial attribute attractiveness also influences the accuracy and speed of emotion perception. In the current study, we investigated whether the influence of attractiveness on emotion perception translates into a more general evaluation of moods when more than one emotional target is presented. In two experiments, we used the mood-of-the-crowd (MoC) task to investigate whether attractive crowds are perceived more positively compared to less attractive crowds. The task was to decide whether an array of faces included more angry or more happy faces. Furthermore, we recorded gaze movements to test the assumption that fixations on happy expressions occur more often in attractive crowds. Thirty-four participants took part in experiment 1 as well as in experiment 2. In both experiments, crowds presenting attractive faces were judged as being happy more frequently whereas the reverse pattern was found for unattractive crowds of faces. Moreover, participants were faster and more accurate when evaluating attractive crowds containing more happy faces as well as when judging unattractive crowds composed of more angry expressions. Additionally, in experiment 1, there were more fixations on happy compared to angry expressions in attractive crowds. Overall, the present findings support the assumption that attractiveness moderates emotion perception.

Genome-wide analysis of Jatropha curcas MADS-box gene family and functional characterization of the JcMADS40 gene in transgenic rice

Background

Physic nut (Jatropha curcas), an inedible oilseed plant, is among the most promising alternative energy sources because of its high oil content, rapid growth and extensive adaptability. Proteins encoded by MADS-box family genes are important transcription factors participated in regulating plant growth, seed development and responses to abiotic stress. However, there has been no in-depth research on the MADS-box genes and their roles in physic nut.

Results

In our study, 63 MADS-box genes (JcMADSs) were identified in the physic nut genome, and classed into five groups (MIKC^C, Mα, Mβ, Mγ, MIKC*) according to phylogenetic comparison with Arabidopsis homologs. Expression profile analysis based on RNA-seq suggested that many JcMADS genes had the strongest expression in seeds, and seven of them responded in leaves to at least one abiotic stressor (drought and/or salinity) at one or more time points. Transient expression analysis and a transactivation assay indicated that JcMADS40 is a nucleus-localized transcriptional activator. Plants overexpressing JcMADS40 did not show altered plant growth, but the overexpressing plants did exhibit reductions in grain size, grain length, grain width, 1000-seed weight and yield per plant. Further data on the reduced grain size in JcMADS40-overexpressing plants supported the putative role of JcMADS genes in seed development.

Conclusions

This study will be useful in order to further understand the process of MADS-box genes involved in regulating growth and development in addition to their functions in abiotic stress resistance, and will eventually provide a theoretical basis for the functional investigation and the exploitation of candidate genes for the molecular improvement of physic nut.

Quantitative Trait Loci for Seed Size Variation in Cucurbits - A Review

Cucurbits (Cucurbitaceae family) include many economically important fruit vegetable crops such as watermelon, pumpkin/squash, cucumber, and melon. Seed size (SS) is an important trait in cucurbits breeding, which is controlled by quantitative trait loci (QTL). Recent advances have deciphered several signaling pathways underlying seed size variation in model plants such as Arabidopsis and rice, but little is known on the genetic basis of SS variation in cucurbits. Here we conducted literature review on seed size QTL identified in watermelon, pumpkin/squash, cucumber and melon, and inferred 14, 9 and 13 consensus SS QTL based on their physical positions in respective draft genomes. Among them, four from watermelon (ClSS2.2, ClSS6.1, ClSS6.2, and ClSS8.2), two from cucumber (CsSS4.1 and CsSS5.1), and one from melon (CmSS11.1) were major-effect, stable QTL for seed size and weight. Whole genome sequence alignment revealed that these major-effect QTL were located in syntenic regions across different genomes suggesting possible structural and functional conservation of some important genes for seed size control in cucurbit crops. Annotation of genes in the four watermelon consensus SS QTL regions identified genes that are known to play important roles in seed size control including members of the zinc finger protein and the E3 ubiquitin-protein ligase families. The present work highlights the utility of comparative analysis in understanding the genetic basis of seed size variation, which may help future mapping and cloning of seed size QTL in cucurbits.

Genome-wide analysis of MIKC-type MADS-box genes in wheat: pervasive duplications, functional conservation and putative neofunctionalization

Wheat (Triticum aestivum) is one of the most important crops worldwide. Given a growing global population coupled with increasingly challenging cultivation conditions, facilitating wheat breeding by fine-tuning important traits is of great importance. MADS-box genes are prime candidates for this, as they are involved in virtually all aspects of plant development. Here, we present a detailed overview of phylogeny and expression of 201 wheat MIKC-type MADS-box genes. Homoeolog retention is significantly above the average genome-wide retention rate for wheat genes, indicating that many MIKC-type homoeologs are functionally important and not redundant. Gene expression is generally in agreement with the expected subfamily-specific expression pattern, indicating broad conservation of function of MIKC-type genes during wheat evolution. We also found extensive expansion of some MIKC-type subfamilies, especially those potentially involved in adaptation to different environmental conditions like flowering time genes. Duplications are especially prominent in distal telomeric regions. A number of MIKC-type genes show novel expression patterns and respond, for example, to biotic stress, pointing towards neofunctionalization. We speculate that conserved, duplicated and neofunctionalized MIKC-type genes may have played an important role in the adaptation of wheat to a diversity of conditions, hence contributing to the importance of wheat as a global staple food.

Genome-wide identification and expression profile of the MADS-box gene family in Erigeron breviscapus

The MADS-box gene family encodes transcription factors with many biological functions that extensively regulate plant growth, development and reproduction. Erigeron breviscapus is a medicinal herb used widely in traditional Chinese medicine, and is believed to improve blood circulation and ameliorate platelet coagulation. In order to gain a detailed understanding of how transcription factor expression may regulate the growth of this potentially important medicinal plant, a genome-wide analysis of the MADS-box gene family of E. breviscapus is needed. In the present study, 44 MADS-box genes were identified in E. breviscapus and categorized into five subgroups (MIKC, Mα, Mβ, Mγ and Mδ) according to their phylogenetic relationships with the Arabidopsis MADS-box genes. Additionally, the functional domain, subcellular location and motif compositions of the E. breviscapus MADS-box gene products were characterized. The expression levels for each of the E. breviscapus MADS-box (EbMADS) genes were analyzed in flower, leaf, stem and root organs, and showed that the majority of EbMADS genes were expressed in flowers. Meanwhile, some MADS genes were found to express high levels in leaf, stem and root, indicating that the MADS-box genes are involved in various aspects of the physiological and developmental processes of the E. breviscapus. The results from gene expression analysis under different pollination treatments revealed that the MADS-box genes were highly expressed after non-pollinated treatment. To the best of our knowledge, this study describes the first genome-wide analysis of the E. breviscapus MADS-box gene family, and the results provide valuable information for understanding of the classification, cloning and putative functions of the MADS-box family.

OsMADS18, a membrane-bound MADS-box transcription factor, modulates plant architecture and the abscisic acid response in rice

The APETALA1 (AP1)/FRUITFULL (FUL)-like transcription factor OsMADS18 plays diverse functions in rice development, but the underlying molecular mechanisms are far from fully understood. Here, we report that down-regulation of OsMADS18 expression in RNAi lines caused a delay in seed germination and young seedling growth, whereas the overexpression of OsMADS18 produced plants with fewer tillers. In targeted OsMADS18 genome-edited mutants (osmads18-cas9), an increased number of tillers, altered panicle size, and reduced seed setting were observed. The EYFP-OsMADS18 (full-length) protein was localized to the nucleus and plasma membrane but the EYFP-OsMADS18-N (N-terminus) protein mainly localized to the nucleus. The expression of OsMADS18 could be stimulated by abscisic acid (ABA), and ABA stimulation triggered the cleavage of HA-OsMADS18 and the translocation of OsMADS18 from the plasma membrane to the nucleus. The inhibitory effect of ABA on seedling growth was less effective in the OsMADS18-overexpressing plants. The expression of a set of ABA-responsive genes was significantly reduced in the overexpressing plants. The phenotypes of transgenic plants expressing EYFP-OsMADS18-N resembled those observed in the osmads18-cas9 mutants. Analysis of the interaction of OsMADS18 with OsMADS14, OsMADS15, and OsMADS57 strongly suggests an essential role for OsMADS18 in rice development.

A Dead Gene Walking: Convergent Degeneration of a Clade of MADS-Box Genes in Crucifers

Genes are "born," and eventually they "die." These processes shape the phenotypic evolution of organisms and are hence of great biological interest. If genes die in plants, they generally do so quite rapidly. Here, we describe the fate of GOA-like genes that evolve in a dramatically different manner. GOA-like genes belong to the subfamily of Bsister genes of MIKC-type MADS-box genes. Typical MIKC-type genes encode conserved transcription factors controlling plant development. We show that ABS-like genes, a clade of Bsister genes, are indeed highly conserved in crucifers (Brassicaceae) maintaining the ancestral function of Bsister genes in ovule and seed development. In contrast, their closest paralogs, the GOA-like genes, have been undergoing convergent gene death in Brassicaceae. Intriguingly, erosion of GOA-like genes occurred after millions of years of coexistence with ABS-like genes. We thus describe Delayed Convergent Asymmetric Degeneration, a so far neglected but possibly frequent pattern of duplicate gene evolution that does not fit classical scenarios. Delayed Convergent Asymmetric Degeneration of GOA-like genes may have been initiated by a reduction in the expression of an ancestral GOA-like gene in the stem group of Brassicaceae and driven by dosage subfunctionalization. Our findings have profound implications for gene annotations in genomics, interpreting patterns of gene evolution and using genes in phylogeny reconstructions of species.

Genetic and Molecular Control of Floral Organ Identity in Cereals

Grasses represent a major family of monocots comprising mostly cereals. When compared to their eudicot counterparts, cereals show a remarkable morphological diversity. Understanding the molecular basis of floral organ identity and inflorescence development is crucial to gain insight into the grain development for yield improvement purposes in cereals, however, the exact genetic mechanism of floral organogenesis remains elusive due to their complex inflorescence architecture. Extensive molecular analyses of Arabidopsis and other plant genera and species have established the ABCDE floral organ identity model. According to this model, hierarchical combinatorial activities of A, B, C, D, and E classes of homeotic genes regulate the identity of different floral organs with partial conservation and partial diversification between eudicots and cereals. Here, we review the developmental role of A, B, C, D, and E gene classes and explore the recent advances in understanding the floral development and subsequent organ specification in major cereals with reference to model plants. Furthermore, we discuss the evolutionary relationships among known floral organ identity genes. This comparative overview of floral developmental genes and associated regulatory factors, within and between species, will provide a thorough understanding of underlying complex genetic and molecular control of flower development and floral organ identity, which can be helpful to devise innovative strategies for grain yield improvement in cereals.

Asymmetric birth and death of type I and type II MADS-box gene subfamilies in the rubber tree facilitating laticifer development

The rubber tree (Hevea brasiliensis Muell. Arg.) is a rubber producing crop and contains specialized laticifers. MADS-box genes are a family of transcription factor genes that regulate plant development, especially floral organ and gametophyte development. 97 MADS-box genes were identified in the rubber tree through transcriptomes and genome mining. 93.8% of the genes were mapped onto the genome scaffolds in correspondence to the coverage (93.8%) of current version of sequenced genome. Phylogenetic analysis indicates that type II MADS-box genes have been more actively duplicated than their orthologous genes in Arabidopsis and rice, so that most (70, 72.2%) of the MADS-box genes in the rubber tree belong to type II subfamily. This is a high percentage compared to those in Arabidopsis (43.7%) and rice (56.8%). Moreover, 69 out of 70 type II genes in the rubber tree are transcribed, and they are mostly predominantly expressed in flowers, but some genes are predominantly expressed in laticifers, suggesting their roles in both flower and laticifer development. The number of type I genes in the rubber tree is only 27 (27.8%), a much smaller number compared to their orthologous genes in Arabidopsis (56.3%) and rice (43.2%). At the same time, most of the type I genes (55.6%, 15) in the rubber tree are silent and are probably pseudogenes. The high birth rate and low death rate of type II genes and low birth rate and high death rate of type I genes may corresponds to special developmental requirements in the rubber tree, e.g. the development of laticifer system for biosynthesis of cis-polyisoprene, the rubber. Moreover, atypical MIKC* factors (e.g. HbMADS1 in S-clade, and HbMADS20 in P-clade) are identified. These genes are diverged to typical MIKC* genes in sequences and facilitate functions required in laticifer development and rubber biosynthesis, which is not necessary in Arabidopsis and rice.

Diversification of the Homeotic AP3 Clade MADS-Box Genes in Asteraceae Species Chrysanthemum morifolium L. and Helianthus annuus L

The structure and phylogeny of MADS-box genes HAM91 of sunflower (Helianthus annuus) and CDM115 of chrysanthemum (Chrysanthemum morifolium) were characterized. It is shown that these genes encode MADS-domain transcription factors, which are orthologs of TM6 (Solanum lycopersicum) and APETALA3 (Arabidopsis thaliana), respectively. We obtained two types of transgenic tobacco plants (Nicotiana tabacum) with constitutive expression of HAM91 and CDM115 genes. Both types of plants flowered later than the control plants and formed more flowers and seed pods. The weight of seeds of 35S::CDM115 plants was significantly lower than in the control and 35S::HAM91 plants, which may indicate to a change in the identity of ovules in 35S::CDM115.

Seed tissue and nutrient partitioning, a case for the nucellus

Flowering plants display a large spectrum of seed architectures. The volume ratio of maternal versus zygotic seed tissues changes considerably among species and underlies different nutrient-storing strategies. Such diversity arose through the evolution of cell elimination programs that regulate the relative growth of one tissue over another to become the major storage compartment. The elimination of the nucellus maternal tissue is regulated by developmental programs that marked the origin of angiosperms and outlined the most ancient seed architectures. This review focuses on such a defining mechanism for seed evolution and discusses the role of nucellus development in seed tissues and nutrient partitioning at the light of novel discoveries on its molecular regulation.

FLOURY SHRUNKEN ENDOSPERM1 Connects Phospholipid Metabolism and Amyloplast Development in Rice

Starch synthesized and stored in amyloplasts serves as the major energy storage molecule in cereal endosperm. To elucidate the molecular mechanisms underlying amyloplast development and starch synthesis, we isolated a series of floury endosperm mutants in rice (Oryza sativa). We identified the rice mutant floury shrunken endosperm1 (fse1), which exhibited obvious defects in the development of compound starch grains, decreased starch content, and altered starch physicochemical features. Map-based cloning showed that FSE1 encodes a phospholipase-like protein homologous to phosphatidic acid-preferring phospholipase A₁FSE1 was expressed ubiquitously with abundant levels observed in developing seeds and roots. FSE1 was localized to both the cytosol and intracellular membranes. Lipid profiling indicated that total extra-plastidic lipids and phosphatidic acid were increased in fse1 plants, suggesting that FSE1 may exhibit in vivo phospholipase A₁ activity on phosphatidylcholine, phosphatidylinositol, phosphatidyl-Ser, phosphatidylethanolamine, and, in particular, phosphatidic acid. Additionally, the total galactolipid content in developing fse1 endosperm was significantly reduced, which may cause abnormal amyloplast development. Our results identify FSE1 as a phospholipase-like protein that controls the synthesis of galactolipids in rice endosperm and provide a novel connection between lipid metabolism and starch synthesis in rice grains during endosperm development.

Dissecting the role of MADS-box genes in monocot floral development and diversity

Many monocot plants have high social and economic value. These include grasses such as rice (Oryza sativa), wheat (Triticum aestivum), and barley (Hordeum vulgare), which produce soft commodities for many food and beverage industries, and ornamental flowers such ase lily (Lilium longiflorum) and orchid (Oncidium Gower Ramsey), which represent an important component of international flower markets. There is constant pressure to improve the development and diversity of these species, with a significant emphasis on flower development, and this is particularly relevant considering the impact of changing environments on reproduction and thus yield. MADS-box proteins are a family of transcription factors that contain a conserved 60 amino acid MADS-box motif. In plants, attention has been devoted to characterization of this family due to their roles in inflorescence and flower development, which holds promise for the modification of floral architecture for plant breeding. This has been explored in diverse angiosperms, but particularly the dicot model Arabidopsis thaliana. The focus of this review is on the less well characterized roles of the MADS-box proteins in monocot flower development and how changes in MADS-box proteins throughout evolution may have contributed to creating a diverse range of flowers. Examining these changes within the monocots can identify the importance of certain genes and pinpoint those which might be useful in future crop improvement and breeding strategies.

Suppression of OsMADS7 in rice endosperm stabilizes amylose content under high temperature stress

High temperature significantly alters the amylose content of rice, resulting in mature grains with poor eating quality. However, only few genes and/or quantitative trait loci involved in this process have been isolated and the molecular mechanisms of this effect remain unclear. Here, we describe a floral organ identity gene, OsMADS7, involved in stabilizing rice amylose content at high temperature. OsMADS7 is greatly induced by high temperature at the early filling stage. Constitutive suppression of OsMADS7 stabilizes amylose content under high temperature stress but results in low spikelet fertility. However, rice plants with both stable amylose content at high temperature and normal spikelet fertility can be obtained by specifically suppressing OsMADS7 in endosperm. GBSSI is the major enzyme responsible for amylose biosynthesis. A low filling rate and high expression of GBSSI were detected in OsMADS7 RNAi plants at high temperature, which may be correlated with stabilized amylose content in these transgenic seeds under high temperature. Thus, specific suppression of OsMADS7 in endosperm could improve the stability of rice amylose content at high temperature, and such transgenic materials may be a valuable genetic resource for breeding rice with elite thermal resilience.

Global transcriptome analysis and identification of genes involved in nutrients accumulation during seed development of rice tartary buckwheat (Fagopyrum Tararicum)

Tartary buckwheat seeds are rich in various nutrients, such as storage proteins, starch, and flavonoids. To get a good knowledge of the transcriptome dynamics and gene regulatory mechanism during the process of seed development and nutrients accumulation, we performed a comprehensive global transcriptome analysis using rice tartary buckwheat seeds at different development stages, namely pre-filling stage, filling stage, and mature stage. 24 819 expressed genes, including 108 specifically expressed genes, and 11 676 differentially expressed genes (DEGs) were identified. qRT-PCR analysis was performed on 34 DEGs to validate the transcriptome data, and a good consistence was obtained. Based on their expression patterns, the identified DEGs were classified to eight clusters, and the enriched GO items in each cluster were analyzed. In addition, 633 DEGs related to plant hormones were identified. Furthermore, genes in the biosynthesis pathway of nutrients accumulation were analyzed, including 10, 20, and 23 DEGs corresponding to the biosynthesis of seed storage proteins, flavonoids, and starch, respectively. This is the first transcriptome analysis during seed development of tartary buckwheat. It would provide us a comprehensive understanding of the complex transcriptome dynamics during seed development and gene regulatory mechanism of nutrients accumulation.

Analysis of MADS-Box Gene Family Reveals Conservation in Floral Organ ABCDE Model of Moso Bamboo (Phyllostachys edulis)

Mini chromosome maintenance 1, agamous, deficiens, and serum response factor (MADS)-box genes are transcription factors which play fundamental roles in flower development and regulation of floral organ identity. However, till date, identification and functions of MADS-box genes remain largely unclear in Phyllostachys edulis. In view of this, we performed a whole-genome survey and identified 34 MADS-box genes in P. edulis, and based on phylogeny, they were classified as MIKCC, MIKC∗, Mα, and Mβ. The detailed analysis about gene structure and motifs, phylogenetic classification, comparison of gene divergence and duplication are provided. Interestingly, expression patterns for most genes were found similar to those of Arabidopsis and rice, indicating that the well-established ABCDE model can be applied to P. edulis. Moreover, we overexpressed PheMADS15, an AP1-like gene, in Arabidopsis, and found that the transgenic plants have early flowering phenotype, suggesting that PheMADS15 might be a regulator of flowering transition in P. edulis. Taken together, this study provides not only insightful comprehension but also useful information for understanding the functions of MADS-box genes in P. edulis.

Dying to live: cell elimination as a developmental strategy in angiosperm seeds

The complete elimination of unwanted cells during development is a repeated theme in both multicellular animals and in plants. In plants, such events have been extensively studied and reviewed in terms of their molecular regulation, of marker genes and proteins expressed, and in terms of cellular changes associated with their progression. This review will take a slightly different view of developmental cell elimination and will concentrate specifically on the numerous elimination events that occur during ovule and seed development (here grouped together as seed development). It asks why this cell elimination occurs in specific seed tissues, in order to understand something about the commonalities underlying how seemingly disparate events are triggered and regulated. Finally, by placing the seed in its broader evolutionary context, the question of why cell elimination may have emerged as such a key component of the seed developmental toolbox will be considered.

The MADS Box Genes ABS, SHP1, and SHP2 Are Essential for the Coordination of Cell Divisions in Ovule and Seed Coat Development and for Endosperm Formation in Arabidopsis thaliana

Seed formation is a pivotal process in plant reproduction and dispersal. It begins with megagametophyte development in the ovule, followed by fertilization and subsequently coordinated development of embryo, endosperm, and maternal seed coat. Two closely related MADS-box genes, SHATTERPROOF 1 and 2 (SHP1 and SHP2) are involved in specifying ovule integument identity in Arabidopsis thaliana. The MADS box gene ARABIDOPSIS BSISTER (ABS or TT16) is required, together with SEEDSTICK (STK) for the formation of endothelium, part of the seed coat and innermost tissue layer formed by the maternal plant. Little is known about the genetic interaction of SHP1 and SHP2 with ABS and the coordination of endosperm and seed coat development. In this work, mutant and expression analysis shed light on this aspect of concerted development. Triple tt16 shp1 shp2 mutants produce malformed seedlings, seed coat formation defects, fewer seeds, and mucilage reduction. While shp1 shp2 mutants fail to coordinate the timely development of ovules, tt16 mutants show less peripheral endosperm after fertilization. Failure in coordinated division of the innermost integument layer in early ovule stages leads to inner seed coat defects in tt16 and tt16 shp1 shp2 triple mutant seeds. An antagonistic action of ABS and SHP1/SHP2 is observed in inner seed coat layer formation. Expression analysis also indicates that ABS represses SHP1, SHP2, and FRUITFUL expression. Our work shows that the evolutionary conserved Bsister genes are required not only for endothelium but also for endosperm development and genetically interact with SHP1 and SHP2 in a partially antagonistic manner.

Rice caryopsis development I: Dynamic changes in different cell layers

Rice caryopsis as one of the most important food sources for humans has a complex structure that is composed of maternal tissues including the pericarp and testa and filial tissues including the endosperm and embryo. Although rice caryopsis studies have been conducted previously, a systematic characterization throughout the entire developmental process is still lacking. In this study, detailed morphological examinations of caryopses were made during the entire 30-day developmental process. We observed some rapid changes in cell differentiation events and cataloged how cellular degeneration processes occurred in maternal tissues. The differentiations of tube cells and cross cells were achieved by 9 days after pollination (DAP). In the testa, the outer integument was degenerated by 3 DAP, while the outer layer of the inner integument degenerated by 7 DAP. In the nucellus, all tissues with the exception of the nucellar projection and the nucellar epidermis degenerated in the first 5 DAP. By 21 DAP, all maternal tissues, including vascular bundles, the nucellar projection and the nucellar epidermal cells were degenerated. In summary, this study provides a complete atlas of the dynamic changes in cell differentiation and degeneration for individual maternal cell layers of rice caryopsis.

Endosperm and Nucellus Develop Antagonistically in Arabidopsis Seeds

In angiosperms, seed architecture is shaped by the coordinated development of three genetically different components: embryo, endosperm, and maternal tissues. The relative contribution of these tissues to seed mass and nutrient storage varies considerably among species. The development of embryo, endosperm, or nucellus maternal tissue as primary storage compartments defines three main typologies of seed architecture. It is still debated whether the ancestral angiosperm seed accumulated nutrients in the endosperm or the nucellus. During evolution, plants shifted repeatedly between these two storage strategies through molecular mechanisms that are largely unknown. Here, we characterize the regulatory pathway underlying nucellus and endosperm tissue partitioning in Arabidopsis thaliana We show that Polycomb-group proteins repress nucellus degeneration before fertilization. A signal initiated in the endosperm by the AGAMOUS-LIKE62 MADS box transcription factor relieves this Polycomb-mediated repression and therefore allows nucellus degeneration. Further downstream in the pathway, the TRANSPARENT TESTA16 (TT16) and GORDITA MADS box transcription factors promote nucellus degeneration. Moreover, we demonstrate that TT16 mediates the crosstalk between nucellus and seed coat maternal tissues. Finally, we characterize the nucellus cell death program and its feedback role in timing endosperm development. Altogether, our data reveal the antagonistic development of nucellus and endosperm, in coordination with seed coat differentiation.