NARROW LEAF 7 controls leaf shape mediated by auxin in rice

Endogenous cAMP elevation in Brassica napus causes changes in phytohormone levels

In higher plants, the regulatory roles of cAMP (cyclic adenosine 3',5'-monophosphate) signaling remain elusive until now. Cellular cAMP levels are generally much lower in higher plants than in animals and transiently elevated for triggering downstream signaling events. Moreover, plant adenylate cyclase (AC) activities are found in different moonlighting multifunctional proteins, which may pose additional complications in distinguishing a specific signaling role for cAMP. Here, we have developed rapeseed (Brassica napus L.) transgenic plants that overexpress an inducible plant-origin AC activity for generating high AC levels much like that in animal cells, which served the genetic model disturbing native cAMP signaling as a whole in plants. We found that overexpression of the soluble AC activity had significant impacts on the contents of indole-3-acetic acid (IAA) and stress phytohormones, i.e. jasmonic acid (JA), abscisic acid (ABA), and salicylic acid (SA) in the transgenic plants. Acute induction of the AC activity caused IAA overaccumulation, and upregulation of TAA1 and CYP83B1 in the IAA biosynthesis pathways, but also simultaneously the hyper-induction of PR4 and KIN2 expression indicating activation of JA and ABA signaling pathways. We observed typical overgrowth phenotypes related to IAA excess in the transgenic plants, including significant increases in plant height, internode length, width of leaf blade, petiole length, root length, and fresh shoot biomass, as well as the precocious seed development, as compared to wild-type plants. In addition, we identified a set of 1465 cAMP-responsive genes (CRGs), which are most significantly enriched in plant hormone signal transduction pathway, and function mainly in relevance to hormonal, abiotic and biotic stress responses, as well as growth and development. Collectively, our results support that cAMP elevation impacts phytohormone homeostasis and signaling, and modulates plant growth and development. We proposed that cAMP signaling may be critical in configuring the coordinated regulation of growth and development in higher plants.

GHCU, a Molecular Chaperone, Regulates Leaf Curling by Modulating the Distribution of KNGH1 in Cotton

Leaf shape is considered to be one of the most significant agronomic traits in crop breeding. However, the molecular basis underlying leaf morphogenesis in cotton is still largely unknown. In this study, through genetic mapping and molecular investigation using a natural cotton mutant cu with leaves curling upward, the causal gene GHCU is successfully identified as the key regulator of leaf flattening. Knockout of GHCU or its homolog in cotton and tobacco using CRISPR results in abnormal leaf shape. It is further discovered that GHCU facilitates the transport of the HD protein KNOTTED1-like (KNGH1) from the adaxial to the abaxial domain. Loss of GHCU function restricts KNGH1 to the adaxial epidermal region, leading to lower auxin response levels in the adaxial boundary compared to the abaxial. This spatial asymmetry in auxin distribution produces the upward-curled leaf phenotype of the cu mutant. By analysis of single-cell RNA sequencing and spatiotemporal transcriptomic data, auxin biosynthesis genes are confirmed to be expressed asymmetrically in the adaxial-abaxial epidermal cells. Overall, these findings suggest that GHCU plays a crucial role in the regulation of leaf flattening through facilitating cell-to-cell trafficking of KNGH1 and hence influencing the auxin response level.

CsRAXs negatively regulate leaf size and fruiting ability through auxin glycosylation in cucumber

Leaves are the main photosynthesis organ that directly determines crop yield and biomass. Dissecting the regulatory mechanism of leaf development is crucial for food security and ecosystem turn-over. Here, we identified the novel function of R2R3-MYB transcription factors CsRAXs in regulating cucumber leaf size and fruiting ability. Csrax5 single mutant exhibited enlarged leaf size and stem diameter, and Csrax1/2/5 triple mutant displayed further enlargement phenotype. Overexpression of CsRAX1 or CsRAX5 gave rise to smaller leaf and thinner stem. The fruiting ability of Csrax1/2/5 plants was significantly enhanced, while that of CsRAX5 overexpression lines was greatly weakened. Similarly, cell number and free auxin level were elevated in mutant plants while decreased in overexpression lines. Biochemical data indicated that CsRAX1/5 directly promoted the expression of auxin glucosyltransferase gene CsUGT74E2. Therefore, our data suggested that CsRAXs function as repressors for leaf size development by promoting auxin glycosylation to decrease free auxin level and cell division in cucumber. Our findings provide new gene targets for cucumber breeding with increased leaf size and crop yield.

Advancements in Rice Leaf Development Research

Rice leaf morphology is a pivotal component of the ideal plant architecture, significantly impacting rice yield. The process of leaf development unfolds through three distinct stages: the initiation of leaf primordia, the establishment and maintenance of polarity, and leaf expansion. Genes regulating leaf morphology encompass transcription factors, hormones, and miRNAs. An in-depth synthesis and categorization of genes associated with leaf development, particularly those successfully cloned, hold paramount importance in unraveling the complexity of rice leaf development. Furthermore, it provides valuable insights into the potential for molecular-level manipulation of rice leaf types. This comprehensive review consolidates the stages of rice leaf development, the genes involved, molecular regulatory pathways, and the influence of plant hormones. Its objective is to establish a foundational understanding of the creation of ideal rice leaf forms and their practical application in molecular breeding.

DNAL7, a new allele of NAL11, has major pleiotropic effects on rice architecture

MAIN CONCLUSION

dnal7, a novel allelic variant of the OsHSP40, affects rice plant architecture and grain yield by coordinating auxins, cytokinins, and gibberellic acids. Plant height and leaf morphology are the most important traits of the ideal plant architecture (IPA), and discovering related genes is critical for breeding high-yield rice. Here, a dwarf and narrow leaf 7 (dnal7) mutant was identified from a γ-ray treated mutant population, which exhibits pleiotropic effects, including dwarfing, narrow leaves, small seeds, and low grain yield per plant compared to the wild type (WT). Histological analysis showed that the number of veins and the distance between adjacent small veins (SVs) were significantly reduced compared to the WT, indicating that DNAL7 controls leaf size by regulating the formation of veins. Map-based cloning and transgenic complementation revealed that DNAL7 is allelic to NAL11, which encodes OsHSP40, and the deletion of 2 codons in dnal7 destroyed the His-Pro-Asp (HPD) motif of OsHSP40. In addition, expression of DNAL7 in both WT and dnal7 gradually increased with the increase of temperature in the range of 27-31 °C. Heat stress significantly affected the seedling height and leaf width of the dnal7 mutant. A comparative transcriptome analysis of WT and dnal7 revealed that DNAL7 influenced multiple metabolic pathways, including plant hormone signal transduction, carbon metabolism, and biosynthesis of amino acids. Furthermore, the contents of the cytokinins in leaf blades were much higher in dnal7 than in the WT, whereas the contents of auxins were lower in dnal7. The contents of bioactive gibberellic acids (GAs) including GA1, GA3, and GA4 in shoots were decreased in dnal7. Thus, DNAL7 regulates rice plant architecture by coordinating the balance of auxins, cytokinins, and GAs. These results indicate that OsHSP40 is a pleiotropic gene, which plays an important role in improving rice yield and plant architecture.

A guide to barley mutants

BACKGROUND

Mutants have had a fundamental impact upon scientific and applied genetics. They have paved the way for the molecular and genomic era, and most of today's crop plants are derived from breeding programs involving mutagenic treatments.

RESULTS

Barley (Hordeum vulgare L.) is one of the most widely grown cereals in the world and has a long history as a crop plant. Barley breeding started more than 100 years ago and large breeding programs have collected and generated a wide range of natural and induced mutants, which often were deposited in genebanks around the world. In recent years, an increased interest in genetic diversity has brought many historic mutants into focus because the collections are regarded as valuable resources for understanding the genetic control of barley biology and barley breeding. The increased interest has been fueled also by recent advances in genomic research, which provided new tools and possibilities to analyze and reveal the genetic diversity of mutant collections.

CONCLUSION

Since detailed knowledge about phenotypic characters of the mutants is the key to success of genetic and genomic studies, we here provide a comprehensive description of mostly morphological barley mutants. The review is closely linked to the International Database for Barley Genes and Barley Genetic Stocks ( bgs.nordgen.org ) where further details and additional images of each mutant described in this review can be found.

Identification and Transcriptome Analysis of a Novel Allelic Mutant of NAL1 in Rice

Leaf morphology is a crucial aspect of plant architecture, yet the molecular mechanisms underlying leaf development remain incompletely understood. In this study, a narrow leaf mutant, m625, was identified in rice (Oryza sativa L.), exhibiting pleiotropic developmental defects. Pigment measurement revealed reduced levels of photochromic pigments in m625. Cytological analysis demonstrated that the m625 gene affected vascular patterns and cell division. Specifically, the narrowing of the leaf was attributed to a decrease in small vein number, shorter vein spacing, and an abnormal V-shaped arrangement of bulliform cells, while the thickening was caused by longer leaf veins, thicker mesophyll cells, and an increased number of parenchyma cell layers. The dwarf stature and thickened internode were primarily due to shortened internodes and an increase in cell layers, respectively. Positional cloning and complementation assays indicated that the m625 gene is a novel allele of NAL1. In the m625 mutant, a nucleotide deletion at position 1103 in the coding sequence of NAL1 led to premature termination of protein translation. Further RNA-Seq and qRT-PCR analyses revealed that the m625 gene significantly impacted regulatory pathways related to IAA and ABA signal transduction, photosynthesis, and lignin biosynthesis. Moreover, the m625 mutant displayed thinner sclerenchyma and cell walls in both the leaf and stem, particularly showing reduced lignified cell walls in the midrib of the leaf. In conclusion, our study suggests that NAL1, in addition to its known roles in IAA transport and leaf photosynthesis, may also participate in ABA signal transduction, as well as regulate secondary cell wall formation and sclerenchyma thickness through lignification.

Genetics and metabolic responses of Artemisia annua L to the lake of phosphorus under the sparingly soluble phosphorus fertilizer: evidence from transcriptomics analysis

The medicinal herb Artemisia annua L. is prized for its capacity to generate artemisinin, which is used to cure malaria. Potentially influencing the biomass and secondary metabolite synthesis of A. annua is plant nutrition, particularly phosphorus (P). However, most soil P exist as insoluble inorganic and organic phosphates, which results to low P availability limiting plant growth and development. Although plants have developed several adaptation strategies to low P levels, genetics and metabolic responses to P status remain largely unknown. In a controlled greenhouse experiment, the sparingly soluble P form, hydroxyapatite (Ca5OH(PO4)3/CaP) was used to simulate calcareous soils with low P availability. In contrast, the soluble P form KH2PO4/KP was used as a control. A. annua's morphological traits, growth, and artemisinin concentration were determined, and RNA sequencing was used to identify the differentially expressed genes (DEGs) under two different P forms. Total biomass, plant height, leaf number, and stem diameter, as well as leaf area, decreased by 64.83%, 27.49%, 30.47%, 38.70%, and 54.64% in CaP compared to KP; however, LC-MS tests showed an outstanding 37.97% rise in artemisinin content per unit biomass in CaP contrary to KP. Transcriptome analysis showed 2015 DEGs (1084 up-regulated and 931 down-regulated) between two P forms, including 39 transcription factor (TF) families. Further analysis showed that DEGs were mainly enriched in carbohydrate metabolism, secondary metabolites biosynthesis, enzyme catalytic activity, signal transduction, and so on, such as tricarboxylic acid (TCA) cycle, glycolysis, starch and sucrose metabolism, flavonoid biosynthesis, P metabolism, and plant hormone signal transduction. Meanwhile, several artemisinin biosynthesis genes were up-regulated, including DXS, GPPS, GGPS, MVD, and ALDH, potentially increasing artemisinin accumulation. Furthermore, 21 TF families, including WRKY, MYB, bHLH, and ERF, were up-regulated in reaction to CaP, confirming their importance in P absorption, internal P cycling, and artemisinin biosynthesis regulation. Our results will enable us to comprehend how low P availability impacts the parallel transcriptional control of plant development, growth, and artemisinin production in A. annua. This study could lay the groundwork for future research into the molecular mechanisms underlying A. annua's low P adaptation.

Auxins and grass shoot architecture: how the most important hormone makes the most important plants

Cereals are a group of grasses cultivated by humans for their grain. It is from these cereal grains that the majority of all calories consumed by humans are derived. The production of these grains is the result of the development of a series of hierarchical reproductive structures that form the distinct shoot architecture of the grasses. Being spatiotemporally complex, the coordination of grass shoot development is tightly controlled by a network of genes and signals, including the key phytohormone auxin. Hormonal manipulation has therefore been identified as a promising potential approach to increasing cereal crop yields and therefore ultimately global food security. Recent work translating the substantial body of auxin research from model plants into cereal crop species is revealing the contribution of auxin biosynthesis, transport, and signalling to the development of grass shoot architecture. This review discusses this still-maturing knowledge base and examines the possibility that changes in auxin biology could have been a causative agent in the evolution of differences in shoot architecture between key grass species, or could underpin the future selective breeding of cereal crops.

SMALL PLANT AND ORGAN 1 (SPO1) Encoding a Cellulose Synthase-like Protein D4 (OsCSLD4) Is an Important Regulator for Plant Architecture and Organ Size in Rice

Plant architecture and organ size are considered as important traits in crop breeding and germplasm improvement. Although several factors affecting plant architecture and organ size have been identified in rice, the genetic and regulatory mechanisms remain to be elucidated. Here, we identified and characterized the small plant and organ 1 (spo1) mutant in rice (Oryza sativa), which exhibits narrow and rolled leaf, reductions in plant height, root length, and grain width, and other morphological defects. Map-based cloning revealed that SPO1 is allelic with OsCSLD4, a gene encoding the cellulose synthase-like protein D4, and is highly expressed in the roots at the seedling and tillering stages. Microscopic observation revealed the spo1 mutant had reduced number and width in leaf veins, smaller size of leaf bulliform cells, reduced cell length and cell area in the culm, and decreased width of epidermal cells in the outer glume of the grain. These results indicate the role of SPO1 in modulating cell division and cell expansion, which modulates plant architecture and organ size. It is showed that the contents of endogenous hormones including auxin, abscisic acid, gibberellin, and zeatin tested in the spo1 mutant were significantly altered, compared to the wild type. Furthermore, the transcriptome analysis revealed that the differentially expressed genes (DEGs) are significantly enriched in the pathways associated with plant hormone signal transduction, cell cycle progression, and cell wall formation. These results indicated that the loss of SPO1/OsCSLD4 function disrupted cell wall cellulose synthase and hormones homeostasis and signaling, thus leading to smaller plant and organ size in spo1. Taken together, we suggest the functional role of SPO1/OsCSLD4 in the control of rice plant and organ size by modulating cell division and expansion, likely through the effects of multiple hormonal pathways on cell wall formation.

The SlARF4-SlHB8 regulatory module mediates leaf rolling in tomato

Leaf is the main photosynthetic organ in plants and the primary energy source all along the plant life. Given the beneficial role of leaf rolling in improving photosynthetic efficiency and yield in specific environmental conditions, a better understanding of the factors and molecular mechanisms underlying this process is highly suited. Previously, the SlARF4 knocking out mutant exhibited upward curly leaf showed higher resistance to water deficit which driving us to uncover the function of SlARF4 in regulating the curly leaf formation. In this study, we unraveled the unexplored role of the SlARF4-SlHB8 module of transcription factors in the development of leaf rolling. Both SlARF4 loss-of-function and SlHB8 overexpressing tomato plants exhibited upward-rolled leaves, reflecting the active role of the two genes in controlling leaf rolling. Dual-luciferase reporter assays and phenotypic analysis of hybrid progenies suggested that SlHB8 acts downstream of SlARF4 in curly leaf formation. SlARF4 and SlHB8 influence the development of leaf palisade tissues via modulating the expression of genes associated with curly leaf formation. SEM analysis revealed no significant differences in leaf epidermal cells between the two leaf-rolling mutants and the wild type, indicating that curly leaves of arf4 and SlHB8-OE do not result from the asymmetric leaf epidermal cell growth. Our data provide novel insight into the molecular mechanism of abaxial-adaxial determination involving SlARF4 and SlHB8 and reveals that leaf rolling operates via different regulation mechanisms in tomato and Arabidopsis model plant.

NLG1, encoding a mitochondrial membrane protein, controls leaf and grain development in rice

BACKGROUND

Mitochondrion is the key respiratory organ and participate in multiple anabolism and catabolism pathways in eukaryote. However, the underlying mechanism of how mitochondrial membrane proteins regulate leaf and grain development remains to be further elucidated.

RESULTS

Here, a mitochondria-defective mutant narrow leaf and slender grain 1 (nlg1) was identified from an EMS-treated mutant population, which exhibits narrow leaves and slender grains. Moreover, nlg1 also presents abnormal mitochondria structure and was sensitive to the inhibitors of mitochondrial electron transport chain. Map-based cloning and transgenic functional confirmation revealed that NLG1 encodes a mitochondrial import inner membrane translocase containing a subunit Tim21. GUS staining assay and RT-qPCR suggested that NLG1 was mainly expressed in leaves and panicles. The expression level of respiratory function and auxin response related genes were significantly down-regulated in nlg1, which may be responsible for the declination of ATP production and auxin content.

CONCLUSIONS

These results suggested that NLG1 plays an important role in the regulation of leaf and grain size development by maintaining mitochondrial homeostasis. Our finding provides a novel insight into the effects of mitochondria development on leaf and grain morphogenesis in rice.

Auxin biosynthesis gene FveYUC4 is critical for leaf and flower morphogenesis in woodland strawberry

Auxin plays an essential role in plant growth and development, particularly in fruit development. The YUCCA (YUC) genes encode flavin monooxygenases that catalyze a rate-limiting step in auxin biosynthesis. Mutations that disrupt YUC gene function provide useful tools for dissecting general and specific functions of auxin during plant development. In woodland strawberry (Fragaria vesca), two ethyl methanesulfonate mutants, Y422 and Y1011, have been identified that exhibit severe defects in leaves and flowers. In particular, the width of the leaf blade is greatly reduced, and each leaflet in the mutants has fewer and deeper serrations. In addition, the number and shape of the floral organs are altered, resulting in smaller fruits. Mapping by sequencing revealed that both mutations reside in the FveYUC4 gene, and were therefore renamed as yuc4-1 and yuc4-2. Consistent with a role for FveYUC4 in auxin synthesis, free auxin and its metabolites are significantly reduced in the yuc4 leaves and flowers. This role of FveYUC4 in leaf and flower development is supported by its high and specific expression in young leaves and flower buds using GUS reporters. Furthermore, germline transformation of pYUC4::YUC4, which resulted in elevated expression of FveYUC4 in yuc4 mutants, not only rescued the leaf and flower defects but also produced parthenocarpic fruits. Taken together, our data demonstrate that FveYUC4 is essential for leaf and flower morphogenesis in woodland strawberry by providing auxin hormone at the proper time and in the right tissues.

Genetic Analysis for the Flag Leaf Heterosis of a Super-Hybrid Rice WFYT025 Combination Using RNA-Seq

The photosynthetic capacity of flag leaf plays a key role in grain yield in rice. Nevertheless, there are few studies on the heterosis of the rice flag leaf. Therefore, this study focuses on investigating the genetic basis of heterosis for flag leaf in the indica super hybrid rice combination WFYT025 in China using a high-throughput next-generation RNA-seq strategy. We analyzed the gene expression of flag leaf in different environments and different time periods between WFYT025 and its female parent. After obtaining the gene expression profile of the flag leaf, we further investigated the gene regulatory network. Weighted gene expression network analysis (WGCNA) was used to identify the co-expressed gene sets, and a total of 5000 highly expressed genes were divided into 24 co-expression groups. In CHT025, we found 13 WRKY family transcription factors in SDG_hps under the environment of early rice and 16 WRKY family genes in SDG_hps of under the environment of middle rice. We found nine identical transcription factors in the two stages. Except for five reported TFs, the other four TFs might play an important role in heterosis for grain number and photosynthesis. Transcription factors such as WRKY3, WRKY68, and WRKY77 were found in both environments. To eliminate the influence of the environment, we examined the metabolic pathway with the same SDG_hp (SSDG_hp) in two environments. There were 312 SSDG_hps in total. These SSDG_hps mainly focused on the phosphorus metallic process, phosphorylation, plasma membrane, etc. These results provide resources for studying heterosis during super hybrid rice flag leaf development.

Narrow and Stripe Leaf 2 Regulates Leaf Width by Modulating Cell Cycle Progression in Rice

BACKGROUND

Leaf morphology is an important component of the idea plant architecture that extensively influences photosynthesis, transpiration, and ultimately grain yield in crops. However, the genetic and molecular mechanisms regulating this morphology remain largely unclear.

RESULTS

In this study, a mutant showing a narrow and stripe leaf phonotype, designated nsl2, was obtained. Histological analysis revealed defects in the vascular system and reduced epidermal cell number in the nsl2, while the cell size remained unchanged. Map-based cloning and genetic complementation experiments revealed that NSL2, which encodes a small subunit of ribonucleotide reductases (RNRs), is a null allelic with ST1 and SDL. The NSL2 was expressed in variety of tissues, with the highest levels detected in leaves, and its protein was localized in the nucleus and cytoplasm. The dNTPs level was altered in the nsl2 mutant, and thereby affecting the dNTPs pool balance. In addition, flow cytometric analysis and the altered transcript level of genes related to cell cycle indicated that NSL2 affects cell cycle progression.

CONCLUSIONS

Our findings here suggest that NSL2 function in the synthesis of dNTP, the deficient of which leads to DNA synthesis block and in turn affects cell cycle progression, and ultimately decreased cell number and narrow leaf in the nsl2 plant.

Abscisic acid promotes auxin biosynthesis to inhibit primary root elongation in rice

Soil compaction is a global problem causing inadequate rooting and poor yield in crops. Accumulating evidence indicates that phytohormones coordinately regulate root growth via regulating specific growth processes in distinct tissues. However, how abscisic acid (ABA) signaling translates into auxin production to control root growth during adaptation to different soil environments is still unclear. In this study, we report that ABA has biphasic effects on primary root growth in rice (Oryza sativa) through an auxin biosynthesis-mediated process, causing suppression of root elongation and promotion of root swelling in response to soil compaction. We found that ABA treatment induced the expression of auxin biosynthesis genes and auxin accumulation in roots. Conversely, blocking auxin biosynthesis reduced ABA sensitivity in roots, showing longer and thinner primary roots with larger root meristem size and smaller root diameter. Further investigation revealed that the transcription factor basic region and leucine zipper 46 (OsbZIP46), involved in ABA signaling, can directly bind to the YUCCA8/rice ethylene-insensitive 7 (OsYUC8/REIN7) promoter to activate its expression, and genetic analysis revealed that OsYUC8/REIN7 is located downstream of OsbZIP46. Moreover, roots of mutants defective in ABA or auxin biosynthesis displayed the enhanced ability to penetrate compacted soil. Thus, our results disclose the mechanism in which ABA employs auxin as a downstream signal to modify root elongation and radial expansion, resulting in short and swollen roots impaired in their ability to penetrate compacted soil. These findings provide avenues for breeders to select crops resilient to soil compaction.

Longer epidermal cells underlie a quantitative source of variation in wheat flag leaf size

The wheat flag leaf is the main contributor of photosynthetic assimilates to developing grains. Understanding how canopy architecture strategies affect source strength and yield will aid improved crop design. We used an eight-founder population to investigate the genetic architecture of flag leaf area, length, width and angle in European wheat. For the strongest genetic locus identified, we subsequently created a near-isogenic line (NIL) pair for more detailed investigation across seven test environments. Genetic control of traits investigated was highly polygenic, with colocalisation of replicated quantitative trait loci (QTL) for one or more traits identifying 24 loci. For QTL QFll.niab-5A.1 (FLL5A), development of a NIL pair found the FLL5A+ allele commonly conferred a c. 7% increase in flag and second leaf length and a more erect leaf angle, resulting in higher flag and/or second leaf area. Increased FLL5A-mediated flag leaf length was associated with: (1) longer pavement cells and (2) larger stomata at lower density, with a trend for decreased maximum stomatal conductance (G_smax ) per unit leaf area. For FLL5A, cell size rather than number predominantly determined leaf length. The observed trade-offs between leaf size and stomatal morphology highlight the need for future studies to consider these traits at the whole-leaf level.

Genome-Wide Identification, Expression Analysis, and Potential Roles under Abiotic Stress of the YUCCA Gene Family in Mungbean (Vigna radiata L.)

YUCCA, belonging to the class B flavin-dependent monooxygenases, catalyzes the rate-limiting step for endogenous auxin synthesis and is implicated in plant-growth regulation and stress response. Systematic analysis of the YUCCA gene family and its stress response benefits the dissection of regulation mechanisms and breeding applications. In this study, 12 YUCCA genes were identified from the mungbean (Vigna radiata L.) genome and were named based on their similarity to AtYUCCAs. Phylogenetic analysis revealed that the 12 VrYUCCAs could be divided into 4 subfamilies. The evidence from enzymatic assays in vitro and transgenetic Arabidopsis in vivo indicated that all the isolated VrYUCCAs had biological activity in response to IAA synthesis. Expression pattern analysis showed that functional redundancy and divergence existed in the VrYUCCA gene family. Four VrYUCCAs were expressed in most tissues, and five VrYUCCAs were specifically highly expressed in the floral organs. The response toward five stresses, namely, auxin (indole-3-acetic acid, IAA), salinity, drought, high temperatures, and cold, was also investigated here. Five VrYUCCAs responded to IAA in the root, while only VrYUCCA8a was induced in the leaf. VrYUCCA2a, VrYUCCA6a, VrYUCCA8a, VrYUCCA8b, and VrYUCCA10 seemed to dominate under abiotic stresses, due to their sensitivity to the other four treatments. However, the response modes of the VrYUCCAs varied, indicating that they may regulate different stresses in distinct ways to finely adjust IAA content. The comprehensive analysis of the VrYUCCAs in this study lays a solid foundation for further investigation of VrYUCCA genes' mechanisms and applications in breeding.

Multi-model genome-wide association studies of leaf anatomical traits and vein architecture in rice

Introduction

The anatomy of rice leaves is closely related to photosynthesis and grain yield. Therefore, exploring insight into the quantitative trait loci (QTLs) and alleles related to rice flag leaf anatomical and vein traits is vital for rice improvement.

Methods

Here, we aimed to explore the genetic architecture of eight flag leaf traits using one single-locus model; mixed-linear model (MLM), and two multi-locus models; fixed and random model circulating probability unification (FarmCPU) and Bayesian information and linkage disequilibrium iteratively nested keyway (BLINK). We performed multi-model GWAS using 329 rice accessions of RDP1 with 700K single-nucleotide polymorphisms (SNPs) markers.

Results

The phenotypic correlation results indicated that rice flag leaf thickness was strongly correlated with leaf mesophyll cells layer (ML) and thickness of both major and minor veins. All three models were able to identify several significant loci associated with the traits. MLM identified three non-synonymous SNPs near NARROW LEAF 1 (NAL1) in association with ML and the distance between minor veins (IVD) traits.

Discussion

Several numbers of significant SNPs associated with known gene function in leaf development and yield traits were detected by multi-model GWAS performed in this study. Our findings indicate that flag leaf traits could be improved via molecular breeding and can be one of the targets in high-yield rice development.

Understanding the molecular mechanism of leaf morphogenesis in vegetable crops conduces to breeding process

Leaf morphology can affect the development and yield of plants by regulating plant architecture and photosynthesis. Several factors can determine the final leaf morphology, including the leaf complexity, size, shape, and margin type, which suggests that leaf morphogenesis is a complex regulation network. The formation of diverse leaf morphology is precisely controlled by gene regulation on translation and transcription levels. To further reveal this, more and more genome data has been published for different kinds of vegetable crops and advanced genotyping approaches have also been applied to identify the causal genes for the target traits. Therefore, the studies on the molecular regulation of leaf morphogenesis in vegetable crops have also been largely improved. This review will summarize the progress on identified genes or regulatory mechanisms of leaf morphogenesis and development in vegetable crops. These identified markers can be applied for further molecular-assisted selection (MAS) in vegetable crops. Overall, the review will contribute to understanding the leaf morphology of different crops from the perspective of molecular regulation and shortening the breeding cycle for vegetable crops.

Leaf rolling in bread wheat (Triticum aestivum L.) is controlled by the upregulation of a pair of closely linked/duplicate zinc finger homeodomain class transcription factors during moisture stress conditions

Zinc finger-homeodomain (ZF-HDs) class IV transcriptional factors (TFs) is a plant-specific transcription factor and play a key role in stress responses, plant growth, development, and hormonal signaling. In this study, two new leaf rolling TFs genes, namely TaZHD1 and TaZHD10, were identified in wheat using comparative genomic analysis of the target region that carried a major QTL for leaf rolling identified through multi-environment phenotyping and high throughput genotyping of a RIL population. Structural and functional annotation of the candidate ZHD genes with its closest rice orthologs reflects the species-specific evolution and, undoubtedly, validates the notions of remote-distance homology concept. Meanwhile, the morphological analysis resulted in contrasting difference for leaf rolling in extreme RILs between parental lines HD2012 and NI5439 at booting and heading stages. Transcriptome-wide expression profiling revealed that TaZHD10 transcripts showed significantly higher expression levels than TaZHD1 in all leaf tissues upon drought stress. The relative expression of these genes was further validated by qRT-PCR analysis, which also showed consistent results across the studied genotypes at the booting and anthesis stage. The contrasting modulation of these genes under drought conditions and the available evidenced for its epigenetic behavior that might involve the regulation of metabolic and gene regulatory networks. Prediction of miRNAs resulted in five Tae-miRs that could be associated with RNAi mediated control of TaZHD1 and TaZHD10 putatively involved in the metabolic pathway controlling rolled leaf phenotype. Gene interaction network analysis indicated that TaZHD1 and TaZHD10 showed pleiotropic effects and might also involve other functions in wheat in addition to leaf rolling. Overall, the results increase our understanding of TaZHD genes and provide valuable information as robust candidate genes for future functional genomics research aiming for the breeding of wheat varieties tolerant to leaf rolling.

The APC/CTAD1-WIDE LEAF 1-NARROW LEAF 1 pathway controls leaf width in rice

Leaf morphology is one of the most important features of the ideal plant architecture. However, the genetic and molecular mechanisms controlling this feature in crops remain largely unknown. Here, we characterized the rice (Oryza sativa) wide leaf 1 (wl1) mutant, which has wider leaves than the wild-type due to more vascular bundles and greater distance between small vascular bundles. WL1 encodes a Cys-2/His-2-type zinc finger protein that interacts with Tillering and Dwarf 1 (TAD1), a co-activator of the anaphase-promoting complex/cyclosome (APC/C) (a multi-subunit E3 ligase). The APC/CTAD1 complex degrades WL1 via the ubiquitin-26S proteasome degradation pathway. Loss-of-function of TAD1 resulted in plants with narrow leaves due to reduced vascular bundle numbers and distance between the small vascular bundles. Interestingly, we found that WL1 negatively regulated the expression of a narrow leaf gene, NARROW LEAF 1 (NAL1), by recruiting the co-repressor TOPLESS-RELATED PROTEIN and directly binding to the NAL1 regulatory region to inhibit its expression by reducing the chromatin histone acetylation. Furthermore, biochemical and genetic analyses revealed that TAD1, WL1, and NAL1 operated in a common pathway to control the leaf width. Our study establishes an important framework for understanding the APC/CTAD1-WL1-NAL1 pathway-mediated control of leaf width in rice, and provides insights for improving crop plant architecture.

Genome-wide meta-analysis of QTL for morphological related traits of flag leaf in bread wheat

Flag leaf is an important organ for photosynthesis of wheat plants, and a key factor affecting wheat yield. In this study, quantitative trait loci (QTL) for flag leaf morphological traits in wheat reported since 2010 were collected to investigate the genetic mechanism of these traits. Integration of 304 QTLs from various mapping populations into a high-density consensus map composed of various types of molecular markers as well as QTL meta-analysis discovered 55 meta-QTLs (MQTL) controlling morphological traits of flag leaves, of which 10 MQTLs were confirmed by GWAS. Four high-confidence MQTLs (MQTL-1, MQTL-11, MQTL-13, and MQTL-52) were screened out from 55 MQTLs, with an average confidence interval of 0.82 cM and a physical distance of 9.4 Mb, according to the definition of hcMQTL. Ten wheat orthologs from rice (7) and Arabidopsis (3) that regulated leaf angle, development and morphogenesis traits were identified in the hcMQTL region using comparative genomics, and were speculated to be potential candidate genes regulating flag leaf morphological traits in wheat. The results from this study provides valuable information for fine mapping and molecular markers assisted selection to improve morphological characters in wheat flag leaf.

A transcription factor TaMYB5 modulates leaf rolling in wheat

Leaf rolling is an important agronomic trait in wheat (Triticum aestivum L.). Moderate leaf rolling keeps leaves upright and maintains the relatively normal photosynthesis of plants under drought stress. However, the molecular mechanism of wheat leaf rolling remains unclear. Here, we identified a candidate gene TaMYB5-3A that regulates leaf rolling by using a genome-wide association study (GWAS) in a panel of 323 wheat accessions. Phenotype analysis indicated that the leaves of tamyb5 mutants were flatter than that of the wild type under drought condition. A nucleotide variation in the TaMYB5-3A coding region resulted in a substitution of Thr to Lys, which corresponds to two alleles SNP-3A-1 and SNP-3A-2. The leaf rolling index (LRI) of the SNP-3A-1 genotype was significantly lower than that of the SNP-3A-2 genotype. In addition, TaMYB5-3A alleles were associated with canopy temperature (CT) in multiple environments. The CT of the SNP-3A-1 genotype was lower than that of the SNP-3A-2 genotype. Gene expression analysis showed that TaMYB5-3A was mainly expressed in leaves and down-regulated by PEG and ABA treatment. TaMYB5 induces TaNRL1 gene expression through the direct binding to the AC cis-acting element of the promoter of the target gene, which was validated by EMSA (electrophoretic mobility shift assay). Our results revealed a crucial molecular mechanism in wheat leaf rolling and provided the theoretical basis and a gene resource for crop breeding.

Fine mapping of QFlw-5B, a major QTL for flag leaf width in common wheat (Triticum aestivum L.)

A major stable QTL for flag leaf width was narrowed down to 2.5 Mb region containing two predicated putative candidate genes, and its effects on yield-related traits was characterized. Flag leaf width (FLW) is important to production in wheat. In a previous study, a major quantitative trait locus for FLW (QFlw-5B) was detected on chromosome 5B, within an interval of 6.5 cM flanked by the markers of XwPt-9103 and Xbarc142, using a mapping population of recombinant inbred lines derived from a cross between Kenong9204 (KN9204) and Jing411 (J411) (denoted as KJ-RILs). The aim of this study was to fine map QFlw-5B and characterize its genetic effects on yield-related traits. Multiple near-isogenic lines (NILs) were developed using one residual heterozygous line for QFlw-5B. Five recombinants for QFlw-5B were identified, and its location was narrowed to a 2.5 Mb region based on combined phenotypic and genotypic data analysis. This region contained 27 predicted genes, two of which were considered as the most likely candidate genes for QFlw-5B. The FLW of NIL-KN9204 was significantly higher than that of NIL-J411 across all the tested environments. Meanwhile, significant increases in plant height, grain width and 1000-grain weight were observed in NIL-KN9204 compared with that in NIL-J411. These results indicate that QFlw-5B has great potential for marker-assisted selection in wheat breeding programs designed to improve both plant architecture and yield. This study also provides a basis for the map-based cloning of QFlw-5B.

Genomic insights into the recent chromosome reduction of autopolyploid sugarcane Saccharum spontaneum

Saccharum spontaneum is a founding Saccharum species and exhibits wide variation in ploidy levels. We have assembled a high-quality autopolyploid genome of S. spontaneum Np-X (2n = 4x = 40) into 40 pseudochromosomes across 10 homologous groups, that better elucidates recent chromosome reduction and polyploidization that occurred circa 1.5 million years ago (Mya). One paleo-duplicated chromosomal pair in Saccharum, NpChr5 and NpChr8, underwent fission followed by fusion accompanied by centromeric split around 0.80 Mya. We inferred that Np-X, with x = 10, most likely represents the ancestral karyotype, from which x = 9 and x = 8 evolved. Resequencing of 102 S. spontaneum accessions revealed that S. spontaneum originated in northern India from an x = 10 ancestor, which then radiated into four major groups across the Indian subcontinent, China, and Southeast Asia. Our study suggests new directions for accelerating sugarcane improvement and expands our knowledge of the evolution of autopolyploids.

Wetting mechanism and morphological adaptation; leaf rolling enhancing atmospheric water acquisition in wheat crop-a review

Several plant species such as grasses are dominant in many habitats including arid and semi-arid areas. These species survive in these regions by developing exclusive structures, which helps in the collection of atmospheric water. Before the collected water evaporates, these structures have unique canopy structure for water transportation that plays an equivalent share in the fog-harvesting mechanism. In this review, the atmospheric gaseous water harvesting mechanisms and their affinity of measurements were discussed. Morphological adaptations and their role in the capturing of atmospheric gaseous water of various species were also discussed. The key factor for the water collection and its conduction in the wheat plant is the information of contact angle hysteresis. In wheat, leaf rolling and its association with wetting property help the plant in water retention. Morphological adaptations, i.e., leaf erectness, grooves, and prickle hairs, also help in the collection and acquisition of water droplets by stem flows in directional guide toward the base of the plant and allow its rapid uptake. Morphological adaptation strengthens the harvesting mechanism by preventing the loss of water through shattering. Thus, wheat canopy architecture can be modified to harvest the atmospheric water and directional movement of water towards the root zone for self-irrigation. Moreover, these morphological adaptations are also linked with drought avoidance and corresponding physiological processes to resist water stress. The combination of these traits together with water use efficiency in wheat contributes to a highly efficient atmospheric water harvesting system that enables the wheat plants to reduce the cost of production. It also increases the yielding potential of the crop in arid and semi-arid environments. Further investigating the ecophysiology and molecular pathways of these morphological adaptations in wheat may have significant applications in varying climatic scenarios.

Leaf Mutant 7 Encoding Heat Shock Protein OsHSP40 Regulates Leaf Size in Rice

Leaf size is an important agronomic trait directly affecting yield in rice, and thus understanding the genes determining leaf size is important in breeding. In this study, one Leaf Mutant 7 (lm7) with small leaf size was isolated using ethyl methane sulphonate (EMS) mutagenesis from the japonica Zhenggeng 1925. MutMap by whole genome resequencing of phenotypic bulks revealed that LM7 is likely located in the 133 kb region on chromosome 7 using F₂ population from a cross between lm7 and wild-type (WT) Zhenggeng 1925. The candidate gene encoding heat shock protein OsHSP40 for LM7 was functionally validated. Disruption of this gene in Oshsp40 mutants significantly reduced the leaf size compared with that of WT in rice. Microscopic examination showed that OsHSP40 modulated leaf size via regulating the veins formation and cell size/cell number. Nucleotide diversity analysis indicated that a single nucleotide polymorphism (SNP) variation of C to T in the coding region of OsHSP40 may cause small leaves among rice accessions. Therefore, the natural variation of OsHSP40 contributing to leaf size might be useful for rice breeding.

Closer vein spacing by ectopic expression of nucleotide-binding and leucine-rich repeat proteins in rice leaves

Elevated expression of nucleotide-binding and leucine-rich repeat proteins led to closer vein spacing and higher vein density in rice leaves. To feed the growing global population and mitigate the negative effects of climate change, there is a need to improve the photosynthetic capacity and efficiency of major crops such as rice to enhance grain yield potential. Alterations in internal leaf morphology and cellular architecture are needed to underpin some of these improvements. One of the targets is to generate a "Kranz-like" anatomy in leaves that includes decreased interveinal spacing close to that in C₄ plant species. As C₄ photosynthesis has evolved from C₃ photosynthesis independently in multiple lineages, the genes required to facilitate C₄ may already be present in the rice genome. The Taiwan Rice Insertional Mutants (TRIM) population offers the advantage of gain-of-function phenotype trapping, which accelerates the identification of rice gene function. In the present study, we screened the TRIM population to determine the extent to which genetic plasticity can alter vein density (VD) in rice. Close vein spacing mutant 1 (CVS1), identified from a VD screening of approximately 17,000 TRIM lines, conferred heritable high leaf VD. Increased vein number in CVS1 was confirmed to be associated with activated expression of two nucleotide-binding and leucine-rich repeat (NB-LRR) proteins. Overexpression of the two NB-LRR genes individually in rice recapitulates the high VD phenotype, due mainly to reduced interveinal mesophyll cell (M cell) number, length, bulliform cell size and thus interveinal distance. Our studies demonstrate that the trait of high VD in rice can be achieved by elevated expression of NB-LRR proteins limited to no yield penalty.

Morphological Characterization and Transcriptome Analysis of New Dwarf and Narrow-Leaf (dnl2) Mutant in Maize

Lodging is the primary factor limiting high yield under a high plant density. However, an optimal plant height and leaf shape can effectively decrease the lodging risk. Here we studied an ethyl methanesulfonate (EMS)-induced dwarf and a narrow-leaf mutant, dnl2. Gene mapping indicated that the mutant was controlled by a gene located on chromosome nine. Phenotypic and cytological observations revealed that dnl2 showed inhibited cell growth, altered vascular bundle patterning, and disrupted secondary cell wall structure when compared with the wild-type, which could be the direct cause of the dwarf and narrow-leaf phenotype. The phytohormone levels, especially auxin and gibberellin, were significantly decreased in dnl2 compared to the wild-type plants. Transcriptome profiling of the internodes of the dnl2 mutant and wild-type revealed a large number of differentially expressed genes enriched in the cell wall biosynthesis, remodeling, and hormone biosynthesis and signaling pathways. Therefore, we suggest that crosstalk between hormones (the altered vascular bundle and secondary cell wall structure) may contribute to the dwarf and narrow-leaf phenotype by influencing cell growth. These results provide a foundation for DNL2 gene cloning and further elucidation of the molecular mechanism of the regulation of plant height and leaf shape in maize.

CRISPR-Cas9-mediated mutagenesis of the SlSRM1-like gene leads to abnormal leaf development in tomatoes

BACKGROUND

Leaves, which are the most important organs of plants, can not only fix carbon sources through photosynthesis, but also absorb nutrients through transpiration. Leaf development directly determines the growth, flowering and fruiting of plants. There are many factors that affect leaf development, such as the growth environment, gene expression, and hormone synthesis. In this study, tomatoes were used to study the role of the transcription factor Solanum lycopersicum salt-related MYB1-like (SlSRM1-like) in the development of tomato leaves.

RESULTS

Loss-of-function of the SlSRM1-like gene mediated by clustered, regularly interspaced, short palindromic repeat (CRISPR)/CRISPR-associated 9 (Cas9) resulted in abnormal tomato leaf morphology, including thinner leaves, wrinkled edges, raised veins, disordered edge veins, and left and right asymmetry. An analysis of the transcription levels of genes related to leaf development revealed that the expression of these genes was significantly altered in the SlSRM1-like mutants (SlSRM1-like-Ms). Moreover, the SlSRM1-like gene was expressed at higher transcription levels in young tissues than in old tissues, and its expression was also induced in response to auxin. In addition, the transcription levels of genes related to the auxin pathway, which regulates tomato growth and development, were severely affected in the SlSRM1-like-Ms. Therefore, it is hypothesized that the SlSRM1-like gene functions in the regulation of tomato leaf development through the auxin-related pathway.

CONCLUSIONS

In this study, we successfully knocked out the SlSRM1-like gene in the tomato variety Ailsa Craig using CRISPR technology and found that knockout of the SlSRM1-like gene resulted in abnormal development of tomato leaves. Further research indicated that SlSRM1-like regulated tomato leaf development through auxin-related pathways. The results provide an important reference for the functional study of other SRM1-like genes in plants and provide new insights into the regulation of leaf development in tomato and other plants.

Pinpointing genomic regions associated with root system architecture in rice through an integrative meta-analysis approach

Applying an integrated meta-analysis approach led to identification of meta-QTLs/ candidate genes associated with rice root system architecture, which can be used in MQTL-assisted breeding/ genetic engineering of root traits. Root system architecture (RSA) is an important factor for facilitating water and nutrient uptake from deep soils and adaptation to drought stress conditions. In the present research, an integrated meta-analysis approach was employed to find candidate genes and genomic regions involved in rice RSA traits. A whole-genome meta-analysis was performed for 425 initial QTLs reported in 34 independent experiments controlling RSA traits under control and drought stress conditions in the previous twenty years. Sixty-four consensus meta-QTLs (MQTLs) were detected, unevenly distributed on twelve rice chromosomes. The confidence interval (CI) of the identified MQTLs was obtained as 0.11-14.23 cM with an average of 3.79 cM, which was 3.88 times narrower than the mean CI of the original QTLs. Interestingly, 52 MQTLs were co-located with SNP peak positions reported in rice genome-wide association studies (GWAS) for root morphological traits. The genes located in these RSA-related MQTLs were detected and explored to find the drought-responsive genes in the rice root based on the RNA-seq and microarray data. Multiple RSA and drought tolerance-associated genes were found in the MQTLs including the genes involved in auxin biosynthesis or signaling (e.g. YUCCA, WOX, AUX/IAA, ARF), root angle (DRO1-related genes), lateral root development (e.g. DSR, WRKY), root diameter (e.g. OsNAC5), plant cell wall (e.g. EXPA), and lignification (e.g. C4H, PAL, PRX and CAD). The genes located within both the SNP peak positions and the QTL-overview peaks for RSA are suggested as novel candidate genes for further functional analysis. The promising candidate genes and MQTLs can be used as basis for genetic engineering and MQTL-assisted breeding of root phenotypes to improve yield potential, stability and performance in a water-stressed environment.

Heterodimer formed by ROC8 and ROC5 modulates leaf rolling in rice

Moderately rolled leaf is one of the target traits of the ideal plant architecture in rice breeding. Many genes, including homeodomain leucine zipper IV transcription factors ROC5 and ROC8, regulating rice leaf rolling have been cloned and functionally analysed. However, the molecular mechanism by which these genes modulate leaf-rolling remains largely elusive. In this study, we demonstrated the transcription activation activity of both ROC8 and ROC5. Overexpressing ROC8 caused adaxially rolled leaves due to decreased number and size of bulliform cells, whereas knockout of ROC8 induced abaxially rolled leaves due to increased number and size of bulliform cells. ROC8 and ROC5 each could form homodimer, but ROC8 interacted preferably with ROC5 to forms a heterodimer. Importantly, we showed that the ROC8-ROC5 heterodimer rather than the homodimer of ROC8 or ROC5 was functional as neither overexpressing ROC8 in the ROC5 mutant nor overexpressing ROC5 in the ROC8-knockout line could rescue the mutant phenotype. This was further partially supported by the identification of a large number of common differentially expressed genes in single and double mutants of roc8 and roc5. ROC8 and ROC5 were functionally additive as the phenotype of abaxially rolled leaves was stronger in the roc5roc8 double mutant than in their single mutants. Our results provide evidence for the role of dimerization of ROC members in regulating leaf rolling of rice.

The legume-specific transcription factor E1 controls leaf morphology in soybean

BACKGROUND

The leaf is a determinate organ essential for photosynthesis, whose size and shape determine plant architecture and strongly affect agronomic traits. In soybean, the molecular mechanism of leaf development is not well understood. The flowering repressor gene E1, which encodes a legume-specific B3-like protein, is known to be the gene with the largest influence on soybean flowering and maturity. However, knowledge of its potential other functions remains poor.

RESULTS

Here, we identified a novel function of E1 protein in leaf development. Unifoliolate leaves of E1-overexpression (E1-OE) lines were smaller and curlier than those of wild type DongNong 50 (DN50) and Williams 82 (W82). Transverse histological sections showed disorganized cells and significantly elevated palisade tissue number, spongy tissue number, and bulliform cell number in E1-OE lines. Our results indicate that E1 binds to the promoters of the leaf- development-related CINCINNATA (CIN)-like TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) transcription factor genes to negatively regulate their expression.

CONCLUSIONS

Our findings identify E1 as an important new factor in soybean leaf development.

QTL mapping and candidate gene mining of flag leaf size traits in Japonica rice based on linkage mapping and genome-wide association study

BACKGROUND

As one of the most important factors of the japonica rice plant, leaf shape affects the photosynthesis and carbohydrate accumulation directly. Mining and using new leaf shape related genes/QTLs can further enrich the theory of molecular breeding and accelerate the breeding process of japonica rice.

METHODS

In the present study, 2 RILs and a natural population with 295 japonica rice varieties were used to map QTLs for flag leaf length (FL), flag leaf width (FW) and flag leaf area (FLA) by linkage analysis and genome-wide association study (GWAS) throughout 2 years.

RESULTS

A total of 64 QTLs were detected by 2 ways, and pleiotropic QTLs qFL2 (Chr2_33,332,579) and qFL10 (Chr10_10,107,835; Chr10_10,230,100) consisted of overlapping QTLs mapped by linkage analysis and GWAS throughout the 2 years were identified.

CONCLUSIONS

The candidate genes LOC_Os02g54254, LOC_Os02g54550, LOC_Os10g20160, LOC_Os10g20240, LOC_Os10g20260 were obtained, filtered by linkage disequilibrium (LD), and haplotype analysis. LOC_Os10g20160 (SD-RLK-45) showed outstanding characteristics in quantitative real-time PCR (qRT-PCR) analysis in leaf development period, belongs to S-domain receptor-like protein kinases gene and probably to be a main gene regulating flag leaf width of japonica rice. The results of this study provide valuable resources for mining the main genes/QTLs of japonica rice leaf development and molecular breeding of japonica rice ideal leaf shape.

Effect of an auxin biosynthesis inhibitor, p-phenoxyphenyl boronic acid, on auxin biosynthesis and development in rice

p-Phenoxyphenyl boronic acid (PPBo) is a specific inhibitor of auxin biosynthesis in Arabidopsis. We examined the inhibitory activity of PPBo in rice. The activity of OsYUCCA, a key enzyme for auxin biosynthesis, was inhibited by PPBo in vitro. The endogenous indole-3-acetic acid (IAA) level and the expression levels of auxin-response genes were significantly reduced in PPBo-treated rice seedlings, which showed typical auxin-deficiency phenotypes. Seminal root growth was promoted by 1 µM PPBo, which was reversed by co-treatment of IAA and PPBo. By contrast, the inhibition of root growth by 10 µM PPBo was not recovered by IAA. The root meristem morphology and cell division were restored by IAA at 60 µM, but that concentration may be too high to support root growth. In conclusion, PPBo is an inhibitor of auxin biosynthesis that targets YUCCA in rice.

Quantitative trait loci (QTL) analysis of leaf related traits in spinach (Spinacia oleracea L.)

BACKGROUND

Spinach (Spinacia oleracea L.) is an important leafy vegetable crop, and leaf-related traits including leaf length, leaf width, and petiole length, are important commercial traits. However, the underlying genes remain unclear. The objective of the study was to conduct QTL mapping of leaf-related traits in spinach.

RESULTS

A BC₁ population was used to construct the linkage map and for QTL mapping of leaf length, leaf width, petiole length, and the ratio of leaf length to width in 2015 and 2019. Two genetic linkage maps were constructed by specific locus amplified fragment sequencing (SLAF-seq), and kompetitive allele specific PCR (KASP) technology, respectively using BC₁ population in 2015. Based on the results of 2015, the specific linkage groups (LG) detected QTLs were generated using BC₁ population in 2019. A total of 13 QTLs were detected for leaf-related traits, only five QTLs being repeatedly detected in multiple years or linkage maps. Interestingly, the major QTLs of leaf length, petiole length, and the ratio of leaf length to width were highly associated with the same SNP markers (KM3102838, KM1360385 and KM2191098). A major QTL of leaf width was mapped on chromosome 1 from 41.470-42.045 Mb. And 44 genes were identified within the region. Based on the GO analysis, these genes were significantly enriched on ribonuclease, lyase activity, phosphodiester bond hydrolysis process, and cell wall component, thus it might change cell size to determine leaves shape.

CONCLUSIONS

Five QTLs for leaf-related traits were repeatedly detected at least two years or linkage maps. The major QTLs of leaf length, petiole length, and the ratio of leaf length to width were mapped on the same loci. And three genes (Spo10792, Spo21018, and Spo21019) were identified as important candidate genes for leaf width.

Narrow Leaf21, encoding ribosomal protein RPS3A, controls leaf development in rice

Leaf morphology influences photosynthesis, transpiration, and ultimately crop yield. However, the molecular mechanism of leaf development is still not fully understood. Here, we identified and characterized the narrow leaf21 (nal21) mutant in rice (Oryza sativa), showing a significant reduction in leaf width, leaf length and plant height, and increased tiller number. Microscopic observation revealed defects in the vascular system and reduced epidermal cell size and number in the nal21 leaf blade. Map-based cloning revealed that NAL21 encodes a ribosomal small subunit protein RPS3A. Ribosome-targeting antibiotics resistance assay and ribosome profiling showed a significant reduction in the free 40S ribosome subunit in the nal21 mutant. The nal21 mutant showed aberrant auxin responses in which multiple auxin response factors (ARFs) harboring upstream open-reading frames (uORFs) in their 5'-untranslated region were repressed at the translational level. The WUSCHEL-related homeobox 3A (OsWOX3A) gene, a key transcription factor involved in leaf blade lateral outgrowth, is also under the translational regulation by RPS3A. Transformation with modified OsARF11, OsARF16, and OsWOX3A genomic DNA (gDNA) lacking uORFs rescued the narrow leaf phenotype of nal21 to a better extent than transformation with their native gDNA, implying that RPS3A could regulate translation of ARFs and WOX3A through uORFs. Our results demonstrate that proper translational regulation of key factors involved in leaf development is essential to maintain normal leaf morphology.

OsARF11 Promotes Growth, Meristem, Seed, and Vein Formation during Rice Plant Development

The plant hormone auxin acts as a mediator providing positional instructions in a range of developmental processes. Studies in Arabidopsis thaliana L. show that auxin acts in large part via activation of Auxin Response Factors (ARFs) that in turn regulate the expression of downstream genes. The rice (Oryza sativa L.) gene OsARF11 is of interest because of its expression in developing rice organs and its high sequence similarity with MONOPTEROS/ARF5, a gene with prominent roles in A. thaliana development. We have assessed the phenotype of homozygous insertion mutants in the OsARF11 gene and found that in relation to wildtype, osarf11 seedlings produced fewer and shorter roots as well as shorter and less wide leaves. Leaves developed fewer veins and larger areoles. Mature osarf11 plants had a reduced root system, fewer branches per panicle, fewer grains per panicle and fewer filled seeds. Mutants had a reduced sensitivity to auxin-mediated callus formation and inhibition of root elongation, and phenylboronic acid (PBA)-mediated inhibition of vein formation. Taken together, our results implicate OsARF11 in auxin-mediated growth of multiple organs and leaf veins. OsARF11 also appears to play a central role in the formation of lateral root, panicle branch, and grain meristems.

OsYUC11-mediated auxin biosynthesis is essential for endosperm development of rice

Auxin is a phytohormone essential for plant development. However, our understanding of auxin-regulated endosperm development remains limited. Here, we described rice YUCCA (YUC) flavin-containing monooxygenase encoding gene OsYUC11 as a key contributor to auxin biosynthesis in rice (Oryza sativa) endosperm. Grain filling or storage product accumulation was halted by mutation of OsYUC11, but the deficiencies could be recovered by the exogenous application of auxin. A rice transcription factor (TF) yeast library was screened, and 41 TFs that potentially bind to the OsYUC11 promoter were identified, of which OsNF-YB1, a member of the nuclear factor Y family, is predominantly expressed in the endosperm. Both osyuc11 and osnf-yb1 mutants exhibited reduced seed size and increased chalkiness, accompanied by a reduction in indole-3-acetic acid biosynthesis. OsNF-YB1 can bind the OsYUC11 promoter to induce gene expression in vivo. We also found that OsYUC11 was a dynamically imprinted gene that predominantly expressed the paternal allele in the endosperm up to 10 d after fertilization (DAF) but then became a non-imprinted gene at 15 DAF. A functional maternal allele of OsYUC11 was able to recover the paternal defects of this gene. Overall, the findings indicate that OsYUC11-mediated auxin biosynthesis is essential for endosperm development in rice.

Genome-wide association study-based identification genes influencing agronomic traits in rice (Oryza sativa L.)

Rice is one of the most important cereal crops, providing the daily dietary intake for approximately 50% of the global human population. Here, we re-sequenced 259 rice accessions, generating 1371.65 Gb of raw data. Furthermore, we performed genome-wide association studies (GWAS) on 13 agronomic traits using 2.8 million single nucleotide polymorphisms (SNPs) characterized in 259 rice accessions. Phenotypic data and best linear unbiased prediction (BLUP) values of each of the 13 traits over two years of each trait were used for the GWAS. The results showed that 816 SNP signals were significantly associated with the 13 agronomic traits. Then we detected candidate genes related to target traits within 200 kb upstream and downstream of the associated SNP loci, based on linkage disequilibrium (LD) blocks in the whole rice genome. These candidate genes were further identified through haplotype block constructions. This comprehensive study provides a timely and important genomic resource for breeding high yielding rice cultivars.

QTL-Seq and Transcriptome Analysis Disclose Major QTL and Candidate Genes Controlling Leaf Size in Sesame (Sesamum indicum L.)

Leaf size is a crucial component of sesame (Sesamum indicum L.) plant architecture and further influences yield potential. Despite that it is well known that leaf size traits are quantitative traits controlled by large numbers of genes, quantitative trait loci (QTL) and candidate genes for sesame leaf size remain poorly understood. In the present study, we combined the QTL-seq approach and SSR marker mapping to identify the candidate genomic regions harboring QTL controlling leaf size traits in an RIL population derived from a cross between sesame varieties Zhongzhi No. 13 (with big leaves) and ZZM2289 (with small leaves). The QTL mapping revealed 56 QTL with phenotypic variation explained (PVE) from 1.87 to 27.50% for the length and width of leaves at the 1/3 and 1/2 positions of plant height. qLS15-1, a major and environmentally stable pleiotropic locus for both leaf length and width explaining 5.81 to 27.50% phenotypic variation, was located on LG15 within a 408-Kb physical genomic region flanked by the markers ZMM6185 and ZMM6206. In this region, a combination of transcriptome analysis with gene annotations revealed three candidate genes SIN_1004875, SIN_1004882, and SIN_1004883 associated with leaf growth and development in sesame. These findings provided insight into the genetic characteristics and variability for sesame leaf and set up the foundation for future genomic studies on sesame leaves and will serve as gene resources for improvement of sesame plant architecture.

Major QTLs, qARO1 and qARO9, Additively Regulate Adaxial Leaf Rolling in Rice

Moderate leaf rolling is considered optimal for the ideal plant type in rice (Oryza sativa L.), as it improves photosynthetic efficiency and, consequently, grain yield. Determining the genetic basis of leaf rolling via the identification of quantitative trait loci (QTLs) could facilitate the development of high-yielding varieties. In this study, we identified three stable rice QTLs, qARO1, qARO5, and qARO9, which control adaxial leaf rolling in a recombinant inbred line (RIL) population derived from a cross between Tong 88-7 (T887) and Milyang 23 (M23), using high-density SNP markers. These QTLs controlled the rolling phenotype of both the flag leaf (FL) and secondary leaf (SL), and different allelic combinations of these QTLs led to a wide variation in the degree of leaf rolling. Additive gene actions of qARO1 and qARO9 on leaf rolling were observed in a backcross population. In addition, qARO1 (markers: 01id4854718 and 01asp4916781) and qARO9 (markers: 09id19650402 and 09id19740436) were successfully fine-mapped to approximately 60- and 90-kb intervals on chromosomes 1 and 9, respectively. Histological analysis of near-isogenic lines (NILs) revealed that qARO1 influences leaf thickness across the small vein, and qARO9 affects leaf thickness in the entire leaf and bulliform cell area, thus leading to adaxial leaf rolling. The results of this study advance our understanding of the genetic and molecular bases of adaxial leaf rolling, and this information can be used for the development of rice varieties with the ideal plant type.

Curled Flag Leaf 2, Encoding a Cytochrome P450 Protein, Regulated by the Transcription Factor Roc5, Influences Flag Leaf Development in Rice

Moderate curling generally causes upright leaf blades, which favors the establishment of ideal plant architecture and increases the photosynthetic efficiency of the population, both of which are desirable traits for super hybrid rice (Oryza sativa L.). In this study, we identified a novel curled-leaf mutant, curled flag leaf 2 (cfl2), which shows specific curling at the base of the flag leaf owing to abnormal epidermal development, caused by enlarged bulliform cells and increased number of papillae with the disordered distribution. Map-based cloning reveals that CFL2 encodes a cytochrome P450 protein and corresponds to the previously reported OsCYP96B4. CFL2 was expressed in all analyzed tissues with differential abundance and was downregulated in the clf1 mutant [a mutant harbors a mutation in the homeodomain leucine zipper IV (HD-ZIP IV) transcription factor Roc5]. Yeast one-hybrid and transient expression assays confirm that Roc5 could directly bind to the cis-element L1 box in the promoter of CFL2 before activating CFL2 expression. RNA sequencing reveals that genes associated with cellulose biosynthesis and cell wall-related processes were significantly upregulated in the cfl2 mutant. The components of cell wall, such as lignin, cellulose, and some kinds of monosaccharide, were altered dramatically in the cfl2 mutant when compared with wild-type "Jinhui10" (WT). Taken together, CFL2, as a target gene of Roc5, plays an important role in the regulation of flag leaf shape by influencing epidermis and cell wall development.

Genome-wide identification and expression analysis of the TaYUCCA gene family in wheat

Auxin is an important endogenous hormone in plants. The YUCCA gene encodes a flavin monooxygenase, which is an important rate-limiting enzyme in the auxin synthesis pathway and involved in the regulation of plant growth and development. In the study, we identified 63 wheat TaYUCCA genes; among them, some genes appeared in clusters. By constructing phylogenetic trees, we found that the TaYUCCA genes could be divided into six groups. In the WheatExp database, there were 22 differential expressed TaYUCCA genes, among which the TaYUCCA10 gene was abundantly expressed in the endosperm and medium milk stage, the TaYUCCA2 gene was abundantly expressed in the roots of three leaves and meiosis and transfer cells at 20 days post anthesis and the others 16 TaYUCCA genes had different expression level at different developmental stages in wheat, and there were 15 TaYUCCA genes induced by drought and heat stress, among which the TaYUCCA2-D, TaYUCCA3-B, and TaYUCCA9-D might be upregulated induced by drought stress, TaYUCCA10.1 might be upregulated induced drought and heat stress, TaYUCCA6-A was upregulated induced both drought and heat stress and the others 9 TaYUCCA genes were downregulated induced by drought and heat stress. Transcriptome and qRT-PCR analysis showed that TaYUCCA7-A was upregulated significantly after induced by powdery mildew. The comprehensive annotation and expression profiling of the TaYUCCA genes in this study enhanced our understanding of TaYUCCA family gene expression in wheat growth and development and laid the foundation for the further study of TaYUCCA gene mechanism.

Investigation of the Genetic Diversity of a Rice Core Collection of Japanese Landraces using Whole-Genome Sequencing

The Rice Core Collection of Japanese Landraces (JRC) consisting of 50 accessions was developed by the genebank at the National Agriculture and Food Research Organization (NARO) in 2008. As a Japanese landrace core collection, the JRC has been used for many research projects, including screening for different phenotypes and allele mining for target genes. To understand the genetic diversity of Japanese Landraces, we performed whole-genome resequencing of these 50 accessions and obtained a total of 2,145,095 single nucleotide polymorphism (SNPs) and 317,832 insertion-deletions (indels) by mapping against the Oryza sativa ssp. japonica Nipponbare genome. A JRC phylogenetic tree based on 1,394 representative SNPs showed that JRC accessions were divided into two major groups and one small group. We used the multiple genome browser, TASUKE+, to examine the haplotypes of flowering genes and detected new mutations in these genes. Finally, we performed genome-wide association studies (GWAS) for agronomical traits using the JRC and another core collection, the World Rice Core Collection (WRC), comprising 69 accessions also provided by the NARO genebank. In leaf blade width, a strong peak close to NAL1, a key gene for the regulation of leaf width, and, in heading date, a peak near HESO1 involved in flowering regulation were observed in GWAS using the JRC. They were also detected in GWAS using the combined JRC + WRC. Thus, JRC and JRC + WRC are suitable populations for GWAS of particular traits.

Characterization of dwarf and narrow leaf (dnl-4) mutant in rice

Height and leaf morphology are important agronomic traits of the major crop plant rice (Oryza sativa). In previous studies, the dwarf and narrow leaf genes (dnl1, dnl2 and dnl3) have identified in rice. Using the Ac/Ds knockout system, we found a new dwarf and narrow leaf (dnl) mutant and identified mutated gene. The dnl-4 mutant showed reduced plant height and leaf blade width compared to the wild type, and increased leaf inclination. The morphological defects of the mutant were caused by the suppressed expression of the DNL-4 gene, which encodes a pfkB carbohydrate kinase protein. These results suggest that DNL-4 expression is involved in modulating plant height and leaf growth. Furthermore, DNL-4 expression also affects productivity in rice: the dnl-4 mutant exhibited reduced panicle length and grain width compared with the wild type. To understand DNL-4 function in rice, we analyzed the expression levels of leaf growth-related genes, such as NAL1, NAL7, and CSLD4, in the dnl-4 mutant. Expression of NAL1 and NAL7 was downregulated in the dnl-4 mutant compared to the wild type. The observation that DNL-4 expression corresponded with that of NAL1 and NAL7 is consistent with the narrow leaf phenotype of the dnl-4 mutant. These results suggest that DNL-4 regulates plant height and leaf structure in rice.

Fine Mapping of a Locus Underlying the Ectopic Blade-Like Outgrowths on Leaf and Screening Its Candidate Genes in Rapeseed (Brassica napus L.)

Leaf is an important organ for higher plants, and the shape of it is one of the crucial traits of crops. In this study, we investigated a unique aberrant leaf morphology trait in a mutational rapeseed material, which displayed ectopic blade-like outgrowths on the adaxial side of leaf. The abnormal line 132000B-3 was crossed with the normal line 827-3. Based on the F_{2 : 3} family, we constructed two DNA pools (normal pool and abnormal pool) by the bulked segregant analysis (BSA) method and performed whole genome re-sequencing (WGR), obtaining the single-nucleotide polymorphism (SNP) and insertion/deletion (InDel) data. The SNP-index method was used to calculate the Δ(SNP/InDel-index), and then an association region was identified on chromosome A10 with a length of 5.5 Mbp, harboring 1048 genes totally. Subsequently, the fine mapping was conducted by using the penta-primer amplification refractory mutation system (PARMS), and the associated region was narrowed down to a 35.1-kbp segment, containing only seven genes. These seven genes were then analyzed according to their annotations and finally, BnA10g0422620 and BnA10g0422610, orthologs of LATE MERISTEM IDENTITY1 (LMI1) gene from Arabidopsis and REDUCED COMPLEXITY (RCO) gene from its relative Cardamine hirsuta, respectively, were identified as the candidate genes responding to this blade-like outgrowth trait in rapeseed. This study provides a novel perspective into the leaf formation in Brassica plants.

QTL mapping and validation of bread wheat flag leaf morphology across multiple environments in different genetic backgrounds

Eight major and stably expressed QTL for flag leaf morphology across eleven environments were identified and validated using newly developed KASP markers in seven biparental populations with different genetic backgrounds. Flag leaf morphology is a determinant trait influencing plant architecture and yield potential in wheat (Triticum aestivum L.). A recombinant inbred line (RIL) population with a 55 K SNP-based constructed genetic map was used to map quantitative trait loci (QTL) for flag leaf length (FLL), width (FLW), area (FLA), angle (FLANG), opening angle (FLOA), and bend angle (FLBA) in eleven environments. Eight major QTL were detected in 11 environments with 5.73-54.38% of explained phenotypic variation. These QTL were successfully verified using the newly developed Kompetitive Allele Specific PCR (KASP) markers in six biparental populations with different genetic backgrounds. Among these 8 major QTL, two co-located intervals were identified. Significant interactions for both FLL- and FLW-related QTL were detected. Comparison analysis showed that QFll.sau-SY-2B and QFla.sau-SY-2B are likely new loci. Significant relationships between flag leaf- and yield-related traits were observed and discussed. Several genes associated with leaf development including the ortholog of maize ZmRAVL1, a B3-domain transcription factor involved in regulation of leaf angle, were predicted in physical intervals harboring these major QTL on reference genomes of bread wheat 'Chinese spring', T. turgidum, and Aegilops tauschii. Taken together, these results broaden our understanding on genetic basis of flag leaf morphology and provide clues for fine mapping and marker-assisted breeding wheat with optimized plant architecture for promising loci.