Gibberellic Acid: A Key Phytohormone for Spikelet Fertility in Rice Grain Production

Effect of gibberellin on crown root development in the mutant of the rice plasmodesmal Germin-like protein OsGER4

Rice is an essential but highly stress-susceptible crop, whose root system plays an important role in plant development and stress adaptation. The rice root system architecture is controlled by gene regulatory networks involving different phytohormones including auxin, jasmonate, and gibberellin. Gibberellin is generally known as a molecular clock that interacts with different pathways to regulate root meristem development. The exogenous treatment of rice plantlets with Gibberellin reduced the number of crown roots, whilst the exogenous jasmonic acid treatment enhanced them by involving a Germin-like protein OsGER4. Due to those opposite effects, this study aims to investigate the effect of Gibberellin on crown root development in the rice mutant of the plasmodesmal Germin-like protein OsGER4. Under exogenous gibberellin treatment, the number of crown roots significantly increased in osger4 mutant lines and decreased in the OsGER4 overexpressed lines. GUS staining showed that OsGER4 was strongly expressed in rice root systems, particularly crown and lateral roots under GA3 application. Specifically, OsGER4 was strongly expressed from the exodermis, epidermis, sclerenchyma to the endodermis layers of the crown root, along the vascular bundle and throughout LR primordia. The plasmodesmal protein OsGER4 is suggested to be involved in crown root development by maintaining hormone homeostasis, including Gibberillin.

Uncovering the Genomic Regions Associated with Yield Maintenance in Rice Under Drought Stress Using an Integrated Meta-Analysis Approach

The complex trait of yield is controlled by several quantitative trait loci (QTLs). Given the global water deficit issue, the development of rice varieties suitable for non-flooded cultivation holds significant importance in breeding programs. The powerful approach of Meta-QTL (MQTL) analysis can be used for the genetic dissection of complicated quantitative traits. In the current study, a comprehensive MQTL analysis was conducted to identify consistent QTL regions associated with drought tolerance and yield-related traits under water deficit conditions in rice. In total, 1087 QTLs from 134 rice populations, published between 2000 to 2021, were utilized in the analysis. Distinct MQTL analysis of the relevant traits resulted in the identification of 213 stable MQTLs. The confidence interval (CI) for the detected MQTLs was between 0.12 and 19.7 cM. The average CI of the identified MQTLs (4.68 cM) was 2.74 times narrower compared to the average CI of the initial QTLs. Interestingly, 63 MQTLs coincided with SNP peak positions detected by genome-wide association studies for yield and drought tolerance-associated traits under water deficit conditions in rice. Considering the genes located both in the QTL-overview peaks and the SNP peak positions, 19 novel candidate genes were introduced, which are associated with drought response index, plant height, panicle number, biomass, and grain yield. Moreover, an inclusive MQTL analysis was performed on all the traits to obtain "Breeding MQTLs". This analysis resulted in the identification of 96 MQTLs with a CI ranging from 0.01 to 9.0 cM. The mean CI of the obtained MQTLs (2.33 cM) was 4.66 times less than the mean CI of the original QTLs. Thirteen MQTLs fulfilling the criteria of having more than 10 initial QTLs, CI < 1 cM, and an average phenotypic variance explained greater than 10%, were designated as "Breeding MQTLs". These findings hold promise for assisting breeders in enhancing rice yield under drought stress conditions.

Gibberellin confers to the expression of TaGA-6D and negatively regulates the fertility of wheat with Aegilops juvenalis cytoplasm

As the trace signal molecules widely existing in plants, plant hormones can regulate physiological responses of plants at low concentrations. At present, the effect of plant endogenous hormones on wheat male fertility has attracted attention, but the molecular mechanism underlying fertility regulation is unclear. Given this, the anthers of five isonuclear alloplasmic male sterile lines and their maintainer line were RNA-sequenced. A gene TaGA-6D encoding gibberellin (GA) regulated protein was isolated, which was located to the nucleus, cell wall and/or cell membrane, and predominantly highly expressed in the anther of Ju706A, a male sterile line with Aegilops juvenalis cytoplasm. By spraying assay of GA with different concentrations on fertility line Ju706R, it was found that with the increase of exogenous GA concentration, the content of endogenous GA and expression level of TaGA-6D in anther gradually increased, and the fertility decreased. However, silencing of TaGA-6D partially restore the fertility of Ju706R sprayed with 1000ng/μl GA, and indicating that gibberellin can promote the expression of TaGA-6D and negatively regulates the fertility of wheat with Aegilops juvenalis cytoplasm, which providing new insights for understanding hormone regulation of male fertility in wheat.

The transcription factor TaGAMYB modulates tapetum and pollen development of TGMS wheat YanZhan 4110S via the gibberellin signaling

Male reproductive development in higher plants experienced a series of complex biological processes, which can be regulated by Gibberellins (GA). The transcriptional factor GAMYB is a crucial component of GA signaling in anther development. However, the mechanism of GAMYB in wheat male reproduction is less understood. Here, we found that the thermo-sensitive genic male sterilitywheat line YanZhan 4110S displayed delayed tapetum programmed cell death and pollen abortive under the hot temperature stress. Combined with RNA-Sequencing data analysis, TaGAMYB associated with fertility conversion was isolated, which was located in the nucleus and highly expressed in fertility anthers. The silencing of TaGAMYB in wheat displayed fertility decline, defects in tapetum, pollen and exine formation, where the abortion characteristics were the same as YanZhan 4110S. In addition, either hot temperature or GA3 treatment in YanZhan 4110S caused the downregulation of TaGAMYB at binucleate stage and trinucleate stage, as well as fertility decrease. Further, the transcription factor TaWRKY2 significantly changed under GA3-treatment and directly interacted with the TaGAMYB promoter by W-box cis-element. Therefore, we suggested that TaGAMYB may be essential for anther development and male fertility, and GA3 activates TaGAMYB by TaWRKY2 to regulate fertility in wheat.

Genetic and molecular factors in determining grain number per panicle of rice

It was suggested that the most effective way to improve rice grain yield is to increase the grain number per panicle (GN) through the breeding practice in recent decades. GN is a representative quantitative trait affected by multiple genetic and environmental factors. Understanding the mechanisms controlling GN has become an important research field in rice biotechnology and breeding. The regulation of rice GN is coordinately controlled by panicle architecture and branch differentiation, and many GN-associated genes showed pleiotropic effect in regulating tillering, grain size, flowering time, and other domestication-related traits. It is also revealed that GN determination is closely related to vascular development and the metabolism of some phytohormones. In this review, we summarize the recent findings in rice GN determination and discuss the genetic and molecular mechanisms of GN regulators.

The MSI1 member OsRBAP1 gene, identified by a modified MutMap method, is required for rice height and spikelet fertility

To explore the molecular mechanisms underlying plant height regulation, we isolated and characterized a stably inherited semi-dwarf mutant bgsd-2 from the ethane methyl sulfonate (EMS) mutant progeny of 'Ping Tang Wild-type (PTWT)', a rice (Oryza sativa ssp. japonica) landrace in Guizhou. Transcriptome sequencing and qRT-PCR analyses showed that a number of cellulose and lignin-related genes involved in cell wall biogenesis were substantially downregulated in bgsd-2. MutMap-based cloning revealed the occurrence of a single amino acid substitution in the LOC_Os01g51300 gene, belonging to the MSI1 (multicopy suppressor of IRA1) member OsRBAP1. The bgsd-2 mutation occurred in the 3rd exon of OsRBAP1, resulting in a nonsense mutation of a codon shift from glycine (G) to glutamic acid (E) at residue 65. Protein localization analysis uncovered that the OsRBAP1 gene encodes a nuclear-localized protein and that the mutation in bgsd-2 may affect the stability of the OsRBAP1 protein. The CRISPR/Cas9 system was used to switch off OsRBAP1 in PTWT to obtain the knockout mutant osrbap1, which exhibited a severe reduction in height and fertility. Cytological observations suggest that the dwarfism of osrabp1 may be caused by reduced cell size and numbers, and that male sterility may be due to abnormal microspore development. Transcriptome analysis revealed that OsRBAP1 defects can repress the expression of numerous essential genes, which regulate multiple developmental processes in plants. Altogether, our results suggest that OsRBAP1 plays an important role in the regulation of rice height and spikelet fertility.

OsSWEET11b, a potential sixth leaf blight susceptibility gene involved in sugar transport-dependent male fertility

SWEETs play important roles in intercellular sugar transport. Induction of SWEET sugar transporters by Transcription Activator-Like effectors (TALe) of Xanthomonas ssp. is key for virulence in rice, cassava and cotton. We identified OsSWEET11b with roles in male fertility and potential bacterial blight (BB) susceptibility in rice. While single ossweet11a or 11b mutants were fertile, double mutants were sterile. As clade III SWEETs can transport gibberellin (GA), a key hormone for spikelet fertility, sterility and BB susceptibility might be explained by GA transport deficiencies. However, in contrast with the Arabidopsis homologues, OsSWEET11b did not mediate detectable GA transport. Fertility and susceptibility therefore are likely to depend on sucrose transport activity. Ectopic induction of OsSWEET11b by designer TALe enabled TALe-free Xanthomonas oryzae pv. oryzae (Xoo) to cause disease, identifying OsSWEET11b as a potential BB susceptibility gene and demonstrating that the induction of host sucrose uniporter activity is key to virulence of Xoo. Notably, only three of six clade III SWEETs are targeted by known Xoo strains from Asia and Africa. The identification of OsSWEET11b is relevant for fertility and for protecting rice against emerging Xoo strains that target OsSWEET11b.

The GA-DELLA-OsMS188 module controls male reproductive development in rice

Pollen protects male sperm and allows flowering plants to adapt to diverse terrestrial environments, thereby leading to the rapid expansion of plants into new regions. The process of anther/pollen development is coordinately regulated by internal and external factors including hormones. Currently, the molecular mechanisms underlying gibberellin (GA)-mediated male reproductive development in plants remain unknown. We show here that rice DELLA/SLR1, which encodes the central negative regulator of GA signaling, is essential for rice anther development. The slr1-5 mutant exhibits premature programmed cell death of the tapetum, lacks Ubisch bodies, and has no exine and no mature pollen. SLR1 is mainly expressed in tapetal cells and tetrads, and is required for the appropriate expression of genes encoding key factors of pollen development, which are suggested to be OsMS188-targeted genes. OsMS188 is the main component in the essential genetic program of tapetum and pollen development. Further, we demonstrate that SLR1 interacts with OsMS188 to cooperatively activate the expression of the sporopollenin biosynthesis and transport-related genes CYP703A3, DPW, ABCG15 and PKS1 for rapid formation of pollen walls. Overall, the results of this study suggest that the GA hormonal signal is integrated into the anther genetic program and regulates rice anther development through the GA-DELLA-OsMS188 module.

OsBIC1 Directly Interacts with OsCRYs to Regulate Leaf Sheath Length through Mediating GA-Responsive Pathway

Cryptochrome 1 and 2 (CRY1 and CRY2) are blue light receptors involved in the regulation of hypocotyl elongation, cotyledon expansion, and flowering time in Arabidopsisthaliana. Two cryptochrome-interacting proteins, Blue-light Inhibitor of Cryptochrome 1 and 2 (BIC1 and BIC2), have been found in Arabidopsis. BIC1 plays critical roles in suppressing the physiological activities of CRY2, which include the blue light-dependent dimerization, phosphorylation, photobody formation, and degradation process, but the functional characterization of BIC protein in other crops has not yet been performed. To investigate the function of BIC protein in rice (Oryza sativa), two homologous genes of Arabidopsis BIC1 and BIC2, namely OsBIC1 and OsBIC2 (OsBICs), were identified. The overexpression of OsBIC1 and OsBIC2 led to increased leaf sheath length, whereas mutations in OsBIC1 displayed shorter leaf sheath in a blue light intensity-dependent manner. OsBIC1 regulated blue light-induced leaf sheath elongation through direct interaction with OsCRY1a, OsCRY1b, and OsCRY2 (OsCRYs). Longitudinal sections of the second leaf sheath demonstrated that OsBIC1 and OsCRYs controlled leaf sheath length by influencing the ratio of epidermal cells with different lengths. RNA-sequencing (RNA-seq) and quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) analysis further proved that OsBIC1 and OsCRYs regulated similar transcriptome changes in regulating Gibberellic Acids (GA)-responsive pathway. Taken together, these results suggested that OsBIC1 and OsCRYs worked together to regulate epidermal cell elongation and control blue light-induced leaf sheath elongation through the GA-responsive pathway.

Mechanisms of elevated CO2-induced thermotolerance in plants: the role of phytohormones

Rising atmospheric CO₂ is a key driver of climate change, intensifying drastic changes in meteorological parameters. Plants can sense and respond to changes in environmental parameters including atmospheric CO₂ and temperatures. High temperatures beyond the physiological threshold can significantly affect plant growth and development and thus attenuate crop productivity. However, elevated atmospheric CO₂ can mitigate the deleterious effects of heat stress on plants. Despite a large body of literature supporting the positive impact of elevated CO₂ on thermotolerance, the underlying biological mechanisms and precise molecular pathways that lead to enhanced tolerance to heat stress remain largely unclear. Under heat stress, elevated CO₂-induced expression of respiratory burst oxidase homologs (RBOHs) and reactive oxygen species (ROS) signaling play a critical role in stomatal movement, which optimizes gas exchange to enhance photosynthesis and water use efficiency. Notably, elevated CO₂ also fortifies antioxidant defense and redox homeostasis to alleviate heat-induced oxidative damage. Both hormone-dependent and independent pathways have been shown to mediate high CO₂-induced thermotolerance. The activation of heat-shock factors and subsequent expression of heat-shock proteins are thought to be the essential mechanism downstream of hormone and ROS signaling. Here we review the role of phytohormones in plant response to high atmospheric CO₂ and temperatures. We also discuss the potential mechanisms of elevated CO₂-induced thermotolerance by focusing on several key phytohormones such as ethylene. Finally, we address some limitations of our current understanding and the need for further research to unveil the yet-unknown crosstalk between plant hormones in mediating high CO₂-induced thermotolerance in plants.

Genetic and Molecular Factors Determining Grain Weight in Rice

Grain weight is one of the major factors determining single plant yield production of rice and other cereal crops. Research has begun to reveal the regulatory mechanisms underlying grain weight as well as grain size, highlighting the importance of this research for plant molecular biology. The developmental trait of grain weight is affected by multiple molecular and genetic aspects that lead to dynamic changes in cell division, expansion and differentiation. Additionally, several important biological pathways contribute to grain weight, such as ubiquitination, phytohormones, G-proteins, photosynthesis, epigenetic modifications and microRNAs. Our review integrates early and more recent findings, and provides future perspectives for how a more complete understanding of grain weight can optimize strategies for improving yield production. It is surprising that the acquired wealth of knowledge has not revealed more insights into the underlying molecular mechanisms. To accelerating molecular breeding of rice and other cereals is becoming an emergent and critical task for agronomists. Lastly, we highlighted the importance of leveraging gene editing technologies as well as structural studies for future rice breeding applications.

Genome-wide analysis and functional characterization of the DELLA gene family associated with stress tolerance in B. napus

BACKGROUND

Brassica napus is an essential crop for oil and livestock feed. Eventually, this crop's economic interest is at the most risk due to anthropogenic climate change. DELLA proteins constitute a significant repressor of plant growth to facilitate survival under constant stress conditions. DELLA proteins lack DNA binding domain but can interact with various transcription factors or transcription regulators of different hormonal families. Significant progress has been made on Arabidopsis and cereal plants. However, no comprehensive study regarding DELLA proteins has been delineated in rapeseed.

RESULTS

In our study, we have identified 10 BnaDELLA genes. All of the BnaDELLA genes are closely related to five AtDELLA genes, suggesting a relative function and structure. Gene duplication and synteny relationship among Brassica. napus, Arabidopsis. thaliana, Brassica rapa, Brassica oleracea, and Brassica nigra genomes were also predicted to provide valuable insights into the BnaDELLA gene family evolutionary characteristics. Chromosomal mapping revealed the uneven distribution of BnaDELLA genes on eight chromosomes, and site-specific selection assessment proposes BnaDELLA genes purifying selection. The motifs composition in all BnaDELLA genes is inconsistent; however, every BnaDELLA gene contains 12 highly conserved motifs, encoding DELLA and GRAS domains. The two known miRNAs (bna-miR6029 and bna-miR603) targets BnaC07RGA and BnaA09GAI, were also predicted. Furthermore, quantitative real-time PCR (qRT-PCR) analysis has exhibited the BnaDELLA genes diverse expression patterns in the root, mature-silique, leaf, flower, flower-bud, stem, shoot-apex, and seed. Additionally, cis-acting element prediction shows that all BnaDELLA genes contain light, stress, and hormone-responsive elements on their promoters. The gene ontology (GO) enrichment report indicated that the BnaDELLA gene family might regulate stress responses. Combine with transcriptomic data used in this study, we detected the distinct expression patterns of BnaDELLA genes under biotic and abiotic stresses.

CONCLUSION

In this study, we investigate evolution feature, genomic structure, miRNAs targets, and expression pattern of the BnaDELLA gene family in B. napus, which enrich our understanding of BnaDELLA genes in B. napus and suggests modulating individual BnaDELLA expression is a promising way to intensify rapeseed stress tolerance and harvest index.

Magnetic Ti3C2 MXene functionalized with β-cyclodextrin as magnetic solid-phase extraction and in situ derivatization for determining 12 phytohormones in oilseeds by ultra-performance liquid chromatography-tandem mass spectrometry

Magnetic solid phase extraction integrated with in situ derivations for the profiling of 12 phytohormones in a single rapeseed seed was developed by using ultra-high performance liquid chromatography-tandem mass spectrometry. The Fe₃O₄@Ti₃C₂@β-cyclodextrin nanoparticles were firstly synthesized and used as an adsorbent for the solid-phase extraction of phytohormones. The magnetic dispersive solid-phase extraction and in situ derivation by the addition of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide were ingeniously combined. This efficient pre-treatment method integrated the extraction, purification, and derivatization processes into one single step. Satisfactory methodological performance was achieved by optimization of the parameters. Linearities (R² > 0.9928) and recoveries (80.4 %-115.1%) at three spiked levels, as well as the low matrix effect (from -16.63% to 17.06%) and limits of detection (0.89-13.62 pg/mL) were obtained. The spatio-temporal profiling of target phytohormones in different tissues of rapeseed germination was investigated. This method was successfully employed for analyzing target phytohormones in different oilseeds samples.

A quantitative trait locus GW6 controls rice grain size and yield through the gibberellin pathway

Grain size is one of the essential components determining rice yield and is a target for both domestication and artificial breeding. Gibberellins (GAs) are diterpenoid phytohormones that influence diverse aspects of plant growth and development. Several quantitative trait loci (QTLs) have been identified that control grain size through phytohormone regulation. However, little is known about the role of GAs in the control of grain size. Here we report the cloning and characterization of a QTL, GW6 (GRAIN WIDTH 6), which encodes a GA-regulated GAST family protein and positively regulates grain width and weight. GW6 is highly expressed in the young panicle and increases grain width by promoting cell expansion in the spikelet hull. Knockout of GW6 exhibits reduced grain size and weight, whereas overexpression of GW6 results in increased grain size and weight. GW6 is induced by GA and its knockout downregulates the expression of GA biosynthesis genes and decreases GA content in the young panicle. We found that a natural variation in the cis element CAAT-box in the promoter of GW6 is associated with its expression level and grain width and weight. Furthermore, introduction of GW6 to Oryza indica variety HJX74 can lead to a 10.44% increase in rice grain yield, indicating that GW6 has great potential to improve grain yield in rice.

Enhancement of gibberellic acid production from Fusarium fujikuroi by mutation breeding and glycerol addition

Gibberellic acid (GA₃) is a natural plant growth hormone that has been widely used in agriculture and horticulture. To obtain higher GA₃ producing strains, the method of screening the strains for resistance to simvastatin was used after treatment with nitrosoguanidine (NTG) and gamma rays. The rationale for the strategy was that mutants showing simvastatin resistance were likely to be high GA₃ producers, as their activity of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is relatively more effective. GA₃ yield of mutant S109 increased by 14.2% than that of the original strain. The GA₃ production ability in mutant S109 remained relatively stable after ten generations. With the addition of 0.4 g glycerol on the 5th day during the fermentation process in Erlenmeyer flask, maximum GA₃ production of 2.7 g/L was achieved by this mutant, exhibiting 28.6% increase compared with original strain. Furthermore, we also achieved 2.8 g/L GA₃ and had a 33.3% increase with addition 20 g glycerol on the 5th day during the fermentation process in a 5-L bioreactor. Our results indicated efficient GA₃ production could be achieved on the condition that the supply of glycerol at the suitable conditions. This study would lay a foundation for industrial production of GA₃.

A Lobularia maritima LmSAP protein modulates gibberellic acid homeostasis via its A20 domain under abiotic stress conditions

Stress-associated proteins (SAPs) are favorable targets to improve stress tolerance in plants, owing to their roles in developmental processes and stress responses. However, the role of SAPs and the molecular mechanisms by which they regulate plant stress responses remain poorly understood. Previously, it was reported that LmSAP expression was upregulated by various abiotic stressors in Lobularia maritima, and that transgenic tobacco lines with constitutively expressed LmSAPΔA20 and LmSAPΔA20-ΔAN1 showed dwarf phenotypes due to the deficiency of cell elongation under salt and osmotic stresses. In this study, we examined the function of A20 domain in the GA pathway in response to abiotic stresses. Transient expression of acGFP-LmSAPΔA20 and acGFP-LmSAPΔA20-ΔAN1 in onion epidermal cells demonstrated that these fused proteins were localized in the nucleo–cytoplasm. However, the truncated form acGFP-LmSAPΔAN1 was localized in the nucleus. Moreover, comparison of native and truncated LmSAP showed dramatic structural changes caused by the deletion of the A20 domain, leading to loss of function and localization. Interestingly, overexpression LmSAP and truncated LmSAPΔAN1 led to up-regulation of GA biosynthetic genes and increased total gibberellins (GAs) content, corresponding with accelerated development in transgenic tobacco plants. Moreover, the dwarf phenotype of the transgenic lines that express LmSAPΔA20 and LmSAPΔA20-ΔAN1 under stress conditions was fully restored by the application of exogenous GA₃. These findings improve our understanding of the role of LmSAP in regulating GA homeostasis, which is important for regulating plant development under abiotic stress conditions.

OsMYB80 Regulates Anther Development and Pollen Fertility by Targeting Multiple Biological Pathways

Pollen development is critical to the reproductive success of flowering plants, but how it is regulated is not well understood. Here, we isolated two allelic male-sterile mutants of OsMYB80 and investigated how OsMYB80 regulates male fertility in rice. OsMYB80 was barely expressed in tissues other than anthers, where it initiated the expression during meiosis, reached the peak at the tetrad-releasing stage and then quickly declined afterward. The osmyb80 mutants exhibited premature tapetum cell death, lack of Ubisch bodies, no exine and microspore degeneration. To understand how OsMYB80 regulates anther development, RNA-seq analysis was conducted to identify genes differentially regulated by OsMYB80 in rice anthers. In addition, DNA affinity purification sequencing (DAP-seq) analysis was performed to identify DNA fragments interacting with OsMYB80 in vitro. Overlap of the genes identified by RNA-seq and DAP-seq revealed 188 genes that were differentially regulated by OsMYB80 and also carried an OsMYB80-interacting DNA element in the promoter. Ten of these promoter elements were randomly selected for gel shift assay and yeast one-hybrid assay, and all showed OsMYB80 binding. The 10 promoters also showed OsMYB80-dependent induction when co-expressed in rice protoplast. Functional annotation of the 188 genes suggested that OsMYB80 regulates male fertility by directly targeting multiple biological processes. The identification of these genes significantly enriched the gene networks governing anther development and provided much new information for the understanding of pollen development and male fertility.

Diverse and dynamic roles of F-box proteins in plant biology

The SCF complex is a widely studied multi-subunit ring E3 ubiquitin ligase that tags targeted proteins with ubiquitin for protein degradation by the ubiquitin 26S-proteasome system (UPS). The UPS is an important system that generally keeps cellular events tightly regulated by purging misfolded or damaged proteins and selectively degrading important regulatory proteins. The specificity of this post-translational regulation is controlled by F-box proteins (FBPs) via selective recognition of a protein-protein interaction motif at the C-terminal domain. Hence, FBPs are pivotal proteins in determining the plant response in multiple scenarios. It is not surprising that the FBP family is one of the largest protein families in the plant kingdom. In this review, the roles of FBPs, specifically in plants, are compiled to provide insights into their involvement in secondary metabolites, plant stresses, phytohormone signalling, plant developmental processes and miRNA biogenesis.

Genome-wide and SNP network analyses reveal genetic control of spikelet sterility and yield-related traits in wheat

Revealing the genetic factors underlying yield and agronomic traits in wheat are an imperative need for covering the global food demand. Yield boosting requires a deep understanding of the genetic basis of grain yield-related traits (e.g., spikelet fertility and sterility). Here, we have detected much natural variation among ancient hexaploid wheat accessions in twenty-two agronomic traits collected over eight years of field experiments. A genome-wide association study (GWAS) using 15 K single nucleotide polymorphisms (SNPs) was applied to detect the genetic basis of studied traits. Subsequently, the GWAS output was reinforced via other statistical and bioinformatics analyses to detect putative candidate genes. Applying the genome-wide SNP-phenotype network defined the most decisive SNPs underlying the traits. Six pivotal SNPs, co-located physically within the genes encoding enzymes, hormone response, metal ion transport, and response to oxidative stress have been identified. Of these, metal ion transport and Gibberellin 2-oxidases (GA2oxs) genes showed strong involvement in controlling the spikelet sterility, which had not been reported previously in wheat. SNP-gene haplotype analysis confirmed that these SNPs influence spikelet sterility, especially the SNP co-located on the exon of the GA2ox gene. Interestingly, these genes were highly expressed in the grain and spike, demonstrating their pivotal role in controlling the trait. The integrative analysis strategy applied in this study, including GWAS, SNP-phenotype network, SNP-gene haplotype, expression analysis, and genome-wide prediction (GP), empower the identification of functional SNPs and causal genes. GP outputs obtained in this study are encouraging for the implementation of the traits to accelerate yield improvement by making an early prediction of complex yield-related traits in wheat. Our findings demonstrate the usefulness of the ancient wheat material as a valuable resource for yield-boosting. This is the first comprehensive genome-wide analysis for spikelet sterility in wheat, and the results provide insights into yield improvement.

The Ubiquitin-Binding Protein OsDSK2a Mediates Seedling Growth and Salt Responses by Regulating Gibberellin Metabolism in Rice

UBL-UBA (ubiquitin-like-ubiquitin-associated) proteins are ubiquitin receptors and transporters in the ubiquitin-proteasome system that play key roles in plant growth and development. High salinity restricts plant growth by disrupting cellular metabolism, but whether UBL-UBA proteins are involved in this process is unclear. Here, we demonstrate that the UBL-UBA protein OsDSK2a (DOMINANT SUPPRESSOR of KAR2) mediates seedling growth and salt responses in rice (Oryza sativa). Through analysis of osdsk2a, a mutant with retarded seedling growth, as well as in vitro and in vivo assays, we demonstrate that OsDSK2a combines with polyubiquitin chains and interacts with the gibberellin (GA)-deactivating enzyme ELONGATED UPPERMOST INTERNODE (EUI), resulting in its degradation through the ubiquitin-proteasome system. Bioactive GA levels were reduced, and plant growth was retarded in the osdsk2a mutant. By contrast, eui mutants displayed increased seedling growth and bioactive GA levels. OsDSK2a levels decreased in plants under salt stress. Moreover, EUI accumulated under salt stress more rapidly in osdsk2a than in wild-type plants. Thus, OsDSK2a and EUI play opposite roles in regulating plant growth under salt stress by affecting GA metabolism. Under salt stress, OsDSK2a levels decrease, thereby increasing EUI accumulation, which promotes GA metabolism and reduces plant growth.

Integrating the dynamics of yield traits in rice in response to environmental changes

Reductions in crop yields as a consequence of global climate change threaten worldwide food security. It is therefore imperative to develop high-yielding crop plants that show sustainable production under stress conditions. In order to achieve this aim through breeding or genetic engineering, it is crucial to have a complete and comprehensive understanding of the molecular basis of plant architecture and the regulation of its sub-components that contribute to yield under stress. Rice is one of the most widely consumed crops and is adversely affected by abiotic stresses such as drought and salinity. Using it as a model system, in this review we present a summary of our current knowledge of the physiological and molecular mechanisms that determine yield traits in rice under optimal growth conditions and under conditions of environmental stress. Based on physiological functioning, we also consider the best possible combination of genes that may improve grain yield under optimal as well as environmentally stressed conditions. The principles that we present here for rice will also be useful for similar studies in other grain crops.

Roles of phytohormone changes in the grain yield of rice plants exposed to heat: a review

During its reproductive phase, rice is susceptible to heat stress. Heat events will occur at all stages during the reproductive phase of rice as a result of global warming. Moreover, rice yield traits respond differently to heat stress during panicle initiation, flowering and grain filling. The reduction in the number of spikelets per panicle of heat-stressed plants is due to the attenuated differentiation of secondary branches and their attached florets as well as the promotion of their degradation during the panicle-initiation stage but is not affected by heat stress thereafter. Spikelet sterility as a result of heat stress is attributed not only to physiological abnormalities in the reproductive organs during the flowering stage but also to structural and morphological abnormalities in reproductive organs during the panicle-initiation stage. The reduced grain weight of heat-stressed plants is due to a reduction in nonstructural carbohydrates, undeveloped vascular bundles, and a reduction in glume size during the panicle-initiation stage, while a shortened grain-filling duration, reduced grain-filling rate, and decreased grain width contribute to reduced grain weight during the grain-filling stage. Thus, screening and breeding rice varieties that have comprehensive tolerance to heat stress at all time points during their reproductive stage may be possible to withstand unpredictable heat events in the future. The responses of yield traits to heat stress are regulated by phytohormone levels, which are determined by phytohormone homeostasis. Currently, the biosynthesis and transport of phytohormones are the key processes that determine phytohormone levels in and grain yield of rice under heat stress. Studies on phytohormone homeostatic responses are needed to further reveal the key processes that determine phytohormone levels under heat conditions.

Cold-Induced Male Meiotic Restitution in Arabidopsis thaliana Is Not Mediated by GA-DELLA Signaling

Short periods of cold stress induce male meiotic restitution and diploid pollen formation in Arabidopsis thaliana by specifically interfering with male meiotic cytokinesis. Similar alterations in male meiotic cell division and gametophytic ploidy stability occur when gibberellic acid (GA) signaling is perturbed in developing anthers. In this study, we found that exogenous application of GA primarily induces second division restitution (SDR)-type pollen in Arabidopsis, similar to what cold does. Driven by the close similarity in cellular defects, we tested the hypothesis that cold-induced meiotic restitution is mediated by GA-DELLA signaling. Using a combination of chemical, genetic and cytological approaches, however, we found that both exogenously and endogenously altered GA signaling do not affect the cold sensitivity of male meiotic cytokinesis. Moreover, in vivo localization study using a GFP-tagged version of RGA protein revealed that cold does not affect the expression pattern and abundance of DELLA in Arabidopsis anthers at tetrad stage. Expression study found that transcript of RGA appears enhanced in cold-stressed young flower buds. Since our previous work demonstrated that loss of function of DELLA causes irregular male meiotic cytokinesis, we here conclude that cold-induced meiotic restitution is not mediated by DELLA-dependent GA signaling.

Elucidating the role of WRKY27 in male sterility in Arabidopsis

The WRKY proteins belong to a superfamily of TFs that play pivotal roles in responses to a wide range of biotic, abiotic, developmental and physiologic cues. Here, we assayed the accumulation of basal WRKY27 transcripts in diverse tissue including root, shoot, leaf and flowers. We demonstrated that plants over-expressing WRKY27 transcript levels exhibit growth aberrations and fertility defects. Scanning electron microscopic data suggest that WRKY27 overexpressor plants exhibit pollen dehiscence defects. Our fluorescein diacetate hydrolysis assay showed that flowers of plants overexpressing WRKY27 display significantly decreased pollen viability. These sterility-related phenotypes were not rescued by the exogenous applications of different phytohormones. Our results indicate the involvement of WRKY27 in particular for proper plant biomass accumulation and male fertility.

Chitosan nanoparticles as carrier systems for the plant growth hormone gibberellic acid

This work concerns the development of nanocarriers composed of alginate/chitosan (ALG/CS) and chitosan/tripolyphosphate (CS/TPP) for the plant growth regulator gibberellic acid (GA₃). ALG/CS nanoparticles with and without GA₃ presented mean size of 450±10nm, polydispersity index (PDI) of 0.3, zeta potential of -29±0.5mV, concentrations of 1.52×10¹¹ and 1.92×10¹¹ nanoparticles mL^-1, respectively, and 100% encapsulation efficiency. CS/TPP nanoparticles with and without GA₃ presented mean size of 195±1nm, PDI of 0.3, zeta potential of +27±3mV, concentrations of 1.92×10¹² and 3.54×10¹² nanoparticles mL^-1, respectively, and 90% encapsulation efficiency. The nanoparticles were stable during 60days and the two systems differed in terms of the release mechanism, with the release depending on factors such as pH and temperature. Bioactivity assays using Phaseolus vulgaris showed that the ALG/CS-GA₃ nanoparticles were most effective in increasing leaf area and the levels of chlorophylls and carotenoids. The systems developed showed good potential, providing greater stability and efficiency of this plant hormone in agricultural applications.

Bamboo Flowering from the Perspective of Comparative Genomics and Transcriptomics

Bamboos are an important member of the subfamily Bambusoideae, family Poaceae. The plant group exhibits wide variation with respect to the timing (1-120 years) and nature (sporadic vs. gregarious) of flowering among species. Usually flowering in woody bamboos is synchronous across culms growing over a large area, known as gregarious flowering. In many monocarpic bamboos this is followed by mass death and seed setting. While in sporadic flowering an isolated wild clump may flower, set little or no seed and remain alive. Such wide variation in flowering time and extent means that the plant group serves as repositories for genes and expression patterns that are unique to bamboo. Due to the dearth of available genomic and transcriptomic resources, limited studies have been undertaken to identify the potential molecular players in bamboo flowering. The public release of the first bamboo genome sequence Phyllostachys heterocycla, availability of related genomes Brachypodium distachyon and Oryza sativa provide us the opportunity to study this long-standing biological problem in a comparative and functional genomics framework. We identified bamboo genes homologous to those of Oryza and Brachypodium that are involved in established pathways such as vernalization, photoperiod, autonomous, and hormonal regulation of flowering. Additionally, we investigated triggers like stress (drought), physiological maturity and micro RNAs that may play crucial roles in flowering. We also analyzed available transcriptome datasets of different bamboo species to identify genes and their involvement in bamboo flowering. Finally, we summarize potential research hurdles that need to be addressed in future research.