Molecular basis of plant architecture

BR signalling haplotypes contribute to indica-japonica differentiation for grain yield and quality in rice

The functional difference of natural variations in conserved BR signalling genes and the genetic basis of rice indica-japonica differentiation are important yet unknown. Here, we discovered natural variations of the four key components (OsBRI1, OsBAK1, OsGSK3 and OsBZR1) in BR signalling pathway by GWAS using an indicator of indica-japonica differentiation in rice. Two major BR signalling haplotypes (BSHs), caused by co-selected variations of the four genetically unlinked genes, were identified to be highly differentiated between rice subspecies. The genetic contributions of BSHs to grain yield and quality were much higher than that of each component. Introducing alleles of japonica into indica employing substitution lines of OsBAK1, complementation lines of OsGSK3 and genetic populations of OsBRI1/OsBAK1/OsGSK3 confirmed their functional differences between two subspecies. The BSH differentiation led to weaker interaction between OsBRI1 and OsBAK1, stronger autophosphorylation and kinase activity of OsGSK3, less RNA/proteins and stronger phosphorylation of OsBZR1, and weaker BR sensitivity in indica than japonica rice, and regular expression trends of BR-response genes between subspecies, and then synergistically enhanced yield and superior quality of indica. Our results demonstrate that BSHs contribute to rice inter-subspecies diversity, and will provide proof-of-concept breeding strategy and useful targets in crops.

Root microbiota regulates tiller number in rice

Rice tillering is an important agronomic trait regulated by plant genetic and environmental factors. However, the role and mechanism of the root microbiota in modulating rice tillering have not been explored. Here, we examined the root microbiota composition and tiller numbers of 182 genome-sequenced rice varieties grown under field conditions and uncovered a significant correlation between root microbiota composition and rice tiller number. Using cultivated bacterial isolates, we demonstrated that various members of the root microbiota can regulate rice tillering in both laboratory and field conditions. Genetic, biochemical, and structural analyses revealed that cyclo(Leu-Pro), produced by the tiller-inhibiting bacterium Exiguobacterium R2567, activates the rice strigolactone (SL) signaling pathway by binding to the SL receptor OsD14, thus regulating tillering. The present work provides insight into how the root microbiota regulates key agronomic traits and offers a promising strategy for optimizing crop growth by harnessing the root microbiota in sustainable agriculture.

LTD1 plays a key role in rice tillering regulation through cooperation with CycH1;1 and TFB2 subunits of the TFIIH complex

Tillering contributes greatly to grain yield in rice (Oryza sativa). At present, many genes involved in rice tillering regulation have been cloned and characterized. However, the identification of more novel genes is still necessary to fully understand the molecular mechanisms regulating rice tillering. In this study, we isolated a low-tillering and dwarf 1 (ltd1) mutant in indica rice. Map-based cloning and MutMap analysis showed that the candidate gene LTD1 (LOC_Os01g19760) encodes a putative FAM91A1 protein with an unknown function in plants. LTD1-complementation and -RNAi confirmed that LTD1 is responsible for the mutant phenotype of ltd1. The LTD1 protein is localized to the plasma membrane, endoplasmic reticulum, and multi-vesicular bodies. Furthermore, protein interaction and colocalization assays showed that LTD1 interacts with both the TFB2 subunit of the core subcomplex and the CycH1;1 subunit of the cyclin-dependent kinase-activating kinase (CAK) subcomplex of the TFIIH complex, and TFB2 also interacts with CycH1;1. qRT-PCR demonstrated that the expression levels of most genes related to the cell cycle are changed significantly in the ltd1 tiller buds, and flow cytometry assays revealed that there are more polyploid nuclei in the ltd1 leaves and roots, suggesting that LTD1 could be involved in cell cycle regulation. Taken together, our findings indicated that LTD1 plays a key role in rice tillering regulation by involvement in the cell cycle through cooperation with CycH1;1 and TFB2 subunits of TFIIH. This work also sheds light on the biological function of FAM91A1 in regulating important agronomic traits of rice.

Identification of a novel dwarfing gene, Rht_m097, on chromosome 4BS in common wheat

Plant height is a crucial agronomic trait in wheat, regulated by multiple genes, and significantly influences plant architecture and wheat yield. In this study, a novel dwarf mutant, designated as m097, was developed and characterized through the treatment of seeds from the common wheat cultivar Jinmai47 with ethyl methanesulfonate (EMS). Microscopic analysis revealed that the dwarf phenotype was attributed to a reduction in the longitudinal cell size of the stem. Similar to the wild type, m097 exhibited sensitivity to exogenous gibberellic acid (GA). Genetic analysis indicated that the reduced plant height in m097 was regulated by a semi-dominant dwarfing gene, Rht_m097. Through bulk segregant analysis (BSA) utilizing the wheat 660K SNP array, Rht_m097 was mapped and confined to a region of approximately 2.58 Mb on chromosome arm 4BS, encompassing 16 high-confidence annotated genes. In addition, transcriptome sequencing (RNA-seq) was conducted on the first internode below the panicle of JM47 and m097 at the jointing stage, leading to the identification of two potential candidate genes exhibiting differential expression. Furthermore, the analysis of gene ontology and metabolic pathways from RNA-seq data indicated that the down-regulated differentially expressed genes (DEGs) in m097 were biologically classified as regulating actin cortical patch organization and assembly. Concurrently, it was observed that the up-regulated DEGs were significantly enriched in various phytohormone metabolic pathways, including those involved in indole-3-acetic acid (IAA) biosynthesis, jasmonic acid biosynthesis, and gibberellin signaling. Overall, this study provides a novel genetic resource for the breeding of dwarf wheat and establishes a foundation for subsequent gene cloning.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-025-01558-0.

FZP modulates tillering via OsMADS57 in rice

The number of tillers in rice directly determines the number of panicles, which is crucial for enhancing plant architecture and achieving high yields. Some important genes regulating rice tillering have been identified, but their underlying mechanisms remain unclear. FRIZZY PANICLE (FZP) encodes an AP2/ERF transcription factor. Beyond its well-established role in promoting spikelet formation during the reproductive phase, here we demonstrate that FZP also inhibits axillary buds outgrowth in the vegetative phase by suppressing the expression of a MADS-box gene (OsMADS57) that functions as a growth promoter. Consequently, genome editing of the FZP-bound cis-motif in the promoter of OsMADS57 releases its expression, leading to more tillers. Furthermore, domestication analysis shows that FZP has undergone strong selection in cultivated rice, while the downstream gene OsMADS57 has been differentiated between indica and japonica subspecies. Four functional SNPs in the promoter of OsMADS57 can increase rice tillering in most indica accessions by enhancing its expression. Our findings expose hidden pleiotropy of classic spikelet identity genes that are redeployed to control stem form, potentially enriching the gene resources for rice genetic improvement.

Genome-Wide Mapping, Allelic Fingerprinting, and Haplotypes Validation Provide Insights Into the Genetic Control of Phenotypic Plasticity in Rice

Plant density significantly impacts photosynthesis, crop growth, and yield, thereby shaping the [CO2] fertilization effect and intricate physiological interactions in rice. An association panel of 171 rice genotypes was evaluated for physiological and yield-related traits, including the cumulative response index, under both normal planting density (NPD) and low planting density (LPD) conditions. LPD, serving as a proxy for elevated atmospheric [CO2], significantly increased all trait values, except for harvest index, compared to NPD. A genome-wide association study identified 172 QTNs, including 12 associated with multiple traits under NPD or LPD conditions. Candidate gene mining and network analysis within QTN regions identified potential candidates such as OsHAK1, RGA1, OsalphaCA3, OsalphaCA4, OsalphaCA5, OsCYP38, and OsPIN1, influencing various physiological and yield-related traits under LPD conditions. A significant relationship between the percentage of favorable alleles in genotypes and their performance under different conditions was observed. Potential haplotypes were validated using genotypes identified with contrasting [CO2] responses, grown under LPD and Free-Air [CO2] Enrichment facility. These findings can aid in selectively breeding genotypes with favorable alleles or haplotypes to enhance [CO2] responsiveness in rice. Incorporating greater phenotypic plasticity can help develop climate-smart rice varieties that increase grain yield and quality while mitigating losses from warming temperatures.

The OsMAPK6-OsWRKY72 module positively regulates rice leaf angle through brassinosteroid signals

Leaf angle is a major agronomic trait that determines plant architecture, which directly affects rice planting density, photosynthetic efficiency, and yield. The plant phytohormones brassinosteroids (BRs) and the MAPK signaling cascade are known to play crucial roles in regulating leaf angle, but the underlying molecular mechanisms are not fully understood. Here, we report a rice WRKY family transcription factor gene, OsWRKY72, which positively regulates leaf angle by affecting lamina joint development and BR signaling. Phenotypic analysis showed that oswrky72 mutants have smaller leaf angles and exhibit insensitivity to exogenous BRs, whereas OsWRKY72 overexpression lines show enlarged leaf angles and are hypersensitive to exogenous BRs. Histological sections revealed that the change in leaf inclination is due to asymmetric cell proliferation and growth at the lamina joint. Further investigation showed that OsWRKY72 binds directly to the promoter region of BR receptor kinase (OsBRI1), a key gene in the BR signaling pathway, and activates its expression to positively regulate rice BR signaling. In addition, we discovered that OsWRKY72 interacts with and is phosphorylated by OsMAPK6, and this phosphorylation event can enhance OsWRKY72 activity in promoting OsBRI1 expression. Genetic evidence confirmed that OsMAPK6, OsWRKY72, and OsBRI1 function in a common pathway to regulate leaf angle. Collectively, our findings clarify the critical role of the OsWRKY72 transcription factor in regulating rice leaf angle. These results provide valuable insights into the molecular regulatory networks that govern plant architecture in rice.

Dwarfs standing tall: breeding towards the 'Yellow revolution' through insights into plant height regulation

High oilseed production is an exigency due to the increasing edible oil consumption of the growing population. Rapeseed and mustard are cultivated worldwide and contribute significantly to the world's total oilseed production. Already a plateau is reached in terms of area and yield in most of the existing cultivars. Most of the commercially cultivated high yielding rapeseed and mustard varieties are tall, mainly due to a wider use of heterosis. However, they are susceptible to lodging and consequent yield losses. Plant yield is strongly dependent upon its architecture; therefore, 'ideotype breeding' is the key approach adopted to develop new varieties with enhanced yield potential, which is less explored in these crops. Dwarf/ semi dwarf plant type varieties has shown its improved yield potential over tall plant type in cereals which further leads to 'Green revolution' in Asian countries. Although, many induced dwarf mutants in rapeseed and mustard were isolated, unlike dwarf green-revolution varieties of cereals, most of them had undesirable plant types with defects including extreme dwarfism and sterility, leading to poor yield potential. Understanding the genetic and molecular mechanisms governing plant height and its correlation with yield and yield contributing characters is crucial. In this review, recent insights into genetic, molecular, and anatomical regulation of plant height have been discussed. The role of hormones, their crosstalk, and hormonal control for cell division and expansion have been delineated with respect to plant architecture. Many dwarfing genes are identified as being part of various phytohormone pathways. Parallelly, molecular links between plant height and flowering time have been explored. The overall synthesis of the review points out some key target pathways and genes that will be useful for plant breeders as well as biotechnologists for targeted genome editing for improving plant architecture without a yield penalty.

Genetic dissection of internode length confers improvement for ideal plant architecture in maize

The optimal plant architecture, characterized by short stature, helps mitigate lodging, enables high-density planting, and facilitates mechanized harvesting. Internode length (IL), a crucial component of plant height in maize, plays a significant role in these processes. However, the genetic mechanisms underlying internode elongation remain poorly understood. In this study, we conducted a genome-wide association study to dissect the genetic architecture of IL in maize. The lengths of five internodes above and below the ear (referred as IL-related traits) were collected across multiple environments, revealing substantial variation. A total of 108 quantitative trait loci (QTL) were associated with 11 IL-related traits, with 17 QTL co-detected by different traits. Notably, three QTL have been selected in maize breeding progress. Three hundred and three genes associated with IL were found to operate through plant hormone signal transduction, receptor activity, and carbon metabolism pathways, influencing internode elongation. ZmIL1, which encodes alcohol dehydrogenase, exhibited a high expression level in internodes during the vegetative stage and has been selected in Chinese modern maize breeding. Additionally, ZmIL2 and ZmIL3 emerged as other crucial regulators of IL. Importantly, ZmIL1 has potential applications in maize varieties in the Huang-Huai-Hai region. This study represents the first comprehensive report on the genetic architecture of nearly all ILs in maize, providing profound insights into internode elongation mechanisms and genetic resources. These findings hold significant implications for dwarf breeding programs aimed at optimizing plant architecture for enhancing agronomic performance.

CsIREH1 phosphorylation regulates DELLA protein affecting plant height in cucumber (Cucumis sativus)

Plant height is a critical agronomic trait that affects crop yield, plant architecture, and environmental adaptability. Gibberellins (GAs) regulate plant height, with DELLA proteins acting as key repressors in the GA signaling pathway by inhibiting GA-induced growth. While DELLA phosphorylation is essential for regulating plant height, the precise mechanisms underlying this process remain incompletely understood. In this study, we identified a cucumber mutant with delayed growth, which exhibited reduced sensitivity to GA treatment. Through bulked segregant analysis (BSA-seq) combined with molecular marker linkage analysis, we successfully identified and cloned the gene responsible for the dwarf phenotype, CsIREH1 (INCOMPLETE ROOT HAIR ELONGATION 1), which encodes an AGC protein kinase. Further research revealed that CsIREH1 interacts with and phosphorylates DELLA proteins, specifically targeting CsGAIP and CsGAI2. We propose that IREH1-dependent phosphorylation of DELLA proteins prevents their excessive accumulation, thereby maintaining normal plant growth. Therefore, investigating the role of IREH1-mediated DELLA phosphorylation provides valuable insights and theoretical foundations for understanding how plants regulate growth mechanisms.

First note of QTL mapping of low vigor traits using the updated F2 'Koroneiki' linkage map of olive

The olive tree (Olea europaea L.), which characterizes the agriculture of the Mediterranean basin, faces challenges adapting to high-density orchards and mechanized cultivation. This study addresses a key issue: controlling tree size to enhance efficiency and manageability in olive cultivation. Utilizing genetic mapping methods, we have identified significant Quantitative Trait Loci (QTL) and candidate genes associated with low-vigor traits in olive trees. Our research on the 'Koroneiki' F2 progeny, which exhibits low vigor traits but remains underutilized in breeding programs, has pinpointed a QTL linked to trunk basal diameter-a trait correlated with plant height based on morphological measurements. Results underscore a strong genetic control of these traits, with a consistent correlation observed over time. We identified two candidate genes - Acid Phosphatase 1, Shikimate O-hydroxycinnamoyltransferase, and a SNP Marker likely associated with Calcium Responsive Proteins - each potentially interacting with plant hormones to influence growth. Controlling olive tree size presents several challenges, including the genetic complexity of polygenic traits like size and vigor, and limited rootstock options. By integrating reference genomes with our genetic analysis, we offer a conceptual advancement that could substantially accelerate breeding timelines compared to traditional approaches. Although genome editing is still a future possibility due to the complexity of olive genetics and the species' recalcitrance to transformation, our study lays a foundational understanding to guide future breeding programs. By targeting the identified candidate genes, this research represents a pivotal step toward selecting new low-vigor genotypes and rootstocks, contributing to innovations in olive cultivation.

Performing whole-genome association analysis of winter wheat plant height using the 55K chip

Plant height is a critical agronomic that affects both plant architecture and yield. To decipher the genetic mechanisms underlying winter wheat plant height and identify candidate genes associated with this trait, we conducted phenotypic analysis on 239 wheat varieties (lines) collected from around the world. This analysis was complemented by genotyping using the wheat 55K SNP chip. A Wholegenome association analysis (GWAS) of wheat plant height was conducted utilizing the MLM (Q+K) model within TASSLE software. The results revealed significant phenotypic variation in wheat plant height across different years, with coefficients of variation ranging from 0.96% to 1.97%. Additionally, there was a strong correlation in plant height measurements between different years. GWAS identified 44 SNP markers significantly associated with wheat plant height across various environments (P ≤ 0.00001), predominantly distributed on chromosomes 1B, 1D, 2A, 2B, 2D, 3B, 3D, 4A, 4B, 6B, 6D, and 7D, explaining individual phenotypic variance rates ranging from 5.00% to 11.11%. Further, by mining association loci with substantial phenotypic effects and stability across multiple environments, seven candidate genes related to wheat plant height have been identified. This study provides new genetic markers and resources for improving wheat plant height.

Genome-wide association analysis reveals novel candidate loci and a gene regulating tiller number in orchardgrass

Tillers are specialized lateral shoots arising from axillary buds at basal nodes, and are also an important agronomic trait that determines the aboveground biomass and grain yield of various gramineous crops. So far, few genes have been reported to control tiller formation and most have been in the annual crop rice (Oryza sativa). Orchardgrass (Dactylis glomerata) is an important perennial forage crop with great economic and ecological value, but its genes regulating tillering have remained largely unknown. In the present study, we used a natural population of 264 global orchardgrass germplasms to determine genes associated with quantitative variation in tiller number through genome-wide association study analysis. A total of 19 putative loci and 55 genes associated with tiller number were thus identified. Additionally, 26 putative differentially expressed genes with tiller number, including DgCYC-C1, were identified by RNA-seq and genome-wide association study analysis. DgCYC-C1 which is involved in cell division, was overexpressed, revealing that DgCYC-C1 positively regulates tiller number. These results provide some new candidate genes or loci for the improvement of tiller number in crops, which might advance new sustainable strategies to meet global crop production challenges.

Characterization of the gibberellic oxidase gene SdGA20ox1 in Sophora davidii (Franch.) skeels and interaction protein screening

Gibberellin 20-oxidases (GA20oxs) are multifunctional enzymes involved in regulating gibberellin (GA) biosynthesis and controlling plant growth. We identified and characterized the GA20ox1 gene in a plant height mutant of Sophora davidii, referred to as SdGA20ox1. This gene was expressed in root, stem, and leaf tissues of the adult S. davidii plant height mutant, with the highest expression observed in the stem. The expression of SdGA20ox1 was regulated by various exogenous hormones. Overexpression of SdGA20ox1 in Arabidopsis resulted in significant elongation of hypocotyl and root length in seedlings, earlier flowering, smaller leaves, reduced leaf chlorophyll content, lighter leaf color, a significant increase in adult plant height, and other phenotypes. Additionally, transgenic plants exhibited a substantial increase in biologically active endogenous GAs (GA1, GA3, and GA4) content, indicating that overexpression of SdGA20ox1 accelerates plant growth and development. Using a yeast two-hybrid (Y2H) screen, we identified two SdGA20ox1-interacting proteins: the ethylene receptor EIN4 (11430582) and the rbcS (11416005) protein. These interactions suggest a potential regulatory mechanism for S. davidii growth. Our findings provide new insights into the role of SdGA20ox1 and its interacting proteins in regulating the growth and development of S. davidii.

A systematic regulatory network related to bulbil formation in Lilium lancifolium based on metabolome and transcriptome analyses

BACKGROUND

Lilium lancifolium is a special wild triploid species native to China and can produce abundant bulbils on its stem under natural conditions, which is very valuable to study bulbil organogenesis in plants. Although similar to the lateral and tillering principles, the molecular mechanism underlying bulbil formation has remained incompletely understood.

RESULTS

The metabolome and transcriptome of L. lancifolium bulbils across four development stages were analyzed. The pairwise comparison of metabolomes across the four stages identified 17 differential hormones, predominantly auxin (IAA), cytokinin (CK), and jasmonic acid (JA). Short Time-series Expression Miner (STEM) trend analysis of differential genes revealed four significant trends across these stages. The KEGG enrichment analysis of the four clusters highlighted pathways, such as plant hormone signal transduction, which were speculated to play a crucial role in development stages. these pathways were speculated to play a crucial role in development stages. To explore the key differential expressed genes and transcription factors associated with bulbil occurrence, two periods were focused on: Ll_UN and Ll_DN, which represented the stages with and without bulbils, respectively. Through correlation analysis and qRT-PCR analysis, 11 candidate differentially expressed genes and 27 candidate transcription factors were selected. By spraying exogenous hormones to validate these candidates, LlbHLH128, LlTIFY10A, LlbHLH93, and LlMYB108, were identified as the key genes for L. lancifolium bulbils.

CONCLUSION

A regulatory network of L. lancifolium bulbil development was predicted. LlTIFY10A and LlbHLH93 might be involved in the JA and auxin signal transduction pathways, which jointly formed a regulatory network to affect the occurrence of L. lancifolium bulbil. This study not only provided more information about the differentially expressed genes and metabolites through transcriptome and metabolomics analyses, but also provided a clearer understanding of the effect of hormones on bulbil formation in lily.

LAZY4 acts additively with the starch-statolith-dependent gravity-sensing pathway to regulate shoot gravitropism and tiller angle in rice

Rice tiller angle is a key agronomic trait that has significant effects on the establishment of a high-yield rice population. However, the molecular mechanism underlying the control of rice tiller angle remains to be clarified. Here, we characterized the novel tiller-angle gene LAZY4 (LA4) in rice through map-based cloning. LA4 encodes a C3H2C3-type RING zinc-finger E3 ligase localized in the nucleus, and an in vitro ubiquitination assay revealed that the conserved RING finger domain is essential for its E3 ligase activity. We found that expression of LA4 can be induced by gravistimulation and that loss of LA4 function leads to defective shoot gravitropism caused by impaired asymmetric auxin redistribution upon gravistimulation. Genetic analysis demonstrated that LA4 acts in a distinct pathway from the starch biosynthesis regulators LA2 and LA3, which function in the starch-statolith-dependent pathway. Further genetic analysis showed that LA4 regulates shoot gravitropism and tiller angle by acting upstream of LA1 to mediate lateral auxin transport upon gravistimulation. Our studies reveal that LA4 regulates shoot gravitropism and tiller angle upstream of LA1 through a novel pathway independent of the LA2-LA3-mediated gravity-sensing mechanism, providing new insights into the rice tiller-angle regulatory network.

LATA1, a RING E3 ligase, modulates the tiller angle by affecting auxin asymmetric distribution and content in rice

The tiller angle is an important agronomic trait that determines plant architecture and grain yield in rice (Oryza sativa L.). However, the molecular regulation mechanism of the rice tiller angle remains unclear. Here, we identified a rice tiller angle gene, LARGE TILLER ANGLE 1 (LATA1), using the MutMap approach. LATA1 encodes a C3H2C3-type RING zinc finger E3 ligase and the conserved region of the RING zinc finger is essential for its E3 activity. LATA1 was highly expressed in the root and tiller base and LATA1-GFP fusion protein was specifically localized to the nucleus. The mutation of LATA1 significantly reduced indole-3-acetic acid content and attenuated lateral auxin transport, thereby resulting in defective shoot gravitropism and spreading plant architecture in rice. Further investigations found that LATA1 may indirectly affect gravity perception by modulating the sedimentation rate of gravity-sensing amyloplasts upon gravistimulation. Our findings provide new insights into the molecular mechanism underlying the rice tiller angle and new genetic resource for the improvement of plant architecture in rice.

The SINA1-BSD1 Module Regulates Vegetative Growth Involving Gibberellin Biosynthesis in Tomato

In plants, vegetative growth is controlled by synergistic and/or antagonistic effects of many regulatory factors. Here, the authors demonstrate that the ubiquitin ligase seven in absentia1 (SINA1) mammalian BTF2-like transcription factors, Drosophila synapse-associated proteins, and yeast DOS2-like proteins (BSD1) function as a regulatory module to control vegetative growth in tomato via regulation of the production of plant growth hormone gibberellin (GA). SINA1 negatively regulates the protein level of BSD1 through ubiquitin-proteasome-mediated degradation, and the transgenic tomato over-expressing SINA1 (SINA1-OX) resembles the dwarfism phenotype of the BSD1-knockout (BSD1-KO) tomato plant. BSD1 directly activates expression of the BSD1-regulated gene 1 (BRG1) via binding to a novel core BBS (standing for BSD1 binding site) binding motif in the BRG1 promoter. Knockout of BRG1 (BRG1-KO) in tomato also results in a dwarfism phenotype, suggesting BRG1 plays a positive role in vegetative growth as BSD1 does. Significantly, GA contents are attenuated in transgenic SINA1-OX, BSD1-KO, and BRG1-KO plants exhibiting dwarfism phenotype and exogenous application of bioactive GA3 restores their vegetative growth. Moreover, BRG1 is required for the expression of multiple GA biosynthesis genes and BSD1 activates three GA biosynthesis genes promoting GA production. Thus, this study suggests that the SINA1-BSD1 module controls vegetative growth via direct and indirect regulation of GA biosynthesis in tomato.

DWARF AND LESS TILLERS ON CHROMOSOME 3 promotes tillering in rice by sustaining FLORAL ORGAN NUMBER 1 expression

Three key factors determine yield in rice (Oryza sativa): panicle number, grain number, and grain weight. Panicle number is strongly associated with tiller number. Although many genes regulating tillering have been identified, whether Dof proteins are involved in controlling plant architecture remains unknown. The dwarf and less tillers on chromosome 3 (dlt3) rice mutant produces fewer tillers than the wild type. We cloned DLT3, which encodes a Dof protein that interacts with MONOCULM 3 (MOC3) in vivo and in vitro and recruits MOC1, forming a DLT3-MOC3-MOC1 complex. DLT3 binds to the promoter of FLORAL ORGAN NUMBER 1 (FON1) to activate its transcription and positively regulate tiller number. The overexpression of MOC1, MOC3, or FON1 in the dlt3 mutant increased tiller number. Collectively, these results suggest a model in which DLT3 regulates tiller number by maintaining the expression of MOC1, MOC3, and FON1. We discovered that DLT3 underwent directional selection in the Xian/indica and Geng/japonica populations during rice domestication. To provide genetic resources for breeding varieties with optimal panicle numbers, we performed large-scale diversity sequencing of the 1,080-bp DLT3 coding region of 531 accessions from different countries and regions. Haplotype analysis showed that the superior haplotype, DLT3H1, produced the most tillers, while haplotype DLT3H6 produced the fewest tillers. Our study provides important germplasm resources for breeding super high-yielding rice varieties with combinations of superior haplotypes in different target genes, which will help overcome the challenge of food and nutritional security in the future.

A dynamic regulome of shoot-apical-meristem-related homeobox transcription factors modulates plant architecture in maize

BACKGROUND

The shoot apical meristem (SAM), from which all above-ground tissues of plants are derived, is critical to plant morphology and development. In maize (Zea mays), loss-of-function mutant studies have identified several SAM-related genes, most encoding homeobox transcription factors (TFs), located upstream of hierarchical networks of hundreds of genes.

RESULTS

Here, we collect 46 transcriptome and 16 translatome datasets across 62 different tissues or stages from the maize inbred line B73. We construct a dynamic regulome for 27 members of three SAM-related homeobox subfamilies (KNOX, WOX, and ZF-HD) through machine-learning models for the detection of TF targets across different tissues and stages by combining tsCUT&Tag, ATAC-seq, and expression profiling. This dynamic regulome demonstrates the distinct binding specificity and co-factors for these homeobox subfamilies, indicative of functional divergence between and within them. Furthermore, we assemble a SAM dynamic regulome, illustrating potential functional mechanisms associated with plant architecture. Lastly, we generate a wox13a mutant that provides evidence that WOX13A directly regulates Gn1 expression to modulate plant height, validating the regulome of SAM-related homeobox genes.

CONCLUSIONS

The SAM-related homeobox transcription-factor regulome presents an unprecedented opportunity to dissect the molecular mechanisms governing SAM maintenance and development, thereby advancing our understanding of maize growth and shoot architecture.

BTA2 regulates tiller angle and the shoot gravity response through controlling auxin content and distribution in rice

Tiller angle is a key agricultural trait that establishes plant architecture, which in turn strongly affects grain yield by influencing planting density in rice. The shoot gravity response plays a crucial role in the regulation of tiller angle in rice, but the underlying molecular mechanism is largely unknown. Here, we report the identification of the BIG TILLER ANGLE2 (BTA2), which regulates tiller angle by controlling the shoot gravity response in rice. Loss-of-function mutation of BTA2 dramatically reduced auxin content and affected auxin distribution in rice shoot base, leading to impaired gravitropism and therefore a big tiller angle. BTA2 interacted with AUXIN RESPONSE FACTOR7 (ARF7) to modulate rice tiller angle through the gravity signaling pathway. The BTA2 protein was highly conserved during evolution. Sequence variation in the BTA2 promoter of indica cultivars harboring a less expressed BTA2 allele caused lower BTA2 expression in shoot base and thus wide tiller angle during rice domestication. Overexpression of BTA2 significantly increased grain yield in the elite rice cultivar Huanghuazhan under appropriate dense planting conditions. Our findings thus uncovered the BTA2-ARF7 module that regulates tiller angle by mediating the shoot gravity response. Our work offers a target for genetic manipulation of plant architecture and valuable information for crop improvement by producing the ideal plant type.

OsMED14_2, a tail module subunit of Mediator complex, controls rice development and involves jasmonic acid

The Mediator complex is essential for eukaryotic transcription, yet its role and the function of its individual subunits in plants, especially in rice, remain poorly understood. Here, we investigate the function of OsMED14_2, a subunit of the Mediator tail module, in rice development. Overexpression and knockout of OsMED14_2 resulted in notable changes in panicle morphology and grain size. Microscopic analysis revealed impact of overexpression on pollen maturation, reflected by reduced viability, irregular shapes, and aberrant intine development. OsMED14_2 was found to interact with proteins involved in pollen development, namely, OsMADS62, OsMADS63 and OsMADS68, and its overexpression negatively affected the expression of OsMADS68 and the expression of other genes involved in intine development, including OsCAP1, OsGCD1, OsRIP1, and OsCPK29. Additionally, we found that OsMED14_2 overexpression influences jasmonic acid (JA) homeostasis, affecting bioactive JA levels, and expression of OsJAZ genes. Our data suggest OsMED14_2 may act as a regulator of JA-responsive genes through its interactions with OsHDAC6 and OsJAZ repressors. These findings contribute to better understanding of the Mediator complex's role in plant traits regulation.

Analysis on morphological characteristics and identification of candidate genes during the flowering development of alfalfa

Flower development is a crucial and complex process in the reproductive stage of plants, which involves the interaction of multiple endogenous signals and environmental factors. However, regulatory mechanism of flower development was unknown in alfalfa (Medicago sativa). In this study, the three stages of flower development of 'M. sativa cv. Gannong No. 5' (G5) and its early flowering and multi flowering mutant (MG5) were comparatively analyzed by transcriptomics. The results showed that compared with late bud stage (S1), 14287 and 8351 differentially expressed genes (DEGs) were identified at early flower stage (S2) in G5 and MG5, and 19941 and 19469 DEGs were identified at late flower stage (S3). Compared with S2, 9574 and 10870 DEGs were identified at S3 in G5 and MG5, respectively. Venn analysis revealed that 547 DEGs were identified among the three comparison groups. KEGG pathway enrichment analysis showed that these genes were involved in the development of alfalfa flowers through redox pathways and plant hormone signaling pathways. Key candidate genes including SnRK2, BSK, GID1, DELLA and CRE1, for regulating the development from buds to mature flowers in alfalfa were screened. In addition, differential expression of transcription factors such as MYB, AP2, bHLH, C2C2, MADS-box, NAC, bZIP, B3 and AUX/IAA also played an important role in this process. The results laid a theoretical foundation for studying the molecular mechanisms of the development process from buds to mature flowers in alfalfa.

Morphological, anatomical, and transcriptomics analysis reveals the regulatory mechanisms of cassava plant height development

BACKGROUND

Cassava is one of three major potato crops and the sixth most important food crop globally. Improving yield remains a primary aim in cassava breeding. Notably, plant height significantly impacts the yield and quality of crops; however, the mechanisms underlying cassava plant height development are yet to be elucidated.

RESULTS

In this study, we investigated the mechanisms responsible for cassava plant height development using phenotypic, anatomical, and transcriptomic analyses. Phenotypic and anatomical analysis revealed that compared to the high-stem cassava cultivar, the dwarf-stem cassava cultivar exhibited a significant reduction in plant height and a notable increase in internode tissue xylem area. Meanwhile, physiological analysis demonstrated that the lignin content of dwarf cassava was significantly higher than that of high cassava. Notably, transcriptome analysis of internode tissues identified several differentially expressed genes involved in cell wall synthesis and expansion, plant hormone signal transduction, phenylpropanoid biosynthesis, and flavonoid biosynthesis between the two cassava cultivars.

CONCLUSIONS

Our findings suggest that internode tissue cell division, secondary wall lignification, and hormone-related gene expression play important roles in cassava plant height development. Ultimately, this study provides new insights into the mechanisms of plant height morphogenesis in cassava and identifies candidate regulatory genes associated with plant height that can serve as valuable genetic resources for future crop dwarfing breeding.

Plant regeneration in the new era: from molecular mechanisms to biotechnology applications

Plants or tissues can be regenerated through various pathways. Like animal regeneration, cell totipotency and pluripotency are the molecular basis of plant regeneration. Detailed systematic studies on Arabidopsis thaliana gradually unravel the fundamental mechanisms and principles underlying plant regeneration. Specifically, plant hormones, cell division, epigenetic remodeling, and transcription factors play crucial roles in reprogramming somatic cells and reestablishing meristematic cells. Recent research on basal non-vascular plants and monocot crops has revealed that plant regeneration differs among species, with various plant species using distinct mechanisms and displaying significant differences in regenerative capacity. Conducting multi-omics studies at the single-cell level, tracking plant regeneration processes in real-time, and deciphering the natural variation in regenerative capacity will ultimately help understand the essence of plant regeneration, improve crop regeneration efficiency, and contribute to future crop design.

An insight into the roles of ubiquitin-specific proteases in plants: development and growth, morphogenesis, and stress response

Ubiquitination is a highly conserved and dynamic post-translational modification in which protein substrates are modified by ubiquitin to influence their activity, localization, or stability. Deubiquitination enzymes (DUBs) counter ubiquitin signaling by removing ubiquitin from the substrates. Ubiquitin-specific proteases (UBPs), the largest subfamily of DUBs, are conserved in plants, serving diverse functions across various cellular processes, although members within the same group often exhibit functional redundancy. Here, we briefly review recent advances in understanding the biological roles of UBPs, particularly the molecular mechanism by which UBPs regulate plant development and growth, morphogenesis, and stress response, which sheds light on the mechanistic roles of deubiquitination in plants.

PdRabG3f interfered with gibberellin-mediated internode elongation and xylem developing in poplar

As a member of the small GTPases family, Rab GTPases play a key role in specifying transport pathways in the intracellular membrane trafficking system and are involved in plant growth and development. By quantitative trait locus (QTL) mapping, PdRabG3f was identified as a candidate gene associated with shoot height in a hybrid offspring of Populus deltoides 'Danhong' × Populus simonii 'Tongliao1'. PdRabG3f localized to the nucleus, endoplasmic reticulum and tonoplast and was primarily expressed in the xylem and cambium. Overexpression of PdRabG3f in Populus alba × Populus glandulosa (84 K poplar) had inhibitory effects on vertical and radical growth. In the transgenic lines, there were evident changes in the levels of 15 gibberellin (GA) derivatives, and the application of exogenous GA3 partially restored the phenotypes mediated by GAs deficiency. The interaction between PdRabG3f and RIC4, which was the GA-responsive factor, provided additional explanation for PdRabG3f's inhibitory effect on poplar growth. RNA-seq analysis revealed differentially expressed genes (DEGs) associated with cell wall, xylem, and gibberellin response. PdRabG3f interfering endogenous GAs levels in poplar might involve the participation of MYBs and ultimately affected internode elongation and xylem development. This study provides a potential mechanism for gibberellin-mediated regulation of plant growth through Rab GTPases.

Transcriptional Regulation and Gene Mapping of Internode Elongation and Late Budding in the Chinese Cabbage Mutant lcc

Two important traits of Chinese cabbage, internode length and budding time, destroy the maintenance of rosette leaves in the vegetative growth stage and affect flowering in the reproductive growth stage. Internodes have received much attention and research in rice due to their effect on lodging resistance, but they are rarely studied in Chinese cabbage. In Chinese cabbage, internode elongation affects not only the maintenance of rosette leaves but also bolting and yield. Budding is also an important characteristic of Chinese cabbage entering reproductive growth. Although many studies have reported on flowering and bolting, studies on bud emergence and the timing of budding are scarce. In this study, the mutant lcc induced by EMS (Ethyl Methane Sulfonate) was used to study internode elongation in the seedling stage and late budding in the budding stage. By comparing the gene expression patterns of mutant lcc and wild-type A03, 2280 differentially expressed genes were identified in the seedling stage, 714 differentially expressed genes were identified in the early budding stage, and 1052 differentially expressed genes were identified in the budding stage. Here, the transcript expression patterns of genes in the plant hormone signaling and clock rhythm pathways were investigated in relation to the regulation of internode elongation and budding in Chinese cabbage. In addition, an F2 population was constructed with the mutants lcc and R500. A high-density genetic map with 1602 marker loci was created, and QTLs for internode length and budding time were identified. Specifically, five QTLs for internode length and five QTLs for budding time were obtained. According to transcriptome data analysis, the internode length candidate gene BraA02g005840.3C (PIN8) and budding time candidate genes BraA02g003870.3C (HY5-1) and BraA02g005190.3C (CHS-1) were identified. These findings provide insight into the regulation of internode length and budding time in Chinese cabbage.

Multitrait engineering of Hassawi red rice for sustainable cultivation

Sustainable agriculture requires locally adapted varieties that produce nutritious food with limited agricultural inputs. Genome engineering represents a viable approach to develop cultivars that fulfill these criteria. For example, the red Hassawi rice, a native landrace of Saudi Arabia, tolerates local drought and high-salinity conditions and produces grain with diverse health-promoting phytochemicals. However, Hassawi has a long growth cycle, high cultivation costs, low productivity, and susceptibility to lodging. Here, to improve these undesirable traits via genome editing, we established efficient regeneration and Agrobacterium-mediated transformation protocols for Hassawi. In addition, we generated the first high-quality reference genome and targeted the key flowering repressor gene, Hd4, thus shortening the plant's lifecycle and height. Using CRISPR/Cas9 multiplexing, we simultaneously disrupted negative regulators of flowering time (Hd2, Hd4, and Hd5), grain size (GS3), grain number (GN1a), and plant height (Sd1). The resulting homozygous mutant lines flowered extremely early (∼56 days) and had shorter stems (approximately 107 cm), longer grains (by 5.1%), and more grains per plant (by 50.2%), thereby enhancing overall productivity. Furthermore, the awns of grains were 86.4% shorter compared to unedited plants. Moreover, the modified rice grain displayed improved nutritional attributes. As a result, the modified Hassawi rice combines several desirable traits that can incentivize large-scale cultivation and reduce malnutrition.

Unraveling the molecular mechanisms governing axillary meristem initiation in plants

MAIN CONCLUSION

Axillary meristems (AMs) located in the leaf axils determine the number of shoots or tillers eventually formed, thus contributing significantly to the plant architecture and crop yields. The study of AM initiation is unavoidable and beneficial for crop productivity. Shoot branching is an undoubted determinant of plant architecture and thus greatly impacts crop yield due to the panicle-bearing traits of tillers. The emergence of the AM is essential for the incipient bud formation, and then the bud is dormant or outgrowth immediately to form a branch or tiller. While numerous reviews have focused on plant branching and tillering development networks, fewer specifically address AM initiation and its regulatory mechanisms. This review synthesizes the significant advancements in the genetic and hormonal factors governing AM initiation, with a primary focus on studies conducted in Arabidopsis (Arabidopsis thaliana L.) and rice (Oryza sativa L.). In particular, by elaborating on critical genes like LATERAL SUPPRESSOR (LAS), which specifically regulates AM initiation and the networks in which they are involved, we attempt to unify the cascades through which they are positioned. We concentrate on clarifying the precise mutual regulation between shoot apical meristem (SAM) and AM-related factors. Additionally, we examine challenges in elucidating AM formation mechanisms alongside opportunities provided by emerging omics approaches to identify AM-specific genes. By expanding our comprehension of the genetic and hormonal regulation of AM development, we can develop strategies to optimize crop production and address global food challenges effectively.

The Function of SD1 on Shoot Length and its Pyramiding Effect on Shoot Length and Plant Height in Rice (Oryza sativa L.)

Strong seedling vigor is imperative to achieve stable seedling establishment and enhance the competitiveness against weeds in rice direct seeding. Shoot length (SL) is one of the important traits associated with seedling vigor in rice, but few genes for SL have been cloned so far. In the previous study, we identified two tightly linked and stably expressed QTLs for SL, qSL-1f and qSL-1d by genome-wide association study, and cloned the causal gene (LOC_Os01g68500) underlying qSL-1f. In the present study, we identify LOC_Os01g66100 (i.e. the semidwarf gene SD1), a well-known gene controlling plant height (PH) at the adult-plant stage, as the causal gene underlying qSL-1d through gene-based haplotype analysis and knockout transgenic verification. By measuring the phenotypes (SL and PH) of various haplotypes of the two genes and their knockout lines, we found SD1 and LOC_ Os01g68500 controlled both SL and PH, and worked in the same direction, which provided the directly genetic evidence for a positive correlation between SL and PH combined with the analysis of SL and PH in the diverse natural population. Moreover, the knockout transgenic experiments suggested that SD1 had a greater effect on PH compared with LOC_ Os01g68500, but no significant difference in the effect on SL. Further investigation of the pyramiding effects of SD1 and LOC_Os01g68500 based on their haplotype combinations suggested that SD1 may play a dominant role in controlling SL and PH when the two genes coexist. In this study, the effect of SD1 on SL at the seedling stage is validated. In total, two causal genes, SD1 and LOC_ Os01g68500, for SL are cloned in our studies, which controlled both SL and PH, and the suitable haplotypes of SD1 and LOC_ Os01g68500 are beneficial to achieve the desired SL and PH in different rice breeding objectives. These results provide a new clue to develop rice varieties for direct seeding and provide new genetic resources for molecular breeding of rice with suitable PH and strong seedling vigor.

Genetic linkage map construction and QTL analysis for plant height in proso millet (Panicum miliaceum L.)

KEY MESSAGE

A genetic linkage map representing proso millet genome was constructed with SSR markers, and a major QTL corresponding to plant height was mapped on chromosome 14 of this map. Proso millet (Panicum miliaceum L.) has the lowest water requirements of all cultivated cereal crops. However, the lack of a genetic map and the paucity of genomic resources for this species have limited the utility of proso millet for detailed genetic studies and hampered genetic improvement programs. In this study, 97,317 simple sequence repeat (SSR) markers were developed based on the genome sequence of the proso millet landrace Longmi 4. Using some of these markers in conjunction with previously identified SSRs, an SSR-based linkage map for proso millet was successfully constructed using a large mapping population (316 F2 offspring). In total, 186 SSR markers were assigned to 18 linkage groups corresponding to the haploid chromosomes. The constructed map had a total length of 3033.42 centimorgan (cM) covering 78.17% of the assembled reference genome. The length of the 18 linkage groups ranged from 88.89 cM (Chr. 15) to 274.82 cM (Chr. 16), with an average size of 168.17 cM. To our knowledge, this is the first genetic linkage map for proso millet based on SSR markers. Plant height is one of the most important traits in crop improvement. A major QTL was repeatedly detected in different environments, explaining 8.70-24.50% of the plant height variations. A candidate gene affecting auxin biosynthesis and transport, and ROS homeostasis regulation was predicted. Thus, the linkage map and QTL analysis provided herein will promote the development of gene mining and molecular breeding in proso millet.

The ldp1 Mutation Affects the Expression of Auxin-Related Genes and Enhances SAM Size in Rice

Panicle type is one of the important factors affecting rice (Oryza sativa L.) yield, and the identification of regulatory genes in panicle development can provide significant insights into the molecular network involved. This study identified a large and dense panicle 1 (ldp1) mutant produced from the Wuyunjing 7 (WYJ7) genotype, which displayed significant relative increases in panicle length, number of primary and secondary branches, number of grains per panicle, grain width, and grain yield per plant. Scanning electron microscopy results showed that the shoot apical meristem (SAM) of ldp1 was relatively larger at the bract stage (BM), with a significantly increased number of primary (PBM) and secondary branch (SBM) meristematic centers, indicating that the ldp1 mutation affects early stages in SAM development Comparative RNA-Seq analysis of meristem tissues from WYJ7 and ldp1 at the BM, PBM, and SBM developmental stages indicated that the number of differentially expressed genes (DEGs) were highest (1407) during the BM stage. Weighted gene coexpression network analysis (WGCNA) revealed that genes in one module (turquoise) are associated with the ldp1 phenotype and highly expressed during the BM stage, suggesting their roles in the identity transition and branch differentiation stages of rice inflorescences. Hub genes involved in auxin synthesis and transport pathways, such as OsAUX1, OsAUX4, and OsSAUR25, were identified. Moreover, GO and KEGG analysis of the DEGs in the turquoise module and the 1407 DEGs in the BM stage revealed that a majority of genes involved in tryptophan metabolism and auxin signaling pathway were differentially expressed between WYJ and ldp1. The genetic analysis indicated that the ldp1 phenotype is controlled by a recessive monogene (LDP1), which was mapped to a region between 16.9 and 18.1 Mb on chromosome seven. This study suggests that the ldp1 mutation may affect the expression of key genes in auxin synthesis and signal transduction, enhance the size of SAM, and thus affect panicle development. This study provides insights into the molecular regulatory network underlying rice panicle morphogenesis and lays an important foundation for further understanding the function and molecular mechanism of LDP1 during panicle development.

OsNAC103, a NAC Transcription Factor, Positively Regulates Leaf Senescence and Plant Architecture in Rice

Leaf senescence, the last stage of leaf development, is essential for crop yield by promoting nutrition relocation from senescence leaves to new leaves and seeds. NAC (NAM/ATAF1/ATAF2/CUC2) proteins, one of the plant-specific transcription factors, widely distribute in plants and play important roles in plant growth and development. Here, we identified a new NAC member OsNAC103 and found that it plays critical roles in leaf senescence and plant architecture in rice. OsNAC103 mRNA levels were dramatically induced by leaf senescence as well as different phytohormones such as ABA, MeJA and ACC and abiotic stresses including dark, drought and high salinity. OsNAC103 acts as a transcription factor with nuclear localization signals at the N terminal and a transcriptional activation signal at the C terminal. Overexpression of OsNAC103 promoted leaf senescence while osnac103 mutants delayed leaf senescence under natural condition and dark-induced condition, meanwhile, senescence-associated genes (SAGs) were up-regulated in OsNAC103 overexpression (OsNAC103-OE) lines, indicating that OsNAC103 positively regulates leaf senescence in rice. Moreover, OsNAC103-OE lines exhibited loose plant architecture with larger tiller angles while tiller angles of osnac103 mutants decreased during the vegetative and reproductive growth stages due to the response of shoot gravitropism, suggesting that OsNAC103 can regulate the plant architecture in rice. Taken together, our results reveal that OsNAC103 plays crucial roles in the regulation of leaf senescence and plant architecture in rice.

miRNAs and genes as molecular regulators of rice grain morphology and yield

Rice is one of the most consumed crops worldwide and the genetic and molecular basis of its grain yield attributes are well understood. Various studies have identified different yield-related parameters in rice that are regulated by the microRNAs (miRNAs). MiRNAs are endogenous small non-coding RNAs that silence gene expression during or after transcription. They control a variety of biological or genetic activities in plants including growth, development and response to stress. In this review, we have summarized the available information on the genetic control of panicle architecture and grain yield (number and morphology) in rice. The miRNA nodes that are associated with their regulation are also described while focussing on the central role of miR156-SPL node to highlight the co-regulation of two master regulators that determine the fate of panicle development. Since abiotic stresses are known to negatively affect yield, the impact of abiotic stress induced alterations on the levels of these miRNAs are also discussed to highlight the potential of miRNAs for regulating crop yields.

2Gs and plant architecture: breaking grain yield ceiling through breeding approaches for next wave of revolution in rice (Oryza sativa L.)

Rice is a principal food crop for more than half of the global population. Grain number and grain weight (2Gs) are the two complex traits controlled by several quantitative trait loci (QTLs) and are considered the most critical components for yield enhancement in rice. Novel molecular biology and QTL mapping strategies can be utilized in dissecting the complex genetic architecture of these traits. Discovering the valuable genes/QTLs associated with 2Gs traits hidden in the rice genome and utilizing them in breeding programs may bring a revolution in rice production. Furthermore, the positional cloning and functional characterization of identified genes and QTLs may aid in understanding the molecular mechanisms underlying the 2Gs traits. In addition, knowledge of modern genomic tools aids the understanding of the nature of plant and panicle architecture, which enhances their photosynthetic activity. Rice researchers continue to combine important yield component traits (including 2Gs for the yield ceiling) by utilizing modern breeding tools, such as marker-assisted selection (MAS), haplotype-based breeding, and allele mining. Physical co-localization of GW7 (for grain weight) and DEP2 (for grain number) genes present on chromosome 7 revealed the possibility of simultaneous introgression of these two genes, if desirable allelic variants were found in the single donor parent. This review article will reveal the genetic nature of 2Gs traits and use this knowledge to break the yield ceiling by using different breeding and biotechnological tools, which will sustain the world's food requirements.

Characterization and analysis of multi-organ full-length transcriptomes in Sphaeropteris brunoniana and Alsophila latebrosa highlight secondary metabolism and chloroplast RNA editing pattern of tree ferns

BACKGROUND

Sphaeropteris brunoniana and Alsophila latebrosa are both old relict and rare tree ferns, which have experienced the constant changes of climate and environment. However, little is known about their high-quality genetic information and related research on environmental adaptation mechanisms of them. In this study, combined with PacBio and Illumina platforms, transcriptomic analysis was conducted on the roots, rachis, and pinna of S. brunoniana and A. latebrosa to identify genes and pathways involved in environmental adaptation. Additionally, based on the transcriptomic data of tree ferns, chloroplast genes were mined to analyze their gene expression levels and RNA editing events.

RESULTS

In the study, we obtained 11,625, 14,391 and 10,099 unigenes of S. brunoniana root, rachis, and pinna, respectively. Similarly, a total of 13,028, 11,431 and 12,144 unigenes were obtained of A. latebrosa root, rachis, and pinna, respectively. According to the enrichment results of differentially expressed genes, a large number of differentially expressed genes were enriched in photosynthesis and secondary metabolic pathways of S. brunoniana and A. latebrosa. Based on gene annotation results and phenylpropanoid synthesis pathways, two lignin synthesis pathways (H-lignin and G-lignin) were characterized of S. brunoniana. Among secondary metabolic pathways of A. latebrosa, three types of WRKY transcription factors were identified. Additionally, based on transcriptome data obtained in this study, reported transcriptome data, and laboratory available transcriptome data, positive selection sites were identified from 18 chloroplast protein-coding genes of four tree ferns. Among them, RNA editing was found in positive selection sites of four tree ferns. RNA editing affected the protein secondary structure of the rbcL gene. Furthermore, the expression level of chloroplast genes indicated high expression of genes related to the chloroplast photosynthetic system in all four species.

CONCLUSIONS

Overall, this work provides a comprehensive transcriptome resource of S. brunoniana and A. latebrosa, laying the foundation for future tree fern research.

Overexpression of SlCRF6 in tomato inhibits leaf development and affects plant morphology

Cytokinin response factors (CRFs) are transcription factors (TFs) that are specific to plants and have diverse functions in plant growth and stress responses. However, the precise roles of CRFs in regulating tomato plant architecture and leaf development have not been comprehensively investigated. Here, we identified a novel CRF, SlCRF6, which is involved in the regulation of plant growth via the gibberellin (GA) signaling pathway. SlCRF6-overexpressing (SlCRF6-OE) plants displayed pleiotropic phenotypic changes, including reduced internode length and leaf size, which caused dwarfism in tomato plants. This dwarfism could be alleviated by application of exogenous GA3. Remarkably, quantitative real-time PCR (qRTPCR), a dual luciferase reporter assay and a yeast one-hybrid (Y1H) assay revealed that SlCRF6 promoted the expression of SlDELLA (a GA signal transduction inhibitor) in vivo. Furthermore, transgenic plants displayed variegated leaves and diminished chlorophyll content, resulting in decreased photosynthetic efficiency and less starch than in wild-type (WT) plants. The results of transient expression assays and Y1H assays indicated that SlCRF6 suppressed the expression of SlPHAN (leaf morphology-related gene). Collectively, these findings suggest that SlCRF6 plays a crucial role in regulating tomato plant morphology, leaf development, and the accumulation of photosynthetic products.

Genetic architecture and genomic prediction of plant height-related traits in chrysanthemum

Plant height (PH) is a crucial trait determining plant architecture in chrysanthemum. To better understand the genetic basis of PH, we investigated the variations of PH, internode number (IN), internode length (IL), and stem diameter (SD) in a panel of 200 cut chrysanthemum accessions. Based on 330 710 high-quality SNPs generated by genotyping by sequencing, a total of 42 associations were identified via a genome-wide association study (GWAS), and 16 genomic regions covering 2.57 Mb of the whole genome were detected through selective sweep analysis. In addition, two SNPs, Chr1_339370594 and Chr18_230810045, respectively associated with PH and SD, overlapped with the selective sweep regions from FST and π ratios. Moreover, candidate genes involved in hormones, growth, transcriptional regulation, and metabolic processes were highlighted based on the annotation of homologous genes in Arabidopsis and transcriptomes in chrysanthemum. Finally, genomic selection for four PH-related traits was performed using a ridge regression best linear unbiased predictor model (rrBLUP) and six marker sets. The marker set constituting the top 1000 most significant SNPs identified via GWAS showed higher predictabilities for the four PH-related traits, ranging from 0.94 to 0.97. These findings improve our knowledge of the genetic basis of PH and provide valuable markers that could be applied in chrysanthemum genomic selection breeding programs.

BnPLP1 Positively Regulates Flowering Time, Plant Height, and Main Inflorescence Length in Brassica napus

Protein prenylation mediated by the Arabidopsis thaliana PLURIPETALA (AtPLP) gene plays a crucial role in plant growth, development, and environmental response by adding a 15-carbon farnesyl group or one to two 20-carbon geranylgeranyl groups onto one to two cysteine residues at the C-terminus of the target protein. However, the homologous genes and their functions of AtPLP in rapeseed are unclear. In this study, bioinformatics analysis and gene cloning demonstrated the existence of two homologous genes of AtPLP in the Brassica napus L. genome, namely, BnPLP1 and BnPLP2. Evolutionary analysis revealed that BnPLP1 originated from the B. rapa L. genome, while BnPLP2 originated from the B. oleracea L. genome. Genetic transformation analysis revealed that the overexpression of BnPLP1 in Arabidopsis plants exhibited earlier flowering initiation, a prolonged flowering period, increased plant height, and longer main inflorescence length compared to the wild type. Contrarily, the downregulation of BnPLP1 expression in B. napus plants led to delayed flowering initiation, shortened flowering period, decreased plant height, and reduced main inflorescence length compared to the wild type. These findings indicate that the BnPLP1 gene positively regulates flowering time, plant height, and main inflorescence length. This provides a new gene for the genetic improvement of flowering time and plant architecture in rapeseed.

Dormancy-Associated Gene 1 (OsDRM1) as an axillary bud dormancy marker: Retarding Plant Development, and Modulating Auxin Response in Rice (Oryza sativa L.)

Dormancy-Associated Genes 1/Auxin-Repressed Proteins (DRM1/ARP) are associated with bud dormancy, repression of plant growth, and responsiveness to hormones. To further explore the function of DRM1 proteins in rice, we isolated a dormancy-associated gene1 (OsDRM1) through microarray analysis. In situ hybridization analyses revealed that OsDRM1 is predominantly expressed in dormant axillary buds, while it is weakly expressed in growing buds, indicating that OsDRM1 gene can be used as a molecular marker for bud dormancy in rice. Overexpression of OsDRM1 in transgenic plants delayed axillary bud outgrowth by suppressing cell division within the buds. Further studies in OsDRM1-overexpressing transgenic plants showed a reduction in plant height, inhibition of root and hypocotyl elongation, and delayed heading time. Under auxin treatment, overexpression of OsDRM1 in transgenic lines partially rescued the shortened length of the primary and crown root. Taken together, these results indicated that OsDRM1 delayed bud growth by arresting the cell cycle and act as a growth repressor affect rice development by modulated auxin signaling.

GRAS family member LATERAL SUPPRESSOR regulates the initiation and morphogenesis of watermelon lateral organs

The lateral organs of watermelon (Citrullus lanatus), including lobed leaves, branches, flowers, and tendrils, together determine plant architecture and yield. However, the genetic controls underlying lateral organ initiation and morphogenesis remain unclear. Here, we found that knocking out the homologous gene of shoot branching regulator LATERAL SUPPRESSOR in watermelon (ClLs) repressed the initiation of branches, flowers, and tendrils and led to developing round leaves, indicating that ClLs undergoes functional expansion compared with its homologs in Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa), and tomato (Solanum lycopersicum). Using ClLs as the bait to screen against the cDNA library of watermelon, we identified several ClLs-interacting candidate proteins, including TENDRIL (ClTEN), PINOID (ClPID), and APETALA1 (ClAP1). Protein-protein interaction assays further demonstrated that ClLs could directly interact with ClTEN, ClPID, and ClAP1. The mRNA in situ hybridization assay revealed that the transcriptional patterns of ClLs overlapped with those of ClTEN, ClPID, and ClAP1 in the axillary meristems and leaf primordia. Mutants of ClTEN, ClPID, and ClAP1 generated by the CRISPR/Cas9 gene editing system lacked tendrils, developed round leaves, and displayed floral diapause, respectively, and all these phenotypes could be observed in ClLs knockout lines. Our findings indicate that ClLs acts as lateral organ identity protein by forming complexes with ClTEN, ClPID, and ClAP1, providing several gene targets for transforming the architecture of watermelon.

Construction of a High-Density Paulownia Genetic Map and QTL Mapping of Important Phenotypic Traits Based on Genome Assembly and Whole-Genome Resequencing

Quantitative trait locus (QTL) mapping based on a genetic map is a very effective method of marker-assisted selection in breeding, and whole-genome resequencing is one of the useful methods to obtain high-density genetic maps. In this study, the hybrid assembly of Illumina, PacBio, and chromatin interaction mapping data was used to construct high-quality chromosomal genome sequences of Paulownia fortunei, with a size of 476.82 Mb, a heterozygosity of 0.52%, and a contig and scaffold N50s of 7.81 Mb and 21.81 Mb, respectively. Twenty scaffolds with a total length of 437.72 Mb were assembled into 20 pseudochromosomes. Repeat sequences with a total length of 243.96 Mb accounted for 51.16% of the entire genome. In all, 26,903 protein-coding gene loci were identified, and 26,008 (96.67%) genes had conserved functional motifs. Further comparative genomics analysis preliminarily showed that the split of P. fortunei with Tectona grandis likely occurred 38.8 (33.3-45.1) million years ago. Whole-genome resequencing was used to construct a merged genetic map of 20 linkage groups, with 2993 bin markers (3,312,780 SNPs), a total length of 1675.14 cm, and an average marker interval of 0.56 cm. In total, 73 QTLs for important phenotypic traits were identified (19 major QTLs with phenotypic variation explained ≥ 10%), including 10 for the diameter at breast height, 7 for the main trunk height, and 56 for branch-related traits. These results not only enrich P. fortunei genomic data but also form a solid foundation for fine QTL mapping and key marker/gene mining of Paulownia, which is of great significance for the directed genetic improvement of these species.

Unlocking the Multifaceted Mechanisms of Bud Outgrowth: Advances in Understanding Shoot Branching

Shoot branching is a complex and tightly regulated developmental process that is essential for determining plant architecture and crop yields. The outgrowth of tiller buds is a crucial step in shoot branching, and it is influenced by a variety of internal and external cues. This review provides an extensive overview of the genetic, plant hormonal, and environmental factors that regulate shoot branching in several plant species, including rice, Arabidopsis, tomato, and wheat. We especially highlight the central role of TEOSINTE BRANCHED 1 (TB1), a key gene in orchestrating bud outgrowth. In addition, we discuss how the phytohormones cytokinins, strigolactones, and auxin interact to regulate tillering/branching. We also shed light on the involvement of sugar, an integral component of plant development, which can impact bud outgrowth in both trophic and signaling ways. Finally, we emphasize the substantial influence of environmental factors, such as light, temperature, water availability, biotic stresses, and nutrients, on shoot branching. In summary, this review offers a comprehensive evaluation of the multifaced regulatory mechanisms that underpin shoot branching and highlights the adaptable nature of plants to survive and persist in fluctuating environmental conditions.

Identification and characterization of the cupin_1 domain-containing proteins in ma bamboo (Dendrocalamus latiflorus) and their potential role in rhizome sprouting

Cupin_1 domain-containing protein (CDP) family, which is a member of the cupin superfamily with the most diverse functions in plants, has been found to be involved in hormone pathways that are closely related to rhizome sprouting (RS), a vital form of asexual reproduction in plants. Ma bamboo is a typical clumping bamboo, which mainly reproduces by RS. In this study, we identified and characterized 53 Dendrocalamus latiflorus CDP genes and divided them into seven subfamilies. Comparing the genetic structures among subfamilies showed a relatively conserved gene structure within each subfamily, and the number of cupin_1 domains affected the conservation among D. latiflorus CDP genes. Gene collinearity results showed that segmental duplication and tandem duplication both contributed to the expansion of D. latiflorus CDP genes, and lineage-specific gene duplication was an important factor influencing the evolution of CDP genes. Expression patterns showed that CDP genes generally had higher expression levels in germinating underground buds, indicating that they might play important roles in promoting shoot sprouting. Transcription factor binding site prediction and co-expression network analysis indicated that D. latiflorus CDPs were regulated by a large number of transcription factors, and collectively participated in rhizome buds and shoot development. This study significantly provided new insights into the evolutionary patterns and molecular functions of CDP genes, and laid a foundation for further studying the regulatory mechanisms of plant rhizome sprouting.

ZmBELL10 interacts with other ZmBELLs and recognizes specific motifs for transcriptional activation to modulate internode patterning in maize

Plant height is an important agronomic trait that affects crop yield. Elucidating the molecular mechanism underlying plant height regulation is also an important question in developmental biology. Here, we report that a BELL transcription factor, ZmBELL10, positively regulates plant height in maize (Zea mays). Loss of ZmBELL10 function resulted in shorter internodes, fewer nodes, and smaller kernels, while ZmBELL10 overexpression increased plant height and hundred-kernel weight. Transcriptome analysis and chromatin immunoprecipitation followed by sequencing showed that ZmBELL10 recognizes specific sequences in the promoter of its target genes and activates cell division- and cell elongation-related gene expression, thereby influencing node number and internode length in maize. ZmBELL10 interacted with several other ZmBELL proteins via a spatial structure in its POX domain to form protein complexes involving ZmBELL10. All interacting proteins recognized the same DNA sequences, and their interaction with ZmBELL10 increased target gene expression. We identified the key residues in the POX domain of ZmBELL10 responsible for its protein-protein interactions, but these residues did not affect its transactivation activity. Collectively, our findings shed light on the functions of ZmBELL10 protein complexes and provide potential targets for improving plant architecture and yield in maize.

The transcription factor SPL13 mediates strigolactone suppression of shoot branching by inhibiting cytokinin synthesis in Solanum lycopersicum

Plant architecture imposes a large impact on crop yield. IDEAL PLANT ARCHITECTURE 1 (IPA1), which encodes a SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factor, is a target of molecular design for improving grain yield. However, the roles of SPL transcription factors in regulating tomato (Solanum lycopersicum) plant architecture are unclear. Here, we show that the expression of SPL13 is down-regulated in the lateral buds of strigolactone (SL)-deficient ccd mutants and is induced by GR24 (a synthetic analog of SL). Knockout of SPL13 by CRISPR/Cas9 resulted in higher levels of cytokinins (CKs) and transcripts of the CK synthesis gene ISOPENTENYL TRANSFERASES 1 (IPT1) in the stem nodes, and more growth of lateral buds. GR24 suppresses CK synthesis and lateral bud growth in ccd mutants, but is not effective in spl13 mutants. On the other hand, silencing of the IPT1 gene inhibited bud growth of spl13 mutants. Interestingly, SL levels in root extracts and exudates are significantly increased in spl13 mutants. Molecular studies indicated that SPL13 directly represses the transcription of IPT1 and the SL synthesis genes CAROTENOID CLEAVAGE DIOXYGENASE 7 (CCD7) and MORE AXILLARY GROWTH 1 (MAX1). The results demonstrate that SPL13 acts downstream of SL to suppress lateral bud growth by inhibiting CK synthesis in tomato. Tuning the expression of SPL13 is a potential approach for decreasing the number of lateral shoots in tomato.

Alterations in Growth Habit to Channel End-of-Season Perennial Reserves towards Increased Yield and Reduced Regrowth after Defoliation in Upland Cotton (Gossypium hirsutum L.)

Cotton (Gossypium spp.) is the primary source of natural textile fiber in the U.S. and a major crop in the Southeastern U.S. Despite constant efforts to increase the cotton fiber yield, the yield gain has stagnated. Therefore, we undertook a novel approach to improve the cotton fiber yield by altering its growth habit from perennial to annual. In this effort, we identified genotypes with high-expression alleles of five floral induction and meristem identity genes (FT, SOC1, FUL, LFY, and AP1) from an Upland cotton mini-core collection and crossed them in various combinations to develop cotton lines with annual growth habit, optimal flowering time, and enhanced productivity. To facilitate the characterization of genotypes with the desired combinations of stacked alleles, we identified molecular markers associated with the gene expression traits via genome-wide association analysis using a 63 K SNP Array. Over 14,500 SNPs showed polymorphism and were used for association analysis. A total of 396 markers showed associations with expression traits. Of these 396 markers, 159 were mapped to genes, 50 to untranslated regions, and 187 to random genomic regions. Biased genomic distribution of associated markers was observed where more trait-associated markers mapped to the cotton D sub-genome. Many quantitative trait loci coincided at specific genomic regions. This observation has implications as these traits could be bred together. The analysis also allowed the identification of candidate regulators of the expression patterns of these floral induction and meristem identity genes whose functions will be validated.

Tomato miR156-targeted SlSBP15 represses shoot branching by modulating hormone dynamics and interacting with GOBLET and BRANCHED1b

The miRNA156 (miR156)/SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL/SBP) regulatory hub is highly conserved among phylogenetically distinct species, but how it interconnects multiple pathways to converge to common integrators controlling shoot architecture is still unclear. Here, we demonstrated that the miR156/SlSBP15 node modulates tomato shoot branching by connecting multiple phytohormones with classical genetic pathways regulating both axillary bud development and outgrowth. miR156-overexpressing plants (156-OE) displayed high shoot branching, whereas plants overexpressing a miR156-resistant SlSBP15 allele (rSBP15) showed arrested shoot branching. Importantly, the rSBP15 allele was able to partially restore the wild-type shoot branching phenotype in the 156-OE background. rSBP15 plants have tiny axillary buds, and their activation is dependent on shoot apex-derived auxin transport inhibition. Hormonal measurements revealed that indole-3-acetic acid (IAA) and abscisic acid (ABA) concentrations were lower in 156-OE and higher in rSBP15 axillary buds, respectively. Genetic and molecular data indicated that SlSBP15 regulates axillary bud development and outgrowth by inhibiting auxin transport and GOBLET (GOB) activity, and by interacting with tomato BRANCHED1b (SlBRC1b) to control ABA levels within axillary buds. Collectively, our data provide a new mechanism by which the miR156/SPL/SBP hub regulates shoot branching, and suggest that modulating SlSBP15 activity might have potential applications in shaping tomato shoot architecture.

Diversification of plant SUPPRESSOR OF MAX2 1 (SMAX1)-like genes and genome-wide identification and characterization of cotton SMXL gene family

BACKGROUND

Strigolactones (SLs) are a recently discovered class of plant hormones. SUPPRESSOR OF MAX2 1 (SMAX1)-like proteins, key component of the SL signaling pathway, have been studied extensively for their roles in regulating plant growth and development, such as plant branching. However, systematic identification and functional characterization of SMXL genes in cotton (Gossypium sp.), an important fiber and oil crop, has rarely been conducted.

RESULTS

We identified 210 SMXL genes from 21 plant genomes and examined their evolutionary relationships. The structural characteristics of the SMXL genes and their encoded proteins exhibited both consistency and diversity. All plant SMXL proteins possess a conserved Clp-N domain, P-loop NTPase, and EAR motif. We identified 63 SMXL genes in cotton and classified these into four evolutionary branches. Gene expression analysis revealed tissue-specific expression patterns of GhSMXL genes, with some upregulated in response to GR24 treatment. Protein co-expression network analysis showed that GhSMXL6, GhSMXL7-1, and GhSMXL7-2 mainly interact with proteins functioning in growth and development, while virus-induced gene silencing revealed that GhSMAX1-1 and GhSMAX1-2 suppress the growth and development of axillary buds.

CONCLUSIONS

SMXL gene family members show evolutionary diversification through the green plant lineage. GhSMXL6/7-1/7-2 genes play critical roles in the SL signaling pathway, while GhSMXL1-1 and GhSMXL1-2 function redundantly in growth of axillary buds. Characterization of the cotton SMXL gene family provides new insights into their roles in responding to SL signals and in plant growth and development. Genes identified in this study could be used as the candidate genes for improvement of plant architecture and crop yield.