Genome-wide binding analysis of the transcription activator ideal plant architecture1 reveals a complex network regulating rice plant architecture

Time-course transcriptome and chromatin accessibility analyses reveal the dynamic transcriptional regulation shaping spikelet hull size

The grains of rice (Oryza sativa) are enclosed by a spikelet hull comprising the lemma and palea. Development of the spikelet hull determines the storage capacity of the grain, thus affecting grain yield and quality. Although multiple signaling pathways controlling grain size have been identified, the transcriptional regulatory mechanisms underlying grain development remain limited. Here, we used RNA-seq and ATAC-seq to characterize the transcription and chromatin accessibility dynamics during the development of spikelet hulls. A time-course analysis showed that more than half of the genes were sequentially expressed during hull development and that the accessibility of most open chromatin regions (OCRs) changed moderately, although some regions positively or negatively affected the expression of their closest genes. We revealed a crucial role of GROWTH-REGULATING FACTORs in shaping grain size by influencing multiple metabolic and signaling pathways, and a coordinated transcriptional regulation in response to auxin and cytokinin signaling. We also demonstrated the function of SCL6-IIb, a member of the GRAS family transcription factors, in regulating grain size, with SCL6-IIb expression being activated by SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 18 (OsSPL18). When we edited the DNA sequences within OCRs upstream of the start codon of BRASSINAZOLE-RESISTANT 1 (BZR1) and SCL6-IIb, we generated multiple mutant lines with longer grains. These findings offer a comprehensive overview of the cis-regulatory landscape involved in forming grain capacity and a valuable resource for exploring the regulatory network behind grain development.

Mutation of strigolactone biosynthetic gene DWARF 17 impairs the responses of rice tillering to N supply

Tiller number is one important parameter for rice yield and is influenced by both strigolactone (SL) and nitrogen (N). However, how SL and N interact to regulate the tiller outgrowth in rice is unclear. In this study, we isolated a multi-tillering mutant, tin, from an ethyl methanesulfonate (EMS)-mutagenized population of Wuyunjing 7, a japonica cultivar. The tin mutant exhibited low sensitivity to varying N concentrations during the tiller development. Through bulk segregation analysis (BSA), we identified a missense mutation located in the exon of DWARF 17 (D17), a key gene involved in SL biosynthesis. Complementation experiments confirmed that D17 is responsible for the tin tiller phenotype, and exogenous application of the SL analogue GR24 restored the tiller response of tin to N. Transcriptome analysis further revealed that D17 and SL regulate the tiller response to N by modulating the expression of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes and ammonium transporter genes. These findings elucidate the mechanism by which SL and N coordinate to regulate rice tillering growth, providing valuable insights for optimizing rice plant architecture to enhance yield potential.

A DOF transcription factor GLW9/OsDOF25 regulates grain shape and tiller angle in rice

Grain shape and tiller angle are two important agronomic traits influencing grain yield and quality in rice. Herein, we map-based cloned a grain shape gene GLW9 (Grain Length and Width on chromosome 9), which encodes a DNA binding with one finger (DOF) family transcription factor OsDOF25. GLW9 positively regulates grain length and negatively regulates grain width, consequently improving grain length-to-width ratio and appearance quality. GLW9 binds to the EXPA6 promotor to upregulate its expression, thereby positively regulating cell expansion and grain shape. On the other hand, GLW9 directly upregulates the expression of OsPIN1b to reduce tiller angle. This study elucidates the mechanism by which GLW9 coordinately regulates grain shape and tiller angle, providing theoretical reference and gene resources for the improvement of grain shape and tiller angle in rice.

PpSPL1 and PpSPL15 inhibit peach branching by increasing strigolactone synthesis

MAIN CONCLUSION

PpSPL1 and PpSPL15 inhibit peach branching by directly binding to and upregulating the expression of strigolactone (SL) synthesis gene PpLBO1. Branch number is a crucial agronomic trait that influences tree architecture, directly affecting fruit yield and quality. It remains unknown whether SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL), an important transcription factor in determining plant architecture, is involved in the peach branching process. In this study, we found that PpSPL1 and PpSPL15 exhibited significantly higher expression levels in pillar type peach 'Sahonglongzhu' (with fewer secondary branches) compared to standard-type peach 'Okubo' (with more secondary branches). PpSPL1 and PpSPL15 can directly bind to the promoter of the SL synthesis gene PpLBO1. Transient overexpression of PpSPL1 and PpSPL15 in 'Sahonglongzhu' peach axillary buds significantly increased the expression of PpLBO1 and endogenous SL content. Conversely, opposite results were obtained when the expression of PpSPL1 and PpSPL15 was transiently silenced in peach axillary buds. Gene function analysis indicated that transient overexpression of PpSPL1 and PpSPL15 in peach seedlings clearly inhibited peach branching. On the contrary, the number of branches dramatically increased when the expression of PpSPL1 and PpSPL15 were transiently silenced in peach seedlings. These results suggested that PpSPL1 and PpSPL15 could bind to and enhance the expression of PpLBO1, further inhibiting peach branching.

GS2 cooperates with IPA1 to control panicle architecture

Panicle size and grain number are important agronomic traits that determine grain yield in rice. However, the underlying mechanism regulating panicle size and grain number remains largely unknown. Here, we report that GS2 plays an important role in regulating panicle architecture. The RNAi of GS2™ (target site mutation, TM) produced erect and dense panicle with increased primary and secondary branches and grain number per panicle, whereas the overexpression of GS2™ showed longer panicles and fewer grains than wild-type. GS2 directly binds to the GCCA motif and significantly enhances the transcriptional activation ability through the interaction with IPA1. DEP1 is a common target gene of GS2 and IPA1 in regulating branch number and grain number per panicle. The pyramiding of GS2™ and IPA1™1 (Target site mutation1, TM1) on hybrid rice can significantly increase rice yield. Our findings reveal the novel function of GS2 and the molecular mechanism of GS2/IPA1-DEP1 module in controlling panicle architecture.

Genome-wide analysis of Q binding reveals a regulatory network that coordinates wheat grain yield and grain protein content

Wheat is an important cereal crop used to produce diverse and popular food worldwide because of its high grain yield (GY) and grain protein content (GPC). However, GY and GPC are usually negatively correlated. We previously reported that favorable alleles of the wheat domestication gene Q can synchronously increase GY and GPC, but the underlying mechanisms remain largely unknown. In this study, we investigated the regulatory network involving Q associated with GY and GPC in young grains through DNA affinity purification sequencing and transcriptome sequencing analyses, electrophoretic mobility shift and dual-luciferase assays, and transgenic approaches. Three Q-binding motifs, namely TTAAGG, AAACA[A/T]A, and GTAC[T/G]A, were identified. Notably, genes related to photosynthesis or carbon and nitrogen metabolism were enriched and regulated by Q. Moreover, Q was revealed to bind directly to its own gene and the glutamine synthetase gene TaGSr-4D to increase expression, thereby influencing nitrogen assimilation during the grain filling stage and increasing GPC. Considered together, our study findings provide molecular evidence of the positive regulatory effects of Q on wheat GY and GPC.

The OsNL1-OsTOPLESS2-OsMOC1/3 pathway regulates high-order tiller outgrowth in rice

Tiller is an important factor in determining rice yield. Currently, researches mainly focus on the outgrowth of low-order tiller (LOT), while the regulation mechanism of high-order tiller (HOT) outgrowth has remained unknown. In this study, we detected one OsNL1 mutant, nl1, exhibiting HOT numbers increase, and found that OsNL1 interacts with OsTOPLESS2, which was mediated by the core motif of nine amino acids VDCTLSLGT within the HAN domain of OsNL1. The topless2 mutant exhibits similar HOT number increase as in the nl1. Through ChIP-seq analysis, we revealed that OsNL1 recruits OsTOPLESS2 to conduct histone deacetylation in the promoters of OsMOC1 and OsMOC3 to regulate HOT outgrowth. Moreover, we showed that the HAN domain is essential for OsNL1 function as a repressor. In summary, our study reveals partial mechanism of HOT outgrowth in rice and deciphers the molecular biology function of the HAN domain. This will contribute to the comprehensive understanding of tiller outgrowth and the role of HAN-domain-containing genes.

Enhancing crop yields to ensure food security by optimizing photosynthesis

The crop yields achieved through traditional plant breeding techniques appear to be nearing a plateau. Therefore, it is essential to accelerate advancements in photosynthesis, the fundamental process by which plants convert light energy into chemical energy, to further enhance crop yields. Research focused on improving photosynthesis holds significant promise for increasing sustainable agricultural productivity and addressing challenges related to global food security. This review examines the latest advancements and strategies aimed at boosting crop yields by enhancing photosynthetic efficiency. There has been a linear increase in yield over the years in historically released germplasm selected through traditional breeding methods, and this increase is accompanied by improved photosynthesis. We explore various aspects of the light reactions designed to enhance crop yield, including light harvest efficiency through smart canopy systems, expanding the absorbed light spectrum to include far-red light, optimizing non-photochemical quenching, and accelerating electron transport flux. At the same time, we investigate carbon reactions that can enhance crop yield, such as manipulating Rubisco activity, improving the Calvin-Benson-Bassham (CBB) cycle, introducing CO2 concentrating mechanisms (CCMs) in C3 plants, and optimizing carbon allocation. These strategies could significantly impact crop yield enhancement and help bridge the yield gap.

The role of Ancestral MicroRNAs in grass inflorescence development

Plant inflorescences are complex, highly diverse structures whose morphology is determined in meristems that form during reproductive development. Inflorescence structure influences flower formation, and consequently grain number, and yield in crops. Correct inflorescence and flower development require tight control of gene expression via complex interplay between regulatory networks. MicroRNAs (miRNAs) have emerged as fundamental modulators of gene expression at the transcriptional and/or post-transcriptional level in plant inflorescence development. First discovered more than three decades ago, miRNAs have proved to be revolutionary in advancing our mechanistic understanding of gene expression. This review highlights current knowledge of downstream target genes and pathways of some highly conserved miRNAs that regulate the maintenance, identity, and activity of inflorescence and floral meristems in economically and agriculturally important grass species, including rice (Oryza sativa), maize (Zea mays), barley (Hordeum vulgare), and wheat (Triticum aestivum). Furthermore, we summarize emerging regulatory networks of miRNAs and their targets to suggest new avenues and strategies for application of miRNAs as a tool to enhance crop yield and performance.

Regulation of tillering and panicle branching in rice and wheat

Branching is a critical aspect of plant architecture that significantly impacts the yield and adaptability of staple cereal crops like rice and wheat. Cereal crops develop tillers during the vegetative stage and panicle or spike branches during the reproductive stage, respectively, both of which are significantly impacted by hormones and genetic factors. Tillering and panicle branching are closely interconnected and exhibit high environmental plasticity. Here, we summarize the recent progress in genetic, hormonal, and environmental factors regulation in the branching of rice and wheat. This review not only provides a comprehensive overview of the current knowledge on branching mechanisms in rice and wheat, but also explores the prospects for future research aimed at optimizing crop architecture for enhanced productivity.

Combining two main NAL1 functional alleles can increase rice yield

NARROW LEAF1 (NAL1) is one of the key genes in regulating photosynthesis and plant architecture. As the antagonistic effects of NAL1 have concurrent impacts on photosynthesis and yield component traits, how we can effectively utilize the NAL1 gene to further increase rice yield is not clear. In this study, we used two different main functional NAL1 alleles, each of which has previously been proven to have specifically advantageous traits, and tested whether the combined NAL1 alleles have a higher yield than the homozygous alleles. Our results exhibited that the combined NAL1 alleles had better parent heterosis (BPH) for panicle number and the total filled grain number per plant, and had middle parent heterosis (MPH) for spikelet number per panicle without affecting thousand-grain weight when compared with the homozygous alleles. In consequence, the NAL1 hybrid plants displayed highly increased grain yield compared with both homozygous parents. The hybrid plants also had better plant architecture and higher canopy photosynthesis. Western blot and proteomics results showed the hybrid plants had a middle abundant NAL1 protein level, and the upregulated proteins were mainly involved in the nucleus and DNA binding process but the downregulated proteins were mainly involved in the oxidation-reduction process, single-organism metabolic process, and fatty acid biosynthetic process. Furthermore, the hybrid vigor effect of NAL1 was confirmed by substituting the mutual male parent 9311 with 9311-NIL in two super hybrid rice varieties (LYP9 and YLY1). This study demonstrates that we can achieve a higher level of grain production in hybrid rice by using the heterosis of NAL1.

Mechanism of zju-miR156c-mediated network in regulating witches' broom symptom of Chinese jujube

Jujube witches' broom, caused by phytoplasma, is a destructive disease of Chinese jujube. Studies have shown that zju-miR156s play an important role in phytoplasma infection in jujube, but the regulatory mechanism between zju-miR156c and witches' broom remains unexplored. In the current study, miRNA-seq and gene expression analysis showed that zju-miR156c was more highly induced in infected jujube plants than the other miRNAs and its target gene was ZjSPL3. In addition, the expression levels of thymidylate kinase gene (TMKJWB) and secreted jujube protein (SJP1JWB) in diseased materials were higher than those in healthy controls. The expression level of zju-miR156c was significantly upregulated, while ZjSPL3 was sharply downregulated and the content of cytokinin (CTK) significantly increased. Overexpression of zju-miR156c in Arabidopsis significantly reduced the expression of AtSPL10 (homologous gene of ZjSPL3) but increased the content of CTK, and the transgenic plants exhibited witches' broom symptoms. In addition, yeast two-hybrid and co-immunoprecipitation assays confirmed that SJP1JWB interacted with ZjERF18. Yeast one-hybrid analysis showed that ZjERF18 could interact with the promoter of zju-MIR156c. In conclusion, our results demonstrated a novel pathogenic module of ZjERF18-zju-miR156c-ZjSPL3-CTK has an important function in the formation of witches' broom caused by SJP1JWB.

Loss of OsSPL8 Function Confers Improved Resistance to Glufosinate and Abiotic Stresses in Rice

Weeds are among the most significant factors contributing to decreases in crop yield and quality. Glufosinate, a nonselective, broad-spectrum herbicide, has been extensively utilized for weed control in recent decades. However, crops are usually sensitive to glufosinate. Therefore, the development of glufosinate-resistant crops is crucial for effective weed management in agriculture. In this study, we characterized a SQUAMOSA promoter-binding-like (SPL) factor, OsSPL8, which acts as a negative regulator of glufosinate resistance by inhibiting the transcription of OsGS1;1 and OsGS2 and consequently reducing GS activity. Furthermore, the loss of OsSPL8 function enhanced tolerance to drought and salt stresses. Transcriptomic comparisons between the gar18-3 mutant and wild type revealed that OsSPL8 largely downregulates stress-responsive genes and upregulates growth-related genes. We demonstrated that OsSPL8 directly regulates OsOMTN6 and OsNAC17, which influence drought tolerance. In addition, OsSPL8 directly represses the expression of salt stress tolerance-related genes such as OsHKT1.1 and OsTPP1. Collectively, our results demonstrate that OsSPL8 is a negative regulator of both glufosinate resistance and abiotic stress tolerance.

The phosphatidylethanolamine-binding proteins OsMFT1 and OsMFT2 regulate seed dormancy in rice

Seed dormancy is crucial for optimal plant life-cycle timing. However, domestication has largely diminished seed dormancy in modern cereal cultivars, leading to challenges such as preharvest sprouting (PHS) and subsequent declines in yield and quality. Therefore, it is imperative to unravel the molecular mechanisms governing seed dormancy for the development of PHS-resistant varieties. In this study, we screened a mutant of BASIC HELIX-LOOP-HELIX TRANSCRIPTION FACTOR4 (OsbHLH004) with decreased seed dormancy and revealed that OsbHLH004 directly regulates the expression of 9-CIS-EPOXYCAROTENOID DIOXYGENASE3 (OsNCED3) and GIBBERELLIN 2-OXIDASE6 (OsGA2ox6) in rice (Oryza sativa). Additionally, we determined that two phosphatidylethanolamine-binding proteins, MOTHER OF FT AND TFL1 and 2 (OsMFT1 and OsMFT2; hereafter OsMFT1/2) interact with OsbHLH004 and Ideal Plant Architecture 1 (IPA1) to regulate their binding capacities on OsNCED3 and OsGA2ox6, thereby promoting seed dormancy. Intriguingly, FT-INTERACTING PROTEIN1 (OsFTIP1) interacts with OsMFT1/2 and affects their nucleocytoplasmic translocation into the nucleus, where OsMFT1/2-OsbHLH004 and OsMFT1/2-IPA1 antagonistically modulate the expression of OsNCED3 and OsGA2ox6. Our findings reveal that OsFTIP1-mediated inhibition of nuclear translocation of OsMFT1/2 and the dynamic transcriptional modulation of OsNCED3 and OsGA2ox6 by OsMFT1/2-OsbHLH004 and OsMFT1/2-IPA1 complexes in seed dormancy in rice.

Fine-tuning of IPA1 transactivation activity by E3 ligase IPI7-mediated non-proteolytic K29-ubiquitination during Magnaporthe oryzae infection

The Ideal Plant Architecture 1 (IPA1) transcription factor promotes rice yield and immunity through phosphorylation at its amino acid residue Ser163 as a switch. Although phosphorylated IPA1 mimic, IPA1(S163D), directly targets the promoter of immune response gene WRKY45, it cannot activate its expression. Here, we identified a co-activator of IPA1(S163D), a RING-finger E3 ligase IPA1 interactor 7 (IPI7), which fine-tunes the transcriptional activity of IPA1 to timely promote plant immunity and simultaneously maintain growth for yield. IPI7 interacts with IPA1 and promotes K29-polyubiquitination of IPA1 in vitro and in vivo. However, the stability of IPA1 protein is not affected by IPI7-mediated ubiquitination. The IPI7-promoted K29-polyubiquitination of IPA1 is induced by Magnaporthe oryzae infection and required for phosphorylated IPA1 to transactivate WRKY45 expression for immune response but not for plain IPA1 to transactivate DENSE AND ERECT PANICLES 1 (DEP1) expression for panicle development. IPI7 knockout impairs IPA1-mediated immunity but not yield. Our study reveals that plants utilize non-proteolytic K29-ubiquitination as a response to pathogen infection to fine-tune IPA1 transactivation activity for promoting immunity.

The TaGW2-TaSPL14 module regulates the trade-off between tiller number and grain weight in wheat

IDEAL PLANT ARCHITECTURE1 (IPA1) is a pivotal gene controlling plant architecture and grain yield. However, little is known about the effects of Triticum aestivum SQUAMOSA PROMOTER-BINDING-LIKE 14 (TaSPL14), an IPA1 ortholog in wheat, on balancing yield traits and its regulatory mechanism in wheat (T. aestivum L.). Here, we determined that the T. aestivum GRAIN WIDTH2 (TaGW2)-TaSPL14 module influences the balance between tiller number and grain weight in wheat. Overexpression of TaSPL14 resulted in a reduced tiller number and increased grain weight, whereas its knockout had the opposite effect, indicating that TaSPL14 negatively regulates tillering while positively regulating grain weight. We further identified TaGW2 as a novel interacting protein of TaSPL14 and confirmed its ability to mediate the ubiquitination and degradation of TaSPL14. Based on our genetic evidence, TaGW2 acts as a positive regulator of tiller number, in addition to its known role as a negative regulator of grain weight, which is opposite to TaSPL14. Moreover, combinations of TaSPL14-7A and TaGW2-6A haplotypes exhibit significantly additive effects on tiller number and grain weight in wheat breeding. Our findings provide insight into how the TaGW2-TaSPL14 module regulates the trade-off between tiller number and grain weight and its potential application in improving wheat yield.

The AGAMOUS-LIKE 16-GENERAL REGULATORY FACTOR 1 module regulates axillary bud outgrowth via catabolism of abscisic acid in cucumber

Lateral branches are important components of shoot architecture and directly affect crop yield and production cost. Although sporadic studies have implicated abscisic acid (ABA) biosynthesis in axillary bud outgrowth, the function of ABA catabolism and its upstream regulators in shoot branching remain elusive. Here, we showed that the MADS-box transcription factor AGAMOUS-LIKE 16 (CsAGL16) is a positive regulator of axillary bud outgrowth in cucumber (Cucumis sativus). Functional disruption of CsAGL16 led to reduced bud outgrowth, whereas overexpression of CsAGL16 resulted in enhanced branching. CsAGL16 directly binds to the promoter of the ABA 8'-hydroxylase gene CsCYP707A4 and promotes its expression. Loss of CsCYP707A4 function inhibited axillary bud outgrowth and increased ABA levels. Elevated expression of CsCYP707A4 or treatment with an ABA biosynthesis inhibitor largely rescued the Csagl16 mutant phenotype. Moreover, cucumber General Regulatory Factor 1 (CsGRF1) interacts with CsAGL16 and antagonizes CsAGL16-mediated CsCYP707A4 activation. Disruption of CsGRF1 resulted in elongated branches and decreased ABA levels in the axillary buds. The Csagl16 Csgrf1 double mutant exhibited a branching phenotype resembling that of the Csagl16 single mutant. Therefore, our data suggest that the CsAGL16-CsGRF1 module regulates axillary bud outgrowth via CsCYP707A4-mediated ABA catabolism in cucumber. Our findings provide a strategy to manipulate ABA levels in axillary buds during crop breeding to produce desirable branching phenotypes.

Modulation of histone acetylation enables fully mechanized hybrid rice breeding

Hybrid rice has achieved high grain yield and greatly contributes to food security, but the manual-labour-intensive hybrid seed production process limits fully mechanized hybrid rice breeding. For next-generation hybrid seed production, the use of small-grain male sterile lines to mechanically separate small hybrid seeds from mixed harvest is promising. However, it is difficult to find ideal grain-size genes for breeding ideal small-grain male sterile lines without penalties in the number of hybrid seeds and hybrid rice yield. Here we report that the use of small-grain alleles of the ideal grain-size gene GSE3 in male sterile lines enables fully mechanized hybrid seed production and dramatically increases hybrid seed number in three-line and two-line hybrid rice systems. The GSE3 gene encodes a histone acetyltransferase that binds histones and influences histone acetylation levels. GSE3 is recruited by the transcription factor GS2 to the promoters of their co-regulated grain-size genes and influences the histone acetylation status of their co-regulated genes. Field trials demonstrate that genome editing of GSE3 can be used to immediately improve current elite male sterile lines of hybrid rice for fully mechanized hybrid rice breeding, providing a new perspective for mechanized hybrid breeding in other crops.

Selenium and other heavy metal levels in different rice brands commonly consumed in Pretoria, South Africa

For centuries, rice has been a dietary staple food partially due to its accessibility, affordability, and nutritional content. However, it has been documented that plants can bioaccumulate trace elements from soil and store them in their tissues therefore necessitating monitoring of its nutritional quality. The current study investigated the Selenium and heavy metal contents of various brands of rice obtained from different retail stores in Pretoria, South Africa. The analysis was carried out using different rice samples and different methods/stages of cooking rice including the analysis of rinsed rice water (RW), raw rice (RR), cooked rice (CR), and cooked rice water (CW), for trace elements content using the Inductive Couple Plasma Mass Spectrometry. The results revealed that the Se content ranged from 0.013 ± 0.01 mg/kg - 0.089 ± 0.06 mg/kg in RR, 0.013 ± 0.01 mg/kg - 0.046 ± 0.01 mg/kg in CR, 0.01 ± 0.01mg/kg- 0.028 ± 0.00 mg/kg in RW and 0.01 ± 0.01 mg/kg - 0.048 ± 0.01 mg/kg in CW. The calculated estimated dietary intake (EDI) of Se was recorded as follows; raw rice (7.06 × 10-5 mg/day), cooked rice (5.01 × 10-5 mg/day), water from cooked rice (4.54 × 10-5 mg/day) and rinsed water of raw rice (3.97 × 10-5 mg/day). The concentrations of all other heavy metals measured were within the WHO-recommended limits. The HQ for all the trace metals in all the samples did not exceed one, implying that there is no health risk from trace metals analysed in this study from the consumption of the rice brands used in this study. The results of this study demonstrated that reliance on rice alone for the supply of Se may be inadequate owing to the values obtained in our study. Constant monitoring of the nutritional contents of food products may be required to improve the overall nutritional well-being of the consumers.

MtTCP18 Regulates Plant Structure in Medicago truncatula

Plant structure has a large influence on crop yield formation, with branching and plant height being the important factors that make it up. We identified a gene, MtTCP18, encoding a TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) transcription factor highly conserved with Arabidopsis gene BRC1 (BRANCHED1) in Medicago truncatula. Sequence analysis revealed that MtTCP18 included a conserved basic helix-loop-helix (BHLH) motif and R domain. Expression analysis showed that MtTCP18 was expressed in all organs examined, with relatively higher expression in pods and axillary buds. Subcellular localization analysis showed that MtTCP18 was localized in the nucleus and exhibited transcriptional activation activity. These results supported its role as a transcription factor. Meanwhile, we identified a homozygous mutant line (NF14875) with a mutation caused by Tnt1 insertion into MtTCP18. Mutant analysis showed that the mutation of MtTCP18 altered plant structure, with increased plant height and branch number. Moreover, we found that the expression of auxin early response genes was modulated in the mutant. Therefore, MtTCP18 may be a promising candidate gene for breeders to optimize plant structure for crop improvement.

Switching action modes of miR408-5p mediates auxin signaling in rice

MicroRNAs (miRNAs) play fundamental roles in many developmental and physiological processes in eukaryotes. MiRNAs in plants generally regulate their targets via either mRNA cleavage or translation repression; however, which approach plays a major role and whether these two function modes can shift remains elusive. Here, we identify a miRNA, miR408-5p that regulates AUXIN/INDOLE ACETIC ACID 30 (IAA30), a critical repressor in the auxin pathway via switching action modes in rice. We find that miR408-5p usually inhibits IAA30 protein translation, but in a high auxin environment, it promotes the decay of IAA30 mRNA when it is overproduced. We further demonstrate that IDEAL PLANT ARCHITECTURE1 (IPA1), an SPL transcription factor regulated by miR156, mediates leaf inclination through association with miR408-5p precursor promoter. We finally show that the miR156-IPA1-miR408-5p-IAA30 module could be controlled by miR393, which silences auxin receptors. Together, our results define an alternative auxin transduction signaling pathway in rice that involves the switching of function modes by miR408-5p, which contributes to a better understanding of the action machinery as well as the cooperative network of miRNAs in plants.

Effects of Straw Returning and New Fertilizer Substitution on Rice Growth, Yield, and Soil Properties in the Chaohu Lake Region of China

Recently, replacing chemical fertilizers with straw returning and new fertilizers has received considerable attention in the agricultural sector, as it is believed to increase rice yield and improve soil properties. However, less is known about rice growth and soil properties in paddy fields with the addition of different fertilizers. Thus, in this paper, we investigated the effects of different fertilizer treatments, including no fertilization (CK), optimized fertilization based on the medium yield recommended fertilizer amount (OF), 4.50 Mg ha-1 straw returning with chemical fertilizers (SF), 0.59 Mg ha-1 slow-release fertilizer with chemical fertilizers (SRF), and 0.60 Mg ha-1 water-soluble fertilizer with chemical fertilizers (WSF), on rice growth, yield, and soil properties through a field experiment. The results show that compared with the OF treatment, the new SF, SRF, and WSF treatments increased plant height, main root length, tiller number, leaf area index, chlorophyll content, and aboveground dry weight. The SF, SRF, and WSF treatments improved rice grain yield by 30.65-32.51% and 0.24-1.66% compared to the CK and OF treatments, respectively. The SRF treatment increased nitrogen (N) and phosphorus (P) uptake by 18.78% and 28.68%, the harvest indexes of N and P by 1.75% and 0.59%, and the partial productivity of N and P by 2.64% and 2.63%, respectively, compared with the OF treatment. However, fertilization did not significantly affect the average yield, harvest indexes of N and P, and partial productivity of N and P. The contents of TN, AN, SOM, TP, AP, and AK across all the treatments decreased significantly with increasing soil depth, while soil pH increased with soil depth. The SF treatment could more effectively increase soil pH and NH4+-N content compared to the SRF and WSF treatments, while the SRF treatment could greatly enhance other soil nutrients and enzyme activities compared to the SF and WSF treatments. A correlation analysis showed that rice yield was significantly positively associated with tiller number, leaf area index, chlorophyll, soil NO3--N, NH4+-N, SOM, TP, AK, and soil enzyme activity. The experimental results indicate that SRF was the best fertilization method to improve rice growth and yield and enhance soil properties, followed by the SF, WSF, and OF treatments. Hence, the results provide useful information for better fertilization management in the Chaohu Lake region of China.

Potential of rice tillering for sustainable food production

Tillering, also known as shoot branching, is a fundamental trait for cereal crops such as rice to produce sufficient panicle numbers. Effective tillering that guarantees successful panicle production is essential for achieving high crop yields. Recent advances in molecular biology have revealed the mechanisms underlying rice tillering; however, in rice breeding and cultivation, there remain limited genes or alleles suitable for effective tillering and high yields. A recently identified quantitative trait locus (QTL) called MORE PANICLES 3 (MP3) has been cloned as a single gene and shown to promote tillering and to moderately increase panicle number. This gene is an ortholog of the maize domestication gene TB1, and it has the potential to increase grain yield under ongoing climate change and in nutrient-poor environments. This review reconsiders the potential and importance of tillering for sustainable food production. Thus, I provide an overview of rice tiller development and the currently understood molecular mechanisms that underly it, focusing primarily on the biosynthesis and signaling of strigolactones, effective QTLs, and the importance of MP3 (TB1). The possible future benefits in using promising QTLs such as MP3 to explore agronomic solutions under ongoing climate change and in nutrient-poor environments are also highlighted.

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.

Genome-wide identification, evolution, and role of SPL gene family in beet (Beta vulgaris L.) under cold stress

BACKGROUND

SPL transcription factors play vital roles in regulating plant growth, development, and abiotic stress responses. Sugar beet (Beta vulgaris L.), one of the world's main sugar-producing crops, is a major source of edible and industrial sugars for humans. Although the SPL gene family has been extensively identified in other species, no reports on the SPL gene family in sugar beet are available.

RESULTS

Eight BvSPL genes were identified at the whole-genome level and were renamed based on their positions on the chromosome. The gene structure, SBP domain sequences, and phylogenetic relationship with Arabidopsis were analyzed for the sugar beet SPL gene family. The eight BvSPL genes were divided into six groups (II, IV, V, VI, VII, and VIII). Of the BvSPL genes, no tandem duplication events were found, but one pair of segmental duplications was present. Multiple cis-regulatory elements related to growth and development were identified in the 2000-bp region upstream of the BvSPL gene start codon (ATG). Using quantitative real-time polymerase chain reaction (qRT-PCR), the expression profiles of the eight BvSPL genes were examined under eight types of abiotic stress and during the maturation stage. BvSPL transcription factors played a vital role in abiotic stress, with BvSPL3 and BvSPL6 being particularly noteworthy.

CONCLUSION

Eight sugar beet SPL genes were identified at the whole-genome level. Phylogenetic trees, gene structures, gene duplication events, and expression profiles were investigated. The qRT-PCR analysis indicated that BvSPLs play a substantial role in the growth and development of sugar beet, potentially participating in the regulation of root expansion and sugar accumulation.

A mutation in CsDWF7 gene encoding a delta7 sterol C-5(6) desaturase leads to the phenotype of super compact in cucumber (Cucumis sativus L.)

KEY MESSAGE

A novel super compact mutant, scp-3, was identified using map-based cloning in cucumber. The CsDWF7 gene encoding a delta7 sterol C-5(6) desaturase was the candidate gene of scp-3. Mining dwarf genes is important in understanding stem growth in crops. However, only a small number of dwarf genes have been cloned or characterized. Here, we characterized a cucumber (Cucumis sativus L.) dwarf mutant, super compact 3 (scp-3), which displays shortened internodes and dark green leaves with a wrinkled appearance. The photosynthetic rate of scp-3 is significantly lower than that of the wild type. The dwarf phenotype of scp-3 mutant can be partially rescued by the exogenous brassinolide (BL) application, and the endogenous brassinosteroids (BRs) levels in the scp-3 mutant were significantly lower compared to the wild type. Microscopic examination revealed that the reduced internode length in scp-3 resulted from a decrease in cell size. Genetic analysis showed that the dwarf phenotype of scp-3 was controlled by a single recessive gene. Combined with bulked segregant analysis and map-based cloning strategy, we delimited scp-3 locus into an 82.5 kb region harboring five putative genes, but only one non-synonymous mutation (A to T) was discovered between the mutant and its wild type in this region. This mutation occurred within the second exon of the CsGy4G017510 gene, leading to an amino acid alteration from Leu156 to His156. This gene encodes the CsDWF7 protein, an analog of the Arabidopsis DWF7 protein, which is known to be involved in the biosynthesis of BRs. The CsDWF7 protein was targeted to the cell membrane. In comparison to the wild type, scp-3 exhibited reduced CsDWF7 expression in different tissues. These findings imply that CsDWF7 is essential for both BR biosynthesis as well as growth and development of cucumber plants.

Temporal regulation of vegetative phase change in plants

During their vegetative growth, plants reiteratively produce leaves, buds, and internodes at the apical end of the shoot. The identity of these organs changes as the shoot develops. Some traits change gradually, but others change in a coordinated fashion, allowing shoot development to be divided into discrete juvenile and adult phases. The transition between these phases is called vegetative phase change. Historically, vegetative phase change has been studied because it is thought to be associated with an increase in reproductive competence. However, this is not true for all species; indeed, heterochronic variation in the timing of vegetative phase change and flowering has made important contributions to plant evolution. In this review, we describe the molecular mechanism of vegetative phase change, how the timing of this process is controlled by endogenous and environmental factors, and its ecological and evolutionary significance.

Rice PIFs: Critical regulators in rice development and stress response

Phytochrome-interacting factors (PIFs) belong to a subfamily of the basic helix-loop-helix (bHLH) family of transcription factors, which serve as a "hub" for development and growth of plants. They have the capability to regulate the expression of many downstream genes, integrate multiple signaling pathways, and act as a signaling center within the cell. In rice (Oryza sativa), the PIF family genes, known as OsPILs, play a crucial part in many different aspects. OsPILs play a crucial role in regulating various aspects of photomorphogenesis, skotomorphogenesis, plant growth, and development in rice. These vital processes include chlorophyll synthesis, plant gravitropism, plant height, flowering, and response to abiotic stress factors such as low temperature, drought, and high salt. Additionally, OsPILs are involved in controlling several important agronomic traits in rice. Some OsPILs members coordinate with each other to function. This review summarizes and prospects the latest research progress on the biological functions of OsPILs transcription factors and provides a reference for further exploring the functions and mechanism of OsPILs.

Cultivating potential: Harnessing plant stem cells for agricultural crop improvement

Meristems are stem cell-containing structures that produce all plant organs and are therefore important targets for crop improvement. Developmental regulators control the balance and rate of cell divisions within the meristem. Altering these regulators impacts meristem architecture and, as a consequence, plant form. In this review, we discuss genes involved in regulating the shoot apical meristem, inflorescence meristem, axillary meristem, root apical meristem, and vascular cambium in plants. We highlight several examples showing how crop breeders have manipulated developmental regulators to modify meristem growth and alter crop traits such as inflorescence size and branching patterns. Plant transformation techniques are another innovation related to plant meristem research because they make crop genome engineering possible. We discuss recent advances on plant transformation made possible by studying genes controlling meristem development. Finally, we conclude with discussions about how meristem research can contribute to crop improvement in the coming decades.

The cytokinin receptor OHK4/OsHK4 regulates inflorescence architecture in rice via an IDEAL PLANT ARCHITECTURE1/WEALTHY FARMER'S PANICLE-mediated positive feedback circuit

Inflorescence architecture is important for rice (Oryza sativa) grain yield. The phytohormone cytokinin (CK) has been shown to regulate rice inflorescence development; however, the underlying mechanism mediated by CK perception is still unclear. Employing a forward genetic approach, we isolated an inactive variant of the CK receptor OHK4/OsHK4 gene named panicle length1, which shows decreased panicle size due to reduced inflorescence meristem (IM) activity. A 2-amino acid deletion in the long α-helix stalk of the sensory module of OHK4 impairs the homodimerization and ligand-binding capacity of the receptor, even though the residues do not touch the ligand-binding domain or the dimerization interface. This deletion impairs CK signaling that occurs through the type-B response regulator OsRR21, which acts downstream of OHK4 in controlling inflorescence size. Meanwhile, we found that IDEAL PLANT ARCHITECTURE1(IPA1)/WEALTHY FARMER'S PANICLE (WFP), encoding a positive regulator of IM development, acts downstream of CK signaling and is directly activated by OsRR21. Additionally, we revealed that IPA1/WFP directly binds to the OHK4 promoter and upregulates its expression through interactions with 2 TCP transcription factors, forming a positive feedback circuit. Altogether, we identified the OHK4-OsRR21-IPA1 regulatory module, providing important insights into the role of CK signaling in regulating rice inflorescence architecture.

The OsNLP3/4-OsRFL module regulates nitrogen-promoted panicle architecture in rice

Rice panicles, a major component of yield, are regulated by phytohormones and nutrients. How mineral nutrients promote panicle architecture remains largely unknown. Here, we report that NIN-LIKE PROTEIN3 and 4 (OsNLP3/4) are crucial positive regulators of rice panicle architecture in response to nitrogen (N). Loss-of-function mutants of either OsNLP3 or OsNLP4 produced smaller panicles with reduced primary and secondary branches and fewer grains than wild-type, whereas their overexpression plants showed the opposite phenotypes. The OsNLP3/4-regulated panicle architecture was positively correlated with N availability. OsNLP3/4 directly bind to the promoter of OsRFL and activate its expression to promote inflorescence meristem development. Furthermore, OsRFL activates OsMOC1 expression by binding to its promoter. Our findings reveal the novel N-responsive OsNLP3/4-OsRFL-OsMOC1 module that integrates N availability to regulate panicle architecture, shedding light on how N nutrient signals regulate panicle architecture and providing candidate targets for the improvement of crop yield.

Low phosphorus promotes NSP1-NSP2 heterodimerization to enhance strigolactone biosynthesis and regulate shoot and root architecture in rice

Phosphorus is an essential macronutrient for plant development and metabolism, and plants have evolved ingenious mechanisms to overcome phosphate (Pi) starvation. However, the molecular mechanisms underlying the regulation of shoot and root architecture by low phosphorus conditions and the coordinated utilization of Pi and nitrogen remain largely unclear. Here, we show that Nodulation Signaling Pathway 1 (NSP1) and NSP2 regulate rice tiller number by promoting the biosynthesis of strigolactones (SLs), a class of phytohormones with fundamental effects on plant architecture and environmental responses. We found that NSP1 and NSP2 are induced by Oryza sativa PHOSPHATE STARVATION RESPONSE2 (OsPHR2) in response to low-Pi stress and form a complex to directly bind the promoters of SL biosynthesis genes, thus markedly increasing SL biosynthesis in rice. Interestingly, the NSP1/2-SL signaling module represses the expression of CROWN ROOTLESS 1 (CRL1), a newly identified early SL-responsive gene in roots, to restrain lateral root density under Pi deficiency. We also demonstrated that GR244DO treatment under normal conditions inhibits the expression of OsNRTs and OsAMTs to suppress nitrogen absorption but enhances the expression of OsPTs to promote Pi absorption, thus facilitating the balance between nitrogen and phosphorus uptake in rice. Importantly, we found that NSP1p:NSP1 and NSP2p:NSP2 transgenic plants show improved agronomic traits and grain yield under low- and medium-phosphorus conditions. Taken together, these results revealed a novel regulatory mechanism of SL biosynthesis and signaling in response to Pi starvation, providing genetic resources for improving plant architecture and nutrient-use efficiency in low-Pi environments.

OsMDH12: A Peroxisomal Malate Dehydrogenase Regulating Tiller Number and Salt Tolerance in Rice

Salinity is an important environmental factor influencing crop growth and yield. Malate dehydrogenase (MDH) catalyses the reversible conversion of oxaloacetate (OAA) to malate. While many MDHs have been identified in various plants, the biochemical function of MDH in rice remains uncharacterised, and its role in growth and salt stress response is largely unexplored. In this study, the biochemical function of OsMDH12 was determined, revealing its involvement in regulating tiller number and salt tolerance in rice. OsMDH12 localises in the peroxisome and is expressed across various organs. In vitro analysis confirmed that OsMDH12 converts OAA to malate. Seedlings of OsMDH12-overexpressing (OE) plants had shorter shoot lengths and lower fresh weights than wild-type (WT) plants, while osmdh12 mutants displayed the opposite. At maturity, OsMDH12-OE plants had fewer tillers than WT, whereas osmdh12 mutants had more, suggesting OsMDH12's role in tiller number regulation. Moreover, OsMDH12-OE plants were sensitive to salt stress, but osmdh12 mutants showed enhanced salt tolerance. The Na+/K+ content ratio increased in OsMDH12-OE plants and decreased in osmdh12 mutants, suggesting that OsMDH12 might negatively affect salt tolerance through influencing the Na+/K+ balance. These findings hint at OsMDH12's potential as a genetic tool to enhance rice growth and salt tolerance.

OsMADS5 interacts with OsSPL14/17 to inhibit rice root elongation by restricting cell proliferation of root meristem under ammonium supply

Nitrogen (N) is a vital major nutrient for rice (Oryza sativa). Rice responds to different applications of N by altering its root morphology, including root elongation. Although ammonium (NH 4 + ) is the primary source of N for rice,NH 4 + is toxic to rice roots and inhibits root elongation. However, the precise molecular mechanism thatNH 4 + -inhibited root elongation of rice is not well understood. Here, we identified a rice T-DNA insert mutant of OsMADS5 with a longer seminal root (SR) under sufficient N conditions. Reverse-transcription quantitative PCR analysis revealed that the expression level of OsMADS5 was increased underNH 4 + compared withNO 3 - supply. UnderNH 4 + conditions, knocking out OsMADS5 (cas9) produced a longer SR, phenocopying osmads5, while there was no significant difference in SR length between wild-type and cas9 underNO 3 - supply. Moreover, OsMADS5-overexpression plants displayed the opposite SR phenotype. Further study demonstrated that enhancement of OsMADS5 byNH 4 + supply inhibited rice SR elongation, likely by reducing root meristem activity of root tip, with the involvement of OsCYCB1;1. We also found that OsMADS5 interacted with OsSPL14 and OsSPL17 (OsSPL14/17) to repress their transcriptional activation by attenuating DNA binding ability. Moreover, loss of OsSPL14/17 function in osmads5 eliminated its stimulative effect on SR elongation underNH 4 + conditions, implying OsSPL14/17 may function downstream of OsMADS5 to mediate rice SR elongation underNH 4 + supply. Overall, our results indicate the existence of a novel modulatory pathway in which enhancement of OsMADS5 byNH 4 + supply represses the transcriptional activities of OsSPL14/17 to restrict SR elongation of rice.

Inositolphosphorylceramide synthases, OsIPCSs, regulate plant height in rice

Inositolphosphorylceramide synthase (IPCS) catalyses ceramides and phosphatidylinositol (PI) into inositolphosphorylceramide (IPC), which is involved in the regulation of plant growth and development. A total of three OsIPCS family genes have been identified in rice. However, most of their functions remain unknown. Here, the functions of OsIPCSs were analyzed by CRISPR/Cas9 technology, lipidomics analysis, and transcriptomics analysis. Single-gene mutation of OsIPCSs resulted in dwarf phenotype. Among them, the phenotype of osipcs3 mutant was more severe. Multi-gene mutation of OsIPCS genes led to more severe phenotypes, indicating the additive effects of OsIPCSs. We further determined that a significant decrease in epidermal cell elongation of internode in the mutants. There was a significant decrease in the content of IPC detected in the osipcs2/3 and osipcs1/2/3 mutants. The contents of glycosyl inositol phosphoryl ceramide (GIPC) were also decreased by 20% and 10% in osipcs2/3 and osipcs1/2/3, respectively. The results of RNA-seq showed that numerous DEGs found to be associated with cellular component organization, anatomical structure morphogenesis, and cell growth in the osipcs2, osipcs2/3, and osipcs1/2/3. Taken together, OsIPCSs may be involved in the regulation of plant height through affecting cell growth and sphingolipid metabolism in rice.

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.

Bridging pathways: SBP15 regulates GOBLET in modulating tomato axillary bud outgrowth

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Barrera-Rojas CH, Vicente MH, Brito DAP, Silva EM,Muñoz Lopez A, Ferigolo LF, Carmo RM, Silva CMS, Silva GFF, Correa JPO, Notini MM, Freschi L, Cubas P, Nogueira FTS. 2023. Tomato miR156-targeted SlSBP15 represses shoot branching by modulating hormone dynamics and interacting with GOBLET and BRANCHED1b. Journal of Experimental Botany 74, 5124–5139.

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.

Rice miR5504 regulates plant height by affecting cell proliferation and expansion

miRNAs play critical roles in the regulation of plant growth and development by cleaving mRNA or repressing transcription. In our previous study, miR5504 with unknown functions was captured by small RNA sequencing. Here, the function and characters of miR5504 were extensively analyzed using CRISPR/Cas9, overexpression strategy, Northern blot, cytological analysis, and transcriptomics analysis. We found that the dwarf phenotype of mir5504 mutants (mir5504-1 and mir5504-2) appeared on 35-day seedlings and became more apparent at the mature stage. The cytological results showed a substantial decrease in the vascular bundle number, cell number and cell length in the mir5504 mutant compared with NIP. In addition, we found that miR5504 regulated plant height by targeting LOC_Os08g16914. The results of RNA-seq revealed that numerous biological processes were mainly enriched, including DNA-binding transcription factor activity, transferase activity, regulation of transcription, metabolic process, and protein binding. Meanwhile, KEEG analysis showed that numerous proteins were associated with cellular processes and metabolism pathways. Taken together, miR5504 may be involved in the regulation of plant height by affecting cell expansion and division of internode in rice.

CRISPR/Cas Technology Revolutionizes Crop Breeding

Crop breeding is an important global strategy to meet sustainable food demand. CRISPR/Cas is a most promising gene-editing technology for rapid and precise generation of novel germplasm and promoting the development of a series of new breeding techniques, which will certainly lead to the transformation of agricultural innovation. In this review, we summarize recent advances of CRISPR/Cas technology in gene function analyses and the generation of new germplasms with increased yield, improved product quality, and enhanced resistance to biotic and abiotic stress. We highlight their applications and breakthroughs in agriculture, including crop de novo domestication, decoupling the gene pleiotropy tradeoff, crop hybrid seed conventional production, hybrid rice asexual reproduction, and double haploid breeding; the continuous development and application of these technologies will undoubtedly usher in a new era for crop breeding. Moreover, the challenges and development of CRISPR/Cas technology in crops are also discussed.

Linking glucose signaling to nitrogen utilization by the OsHXK7-ARE4 complex in rice

How reciprocal regulation of carbon and nitrogen metabolism works is a long-standing question. In plants, glucose and nitrate are proposed to act as signaling molecules, regulating carbon and nitrogen metabolism via largely unknown mechanisms. Here, we show that the MYB-related transcription factor ARE4 coordinates glucose signaling and nitrogen utilization in rice. ARE4 is retained in the cytosol in complexing with the glucose sensor OsHXK7. Upon sensing a glucose signal, ARE4 is released, is translocated into the nucleus, and activates the expression of a subset of high-affinity nitrate transporter genes, thereby boosting nitrate uptake and accumulation. This regulatory scheme displays a diurnal pattern in response to circadian changes of soluble sugars. The are4 mutations compromise in nitrate utilization and plant growth, whereas overexpression of ARE4 increases grain size. We propose that the OsHXK7-ARE4 complex links glucose to the transcriptional regulation of nitrogen utilization, thereby coordinating carbon and nitrogen metabolism.

Synthetic developmental biology: molecular tools to re-design plant shoots and roots

Plant morphology and anatomy strongly influence agricultural yield. Crop domestication has strived for desirable growth and developmental traits, such as larger and more fruits and semi-dwarf architecture. Genetic engineering has accelerated rational, purpose-driven engineering of plant development, but it can be unpredictable. Developmental pathways are complex and riddled with environmental and hormonal inputs, as well as feedback and feedforward interactions, which occur at specific times and places in a growing multicellular organism. Rational modification of plant development would probably benefit from precision engineering based on synthetic biology approaches. This review outlines recently developed synthetic biology technologies for plant systems and highlights their potential for engineering plant growth and development. Streamlined and high-capacity genetic construction methods (Golden Gate DNA Assembly frameworks and toolkits) allow fast and variation-series cloning of multigene transgene constructs. This, together with a suite of gene regulation tools (e.g. cell type-specific promoters, logic gates, and multiplex regulation systems), is starting to enable developmental pathway engineering with predictable outcomes in model plant and crop species.

Rice microRNA156/529-SQUAMOSA PROMOTER BINDING PROTEIN-LIKE7/14/17 modules regulate defenses against bacteria

Rice (Oryza sativa L.) microRNA156/529-SQUAMOSA PROMOTER BINDING PROTEIN-LIKE7/14/17 (miR156/529-SPL7/14/17) modules have pleiotropic effects on many biological pathways. OsSPL7/14 can interact with DELLA protein SLENDER RICE1 (SLR1) to modulate gibberellin acid (GA) signal transduction against the bacterial pathogen Xanthomonas oryzae pv. oryzae. However, whether the miR156/529-OsSPL7/14/17 modules also regulate resistance against other pathogens is unclear. Notably, OsSPL7/14/17 functioning as transcriptional activators, their target genes, and the corresponding downstream signaling pathways remain largely unexplored. Here, we demonstrate that miR156/529 play negative roles in plant immunity and that miR156/529-regulated OsSPL7/14/17 confer broad-spectrum resistance against 2 devastating bacterial pathogens. Three OsSPL7/14/17 proteins directly bind to the promoters of rice Allene Oxide Synthase 2 (OsAOS2) and NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 (OsNPR1) and activate their transcription, regulating jasmonic acid (JA) accumulation and the salicylic acid (SA) signaling pathway, respectively. Overexpression of OsAOS2 or OsNPR1 impairs the susceptibility of the osspl7/14/17 triple mutant. Exogenous application of JA enhances resistance of the osspl7/14/17 triple mutant and the miR156 overexpressing plants. In addition, genetic evidence confirms that bacterial pathogen-activated miR156/529 negatively regulate pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) responses, such as pattern recognition receptor Xa3/Xa26-initiated PTI. Our findings demonstrate that bacterial pathogens modulate miR156/529-OsSPL7/14/17 modules to suppress OsAOS2-catalyzed JA accumulation and the OsNPR1-promoted SA signaling pathway, facilitating pathogen infection. The uncovered miR156/529-OsSPL7/14/17-OsAOS2/OsNPR1 regulatory network provides a potential strategy to genetically improve rice disease resistance.

RNA-Seq Transcriptome Analysis and Evolution of OsEBS, a Gene Involved in Enhanced Spikelet Number per Panicle in Rice

Spikelet number per panicle (SNP) is one of the most important yield components in rice. Rice ENHANCING BIOMASS AND SPIKELET NUMBER (OsEBS), a gene involved in improved SNP and yield, has been cloned from an accession of Dongxiang wild rice. However, the mechanism of OsEBS increasing rice SNP is poorly understood. In this study, the RNA-Seq technology was used to analyze the transcriptome of wildtype Guichao 2 and OsEBS over-expression line B102 at the heading stage, and analysis of the evolution of OsEBS was also conducted. A total of 5369 differentially expressed genes (DEGs) were identified between Guichao2 and B102, most of which were down-regulated in B102. Analysis of the expression of endogenous hormone-related genes revealed that 63 auxin-related genes were significantly down-regulated in B102. Gene Ontogeny (GO) enrichment analysis showed that the 63 DEGs were mainly enriched in eight GO terms, including auxin-activated signaling pathway, auxin polar transport, auxin transport, basipetal auxin transport, and amino acid transmembrane transport, most of which were directly or indirectly related to polar auxin transport. Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathway analysis further verified that the down-regulated genes related to polar auxin transport had important effects on increased SNP. Analysis of the evolution of OsEBS found that OsEBS was involved in the differentiation of indica and japonica, and the differentiation of OsEBS supported the multi-origin model of rice domestication. Indica (XI) subspecies harbored higher nucleotide diversity than japonica (GJ) subspecies in the OsEBS region, and XI experienced strong balancing selection during evolution, while selection in GJ was neutral. The degree of genetic differentiation between GJ and Bas subspecies was the smallest, while it was the highest between GJ and Aus. Phylogenetic analysis of the Hsp70 family in O. sativa, Brachypodium distachyon, and Arabidopsis thaliana indicated that changes in the sequences of OsEBS were accelerated during evolution. Accelerated evolution and domain loss in OsEBS resulted in neofunctionalization. The results obtained from this study provide an important theoretical basis for high-yield rice breeding.

Fertilization controls tiller numbers via transcriptional regulation of a MAX1-like gene in rice cultivation

Fertilization controls various aspects of cereal growth such as tiller number, leaf size, and panicle size. However, despite such benefits, global chemical fertilizer use must be reduced to achieve sustainable agriculture. Here, based on field transcriptome data from leaf samples collected during rice cultivation, we identify fertilizer responsive genes and focus on Os1900, a gene orthologous to Arabidopsis thaliana MAX1, which is involved in strigolactone biosynthesis. Elaborate genetic and biochemical analyses using CRISPR/Cas9 mutants reveal that Os1900 together with another MAX1-like gene, Os5100, play a critical role in controlling the conversion of carlactone into carlactonoic acid during strigolactone biosynthesis and tillering in rice. Detailed analyses of a series of Os1900 promoter deletion mutations suggest that fertilization controls tiller number in rice through transcriptional regulation of Os1900, and that a few promoter mutations alone can increase tiller numbers and grain yields even under minor-fertilizer conditions, whereas a single defective os1900 mutation does not increase tillers under normal fertilizer condition. Such Os1900 promoter mutations have potential uses in breeding programs for sustainable rice production.

Genetic mapping and functional analysis of a classical tassel branch number mutant Tp2 in maize

Tassel branch number is a key trait that contributes greatly to grain yield in maize (Zea mays). We obtained a classical mutant from maize genetics cooperation stock center, Teopod2 (Tp2), which exhibits severely decreased tassel branch. We conducted a comprehensive study, including phenotypic investigation, genetic mapping, transcriptome analysis, overexpression and CRISPR knock-out, and tsCUT&Tag of Tp2 gene for the molecular dissection of Tp2 mutant. Phenotypic investigation showed that it is a pleiotropic dominant mutant, which is mapped to an interval of approximately 139-kb on Chromosome 10 harboring two genes Zm00001d025786 and zma-miR156h. Transcriptome analysis showed that the relative expression level of zma-miR156h was significantly increased in mutants. Meanwhile, overexpression of zma-miR156h and knockout materials of ZmSBP13 exhibited significantly decreased tassel branch number, a similar phenotype with Tp2 mutant, suggesting that zma-miR156h is the causal gene of Tp2 and targets ZmSBP13 gene. Besides, the potential downstream genes of ZmSBP13 were uncovered and showed that it may target multiple proteins to regulate inflorescence structure. Overall, we characterized and cloned Tp2 mutant, and proposed a zma-miR156h-ZmSBP13 model functioning in regulating tassel branch development in maize, which is an essential measure to satisfy the increasing demands of cereals.

MORE PANICLES 3, a natural allele of OsTB1/FC1, impacts rice yield in paddy fields at elevated CO2 levels

Improving crop yield potential through an enhanced response to rising atmospheric CO₂ levels is an effective strategy for sustainable crop production in the face of climate change. Large-sized panicles (containing many spikelets per panicle) have been a recent ideal plant architecture (IPA) for high-yield rice breeding. However, few breeding programs have proposed an IPA under the projected climate change. Here, we demonstrate through the cloning of the rice (Oryza sativa) quantitative trait locus for MORE PANICLES 3 (MP3) that the improvement in panicle number increases grain yield at elevated atmospheric CO₂ levels. MP3 is a natural allele of OsTB1/FC1, previously reported as a negative regulator of tiller bud outgrowth. The temperate japonica allele advanced the developmental process in axillary buds, moderately promoted tillering, and increased the panicle number without negative effects on the panicle size or culm thickness in a high-yielding indica cultivar with large-sized panicles. The MP3 allele, containing three exonic polymorphisms, was observed in most accessions in the temperate japonica subgroups but was rarely observed in the indica subgroup. No selective sweep at MP3 in either the temperate japonica or indica subgroups suggested that MP3 has not been involved and utilized in artificial selection during domestication or breeding. A free-air CO₂ enrichment experiment revealed a clear increase of grain yield associated with the temperate japonica allele at elevated atmospheric CO₂ levels. Our findings show that the moderately increased panicle number combined with large-sized panicles using MP3 could be a novel IPA and contribute to an increase in rice production under climate change with rising atmospheric CO₂ levels.

Natural variation in Tiller Number 1 affects its interaction with TIF1 to regulate tillering in rice

Tiller number per plant-a cardinal component of ideal plant architecture-affects grain yield potential. Thus, alleles positively affecting tillering must be mined to promote genetic improvement. Here, we report a Tiller Number 1 (TN1) protein harbouring a bromo-adjacent homology domain and RNA recognition motifs, identified through genome-wide association study of tiller numbers. Natural variation in TN1 affects its interaction with TIF1 (TN1 interaction factor 1) to affect DWARF14 expression and negatively regulate tiller number in rice. Further analysis of variations in TN1 among indica genotypes according to geographical distribution revealed that low-tillering varieties with TN1-hap^L are concentrated in Southeast Asia and East Asia, whereas high-tillering varieties with TN1-hap^H are concentrated in South Asia. Taken together, these results indicate that TN1 is a tillering regulatory factor whose alleles present apparent preferential utilization across geographical regions. Our findings advance the molecular understanding of tiller development.

SEMI-ROLLED LEAF 10 stabilizes catalase isozyme B to regulate leaf morphology and thermotolerance in rice (Oryza sativa L.)

Plant architecture and stress tolerance play important roles in rice breeding. Specific leaf morphologies and ideal plant architecture can effectively improve both abiotic stress resistance and rice grain yield. However, the mechanism by which plants simultaneously regulate leaf morphogenesis and stress resistance remains elusive. Here, we report that SRL10, which encodes a double-stranded RNA-binding protein, regulates leaf morphology and thermotolerance in rice through alteration of microRNA biogenesis. The srl10 mutant had a semi-rolled leaf phenotype and elevated sensitivity to high temperature. SRL10 directly interacted with catalase isozyme B (CATB), and the two proteins mutually increased one other's stability to enhance hydrogen peroxide (H₂ O₂ ) scavenging, thereby contributing to thermotolerance. The natural Hap3 (AGC) type of SRL10 allele was found to be present in the majority of aus rice accessions, and was identified as a thermotolerant allele under high temperature stress in both the field and the growth chamber. Moreover, the seed-setting rate was 3.19 times higher and grain yield per plant was 1.68 times higher in near-isogenic line (NIL) carrying Hap3 allele compared to plants carrying Hap1 allele under heat stress. Collectively, these results reveal a new locus of interest and define a novel SRL10-CATB based regulatory mechanism for developing cultivars with high temperature tolerance and stable yield. Furthermore, our findings provide a theoretical basis for simultaneous breeding for plant architecture and stress resistance.

Two florigens and a florigen-like protein form a triple regulatory module at the shoot apical meristem to promote reproductive transitions in rice

Many plant species monitor and respond to changes in day length (photoperiod) for aligning reproduction with a favourable season. Day length is measured in leaves and, when appropriate, leads to the production of floral stimuli called florigens that are transmitted to the shoot apical meristem to initiate inflorescence development¹. Rice possesses two florigens encoded by HEADING DATE 3a (Hd3a) and RICE FLOWERING LOCUS T 1 (RFT1)². Here we show that the arrival of Hd3a and RFT1 at the shoot apical meristem activates FLOWERING LOCUS T-LIKE 1 (FT-L1), encoding a florigen-like protein that shows features partially differentiating it from typical florigens. FT-L1 potentiates the effects of Hd3a and RFT1 during the conversion of the vegetative meristem into an inflorescence meristem and organizes panicle branching by imposing increasing determinacy to distal meristems. A module comprising Hd3a, RFT1 and FT-L1 thus enables the initiation and balanced progression of panicle development towards determinacy.