Rice Leaf Morphology Research Articles

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.

Genome-Wide Association Analysis of Rice Leaf Traits

Yield-related traits have always been a research hotspot in rice breeding, and functional leaves directly affect the photosynthetic efficiency and yield of rice. Therefore, it is of great significance to explore the genes related to rice leaf size and shape to improve rice leaf morphology, photosynthesis efficiency, and yield. This study detected the quantitative trait loci (QTLs) for the length, width, length–width ratio, and area of rice flag leaf and second leaf in 393 accessions from the 3000 Rice Genome Project (3KRGP) by high-density single-nucleotide polymorphism genotyping. As a result, 91 QTLs were detected, among which 5 candidate genes (LOC_Os03g29170, LOC_Os06g17285, LOC_Os04g35060, LOC_Os03g27450, and LOC_Os09g16280) were identified. In addition, the epistatic interactions affecting leaf-related traits were also investigated, resulting in the identification of 134 significant QQIs (QTL by QTL interactions) pairs. The results of this study provide an important genetic basis for mining genes associated with rice leaf shape and valuable genetic information for rice breeding.

RLM1, Encoding an R2R3 MYB Transcription Factor, Regulates the Development of Secondary Cell Wall in Rice.

Leaf morphology is an important component of rice ideal plant type. To date, many regulatory genes influencing leaf morphology in rice have been cloned, and their underlying molecular regulatory mechanism has been preliminarily clarified. However, the fine regulation relationship of leaf morphogenesis and plant type remains largely elusive. In this study, a rolling-leaf mutant, named rlm1-D, was obtained and controlled by a pair of dominant nuclear genes. Cytological observations revealed that the rlm1 was mainly caused by abnormal deposition of secondary cell walls. Molecular evidence showed ectopic expression of a MYB-type transcription factor LOC_Os05g46610 was responsible for the phenotype of rlm1-D. A series of experiments, including the transcription factor-centered technology, DNA-binding assay, and electrophoretic mobility shift assay, verified that RLM1 can bind to the promoter of OsCAD2, a key gene responsible for lignin biosynthesis in rice. An interacting partner of RLM1, OsMAPK10, was identified. Multiple biochemical assays confirmed that OsMAPK10 interacted with RLM1. OsMAPK10 positively regulated the lignin content in the leaves and stems of rice. Moreover, OsMAPK10 contributes to RLM1 activation of downstream target genes. In particular, RLM1 is exclusively expressed in the stems at the mature plant stage. The yield of RLM1 knockdown lines increased by over 11% without other adverse agricultural trait penalties, indicating great practical application value. A MAPK-MYB-OsCAD2 genetic regulatory network controlling SCW was proposed, providing a theoretical significance and practical value for shaping the ideal plant type and improving rice yield.

Nighttime transpirational cooling enabled by circadian regulation of stomatal conductance is related to stomatal anatomy and leaf morphology in rice.

Rice genotypes with larger stomata maintain higher nocturnal stomatal conductance, thus having lower nocturnal leaf temperature via transpirational cooling. Incomplete night stomatal closure has been widely observed, but the mechanisms and functions of nocturnal stomatal conductance (gs,n) are not fully understood. Stomatal anatomy, leaf morphology, gs,n and nocturnal leaf temperature (Tleaf,n) were measured in 30 Oryza genotypes. Nocturnal leaf conductance (gn) showed a significant circadian rhythm; it gradually increased by 58% from 20:30 to 04:30. Contrary to cuticular conductance (gcut), gs,n was highly correlated with gn. Moreover, gs,n accounted for 76% of gn. Tleaf,n was significantly lower than the air temperature, and was negatively correlated with both gs,n and nocturnal transpiration rate (En). gs,n was positively correlated with stomatal size, intervein distance between major veins (IVDmajor), leaf thickness (LT), individual leaf area (LA), and leaf width (LW). It was also found negatively correlated with stomatal density. Reversely, Tleaf,n was negatively correlated with stomatal size, IVDmajor, intervein distance between minor veins, LA and LW. Tleaf,n presented a positive correlation with stomatal density. This study highlights the importance of stomatal anatomy and leaf morphology on regulating gs,n and Tleaf,n. The underlying mechanisms to the determinants of gs,n and the physiological and ecological functions of the Tleaf,n regulation on rice growth and production were carefully discussed.

Quantitative Evaluation of Leaf Morphology with Different Rice Genotypes Based on Image Processing

Prostrate growth 1 (PROG1) gene is vital in controlling the prostrate growth habit of rice. Studying the effect of PROG1 gene on rice canopy structure is crucial in elucidating the molecular mechanism of rice plant type evolution. Herein, the morphological characteristics of different rice genotypes were collected at different growth stages and leaf nodes using image processing techniques. The morphological characteristics included leaf length, leaf width, and leaf area. The image processing techniques involved boundary mean oscillation (BMO) filtering and minimum bounding rectangle extraction of the target image. On this basis, the effect of the PROG1 gene on rice leaf morphology was quantitatively assessed. Also, the feasibility of image processing techniques in detecting the morphological characteristics of rice leaves was discussed. Under the influence of the PROG1 gene, the length, width, and area of rice leaves decreased by 45.1%, 12.7%, and 44.8%, respectively, at the booting stage. Similarly, the length, width, and area of flag leaves decreased by 15.8%, 32.0%, and 33.7% at the heading stage and by 25.4%, 16.2%, and 19.7% at the filling stage, respectively, and that of secondary leaf reduced by 23.2%, 13.6%, and 54.2% at heading stage and by 24.1%, 17.3%, and 37.0% at filling stage, respectively. Furthermore, the length, width, and area of other leaves reduced by 32.3%, 9.8%, and 51.6% at the heading stage and by 28.6%, 7.3%, and 36.7% at the filling stage, respectively. The leaves in the rice canopy were shorter, narrower, and smaller in leaf area. Notably, no significant differences were found between image processing technology and manual measurement methods regarding the values of leaf morphological characteristics obtained ( P < 0.05 ). Thus, these results show that image processing technology is effective in studying the morphological characteristics of rice leaves. This study provides a reliable foundation for molecular breeding studies and will guide the application of the PROG1 gene in molecular breeding.

QTL mapping and analysis of candidate genes in flag leaf morphology in rice

<p indent=0mm>Leaf is an important organ of rice, and it is the main place for photosynthesis. Leaf morphology related traits such as leaf length, leaf width and leaf area can directly affect leaf photosynthetic efficiency. The study of quantitative trait loci (QTL) sites for morphological characters of rice flag leaf and the improvement of morphological characters of rice flag leaf by means of genetic breeding can provide theoretical basis for the cultivation of ideal plant type rice. In this study, an indica rice variety HZ was used as the male parent, and a japonica rice variety Nekken2 was used as the female parent. After F1 generation was obtained by cross-breeding, 120 recombinant inbred lines (RIL populations) were obtained from successive generations of self-crossing, which were used as experimental materials in this study. Leaf length, leaf width, leaf area of rice at tillering stage and mature stage were studied and analyzed after incubation under the same and appropriate conditions. At the same time, the genetic map was constructed by using the RIL population to locate the QTLs for the traits of leaf length, leaf width and leaf area in rice at tillering stage and mature stage, 35 QTLs related to leaf morphology were detected. There were 6 QTLs related to blade length (5 at tillering stage, 1 at maturation stage), LOD value of one of them was as high as 6.92; 8 QTLs related to blade width (detected only at tillering stage), LOD value of one was as high as 4.51; 21 QTLs related to blade area (12 at tillering stage, 9 at mature stage), LOD values of two of them were as high as 6.37 and 4.06 respectively. Through quantitative analysis of the candidate genes related to leaf length, leaf width and leaf area in these QTL regions, it was found that<italic> LOC_Os02g52040</italic>, <italic>LOC_Os03g46610</italic>,<italic> LOC_Os04g52230</italic>,<italic> LOC_Os04g42230</italic>,<italic> LOC_Os04g44150</italic>,<italic> LOC_Os04g52479</italic>,<italic> LOC_Os09g37400 </italic>and <italic>LOC_Os12g42020</italic> were significantly different in expression levels between the parents. Combined with the data of leaf length, leaf width and leaf area of the parents, we speculated that The high expressions of<italic> LOC_Os04g52230</italic>, <italic>LOC_Os04g44150</italic>,<italic> LOC_Os09g37400 </italic>and <italic>LOC_Os12g42020</italic> may promote the growth of leaf width and leaf area, while the high expressions of <italic>LOC_Os02g52040</italic>, <italic>LOC_Os03g46610 </italic>and <italic>LOC_Os04g52479 </italic>may inhibit the growth of rice flag leaves. Through the analysis of QTL in this study, QTL regulating leaf length, leaf width and leaf area of rice flag leaf were excavated, which provided a reference for cultivating new rice varieties with excellent plant type.

HD-ZIP IV gene Roc8 regulates the size of bulliform cells and lignin content in rice.

The morphology of bulliform cells located on the upper epidermis of leaves is one of the most important cell structures affecting leaf shape. Although many mechanisms regulating the development of bulliform cells have been reported, the fine regulatory mechanisms governing this process have rarely been described. To identify novel components regulating rice leaf morphology, a mutant showing a constitutively rolling phenotype from the seedling stage to flowering, known as crm1‐D, was selected for further analysis. Anatomical analyses in crm1‐D were attributable to the size reduction of bulliform cells. The crm1‐D was controlled by a single dominant nuclear gene. Map‐based cloning revealed that Roc8, an HD zipper class IV family member, was responsible for the crm1‐D phenotype. Notably, the 50‐bp sequence in the 3′‐untranslated region (3′‐UTR) of the Roc8 gene represses Roc8 at the translational level. Moreover, the roc8 knockdown lines notably increased the size of bulliform cells. A series of assays revealed that Roc8 negatively regulates the size of bulliform cells. Unexpectedly, Roc8 was also observed to positively mediate lignin biosynthesis without incurring a production penalty. The above results show that Roc8 may have a practical application in cultivating materials with high photosynthetic efficiency and low lignin content.

CRISPR/Cas9-Induced Mutagenesis of Semi-Rolled Leaf1,2 Confers Curled Leaf Phenotype and Drought Tolerance by Influencing Protein Expression Patterns and ROS Scavenging in Rice (Oryza sativa L.)

Rice leaf morphology is an essential agronomic trait to develop drought-tolerant genotypes for adequate and stable crop production in drought-prone areas. Here, rolled leaf mutant plants were acquired by CRISPR/Cas9-based mutagenesis of Semi-rolled leaf1,2 (SRL1 and SRL2) genes, and isobaric tags for relative and absolute quantification (iTRAQ) based proteomic analysis was performed to analyze the subsequent proteomic regulation events. Homozygous mutants exhibit decreased chlorophyll content, transpiration rate, stomatal conductance, vascular bundles (VB), stomatal number, and agronomic traits with increased panicle number and bulliform cells (BCs). Under drought stress, mutant plants displayed lower malondialdehyde (MDA) content while higher survival rate, abscisic acid (ABA) content, superoxide dismutase (SOD), catalase (CAT) activities, and grain filling percentage compare with their wild type (WT). Proteomic results revealed that 270 proteins were significantly downregulated, and 107 proteins were upregulated in the mutant line compared with WT. Proteins related to lateral organ boundaries’ (LOB) domain (LBD) were downregulated, whereas abiotic stress-responsive proteins were upregulated in the CRISPR mutant. LBD proteins (Q5KQR7, Q6K713, Q7XGL4, Q8LQH4), probable indole-3-acetic acid-amido synthetase (Q60EJ6), putative auxin transporter-like protein 4 (Q53JG7), Monoculm 1 (Q84MM9) and AP2 (Apetala2) domain-containing protein (Q10A97) were found to be hub-proteins. The hybrids developed from mutant restorers showed a semi-rolled leaf phenotype with increased panicle number, grain number per panicle, and yield per plant. Our findings reveal the intrinsic value of genome editing and expand the knowledge about the network of proteins for leaf rolling and drought avoidance in rice.

DLT/OsGRAS-32, regulating leaf width and thickness by controlling cell number in Oryza sativa

The improvement of rice leaf morphology is an important goal of rice plant breeding. Studying its molecular development mechanism will facilitate the breeding of a maximally efficient plant type. To further study the developmental mechanism of rice leaves, a dwarf broad-leaf mutant, g44, was obtained by ethyl methanesulfonate mutagenesis of the rice restorer line Jinhui10, and genetic analysis indicated that the trait was controlled by a pair of recessive nuclear gene. The locus was fine mapped on chromosome 6 with 16-kb physical distance. Sequencing revealed that an A-T base substitution occurred in the mutant, resulting in the early termination of LOC_Os06g03710/DLT translation in g44 and yielding only one residual peptide containing 558 amino acids. The phenotypic and sequencing results of the complementary transgenic plants and the allelic mutant g44-1 further confirmed this result. Mutant plants grown under field conditions showed dwarfing, a leaf colour of dark green, leaf widening, and grain enlargement. Paraffin section and cryosection analysis showed that the increase in the number of large vascular bundles and small vascular bundles and the increase in the spacing between adjacent small vascular bundles were the main reasons for the broadening of mutant leaves. In addition, the increase in thickness of the mesophyll cell layer may be the main reason for the increase in leaf colour darkness and net photosynthetic rate. The qPCR results preliminarily predicted that the increase in the number of mutant cells was caused by an enhanced cell division ability, and the DLT/G44 gene was proposed to participate in the regulation of cell division by suppressing the expression of cyclin-related genes.

Rice Morphogenesis and Chlorophyll Accumulation Is Regulated by the Protein Encoded by NRL3 and Its Interaction With NAL9.

Rice yield is closely related to plant leaf shape and chlorophyll content. In this study, we isolated and identified a narrow and rolled leaf mutant, temporarily named nrl3 with darker green leaves. Histological analysis showed that nrl3 has a reduced number of vascular bundles and undergoes abnormal abaxial sclerenchymatous cell differentiation. The NRL3 mutant phenotype was controlled by a single recessive gene, fine-mapped to a 221 kb interval between Indel3 and RM2322 on Chr3. There are 42 ORF in this interval. Sequencing identified an SNP mutant leading to a premature stop in ORF 18, the candidate gene. Bioinformation analysis indicated that NRL3 encodes a novel protein with unknown function. NRL3 is localized in cytoplasm, membrane and nucleus. Expression analysis of nrl3 showed that genes involved in chlorophyll synthesis were significantly up-regulated while those involved in chlorophyll degradation and programmed cell death (PCD) were significantly down-regulated. The expression levels of photosynthesis genes were also affected. Y2H and BIFC assays indicated that NRL3 interacts directly with NAL9/VYL to regulate leaf morphology in rice. Thus, NRL3 plays an important role in leaf morphogenesis and chlorophyll accumulation, and can be used as a new gene resource for constructing improved rice.

Current Advances in Molecular Basis and Mechanisms Regulating Leaf Morphology in Rice.

Yield is majorly affected by photosynthetic efficiency. Leaves are essential structure for photosynthesis and their morphology especially size and shape in a plant canopy can affect the rate of transpiration, carbon fixation and photosynthesis. Leaf rolling and size are considered key agronomic traits in plant architecture that can subsidize yield parameters. In last era, a number of genes controlling leaf morphology have been molecularly characterized. Despite of several findings, our understanding toward molecular mechanism of leaf rolling and size are under-developed. Here, we proposed a model to apprehend the physiological basis of different genes organized in a complex fashion and govern the final phenotype of leaf morphology. According to this leaf rolling is mainly controlled by regulation of bulliform cells by SRL1, ROC5, OsRRK1, SLL2, CLD1, OsZHD1/2, and NRL1, structure and processes of sclerenchyma cells by SLL1 and SRL2, leaf polarity by ADL1, RFS and cuticle formation by CFL1, and CLD1. Many of above mentioned and several other genes interact in a complex manner in order to sustain cellular integrity and homeostasis for optimum leaf rolling. While, leaf size is synchronized by multifarious interaction of PLA1, PLA2, OsGASR1, and OsEXPA8 in cell division, NAL1, NAL9, NRL1, NRL2 in regulation of number of veins, OsCOW1, OsPIN1, OsARF19, OsOFP2, D1 and GID in regulation of phytohormones and HDT702 in epigenetic aspects. In this review, we curtailed recent advances engrossing regulation and functions of those genes that directly or indirectly can distress leaf rolling or size by encoding different types of proteins and genic expression. Moreover, this effort could be used further to develop comprehensive learning and directing our molecular breeding of rice.

Utilization of Machine Vision to Monitor the Dynamic Responses of Rice Leaf Morphology and Colour to Nitrogen, Phosphorus, and Potassium Deficiencies

Machine vision technology enables the continuous and nondestructive monitoring of leaf responses to different nutrient supplies and thereby contributes to the improvement of diagnostic effects. In this study, we analysed the temporal dynamics of rice leaf morphology and colour under different nitrogen (N), phosphorus (P), and potassium (K) treatments by continuous imaging and further evaluated the effectiveness of dynamic characteristics for identification. The top four leaves (the 1st incomplete leaf and the top three fully expanded leaves) were scanned every three days, and all images were processed in MATLAB to extract the morphological and colour characteristics for dynamic analysis. Subsequently, the mean impact value was applied to evaluate the effectiveness of dynamic indices for identification. According to the results, higher nutrient supply resulted in a faster leaf extension rate and a lower developing rate of chlorosis, and the influence of N deficiency on leaf growth was the greatest, followed by P deficiency and then K deficiency. Furthermore, the optimal indices for identification were mainly calculated from morphological characteristics of the 1st incomplete leaf and colour characteristics of the 3rd fully expanded leaf. Overall, dynamic analysis contributes not only to the exploration of the plant growth mechanism but also to the improvement of diagnostics.

Research on the Rice Leaf Morphological Formation and its Visualization

This paper firstly summarizes the morphological characteristics of rice leaf through observation of the rice leaf growth process. And then the mathematical model of the rice leaf growing is established based on experimental data. In this model, the vectorization of rice leaf morphology and growth process is realized by only several explicit biological parameters. The visualization of the rice leaf growth process is realized in computer by technique of computer graphics and the combination of VC++ and OpenGL. The simulation results show that the proposed model can simulate the growth process of the rice leaf very well on the computer easily with less parameter.

Leaf folding behaviour of Cnaphalocrocis medinalis (Guenee) and Marasmia patnalis Bradley, and the influence of rice leaf morphology on damage incidence

The leaf-folding behaviour of the pyralid rice leaf-folders (RLF), Cnaphalocrods medinalis (Guenee) and Marasmia patnalis Bradley, and the mechanism of fold construction were studied at the Bangladesh Rice Research Institute's experimental farm at Gazipur, Bangladesh during 1992 and 1993. Mature RLF larvae (instars III–V) usually folded rice leaves longitudinally with the abaxial surface inside the folds, while younger instars partially rolled the leaf edges. Folds were made along the middle portion of upper leaves. Larvae faced difficulties in making folds on narrower leaves which probably afforded less protection from harsh weather and natural enemies. These studies and observations broadened the understanding and knowledge regarding the actual procedure of leaf folding and led to the development of a hypothesis that rice plants having narrow leaf blades may offer resistance to RLF. A field test with 16 rice varieties and breeding lines with differences in leaf blade width and length correlated with the hypothesis. Tests also indicated that longer and tougher leaf blades might also contribute to resistance. It appeared that rice leaf blade morphology i.e. width, length, and toughness, may play a vital role in resistance against RLF. RLF resistance in TKM6 is suspected to be a combination of antixenosis and antibiosis.