Leaf Shape Development Research Articles

Herbarium specimens reveal links between leaf shape of Capsella bursa-pastoris and climate.

Studies into the evolution and development of leaf shape have connected variation in plant form, function, and fitness. For species with consistent leaf margin features, patterns in leaf architecture are related to both biotic and abiotic factors. However, for species with inconsistent leaf shapes, quantifying variation in leaf shape and the effects of environmental factors on leaf shape has proven challenging. To investigate leaf shape variation in a species with inconsistently shaped leaves, we used geometric morphometric modeling and deterministic techniques to analyze approximately 500 digitized specimens of Capsella bursa-pastoris collected throughout the continental United States over 100 years. We generated a morphospace of the leaf shapes and modeled leaf shape as a function of environment and time. Leaf shape variation of C. bursa-pastoris was strongly associated with temperature over its growing season, with lobing decreasing as temperature increased. While we expected to see changes in variation over time, our results show that the level of leaf shape variation was consistent over the 100 years. Our findings showed that species with inconsistent leaf shape variation can be quantified using geometric morphometric modeling techniques and that temperature is the main environmental factor influencing leaf shape variation.

A single nucleotide substitution in BnaC02.LBD6 promoter causes blade shape variation in Brassica napus

Leaf shape is a part of ideotype. Appropriate leaf rolling aids compact plant architecture. Oilseed is a crucial crop, but the genetic basis for leaf shape development in rapeseed (Brassica napus) is unclear, and no corresponding genetic improvement germplasm resources are available. We identified a dominant mutant, INSIDE-ROLLING LEAF1 (IRL1), in rapeseed with internal rolling of leaves due to abnormal mesophyll cell development. It had drooped siliques and a semi-dwarf stature, reducing of one to two effective branch numbers. Map-based cloning and complementary validation confirmed BnaC02G0201100ZS as causal gene IRL1. BnaC02G0201100ZS encodes LATERAL ORGAN BOUNDARIES DOMAIN6 (BnaC02.LBD6). Phenotypic variation of the irl1 mutant was due to an increase in BnaC02.LBD6 expression owing to a single nucleotide substitution at the DNA binding site in the promoter. Phenotype of plants overexpressing BnaC02.LBD6 was similar to that of the irl1 mutant. Haploid analysis showed a rare variation in BnaC02.LBD6 promoter, resulting in a unique phenotype in the irl1 mutant. Transcriptome analysis showed the differential expression of genes related to leaf adaxial–abaxial polarity development, secondary metabolic processes, and hormone signalling pathways. We provide novel insights into rapeseed: the genetic basis of variation in leaf characteristics and valuable genetic resources for plant architecture improvement.

Auxin-related MYB (CaSRM1) is involved in leaf shape development and reproductive growth in pepper (Capsicum annuum L.)

Pepper is among the most economically important solanaceous vegetable crops worldwide. The shape and spatial distribution of leaves affect the light energy use efficiency of the plant, which strongly affects the yield and quality of pepper fruit. However, the molecular mechanisms underlying pepper leaf development are unknown. In this study, we demonstrated that the CaSRM1 gene regulates pepper leaf morphology. Virus-induced gene silencing was used to reveal that silencing of CaSRM1 caused development of uneven leaf margins and curling of pepper leaves. Overexpression of CaSRM1 in tomato led to leaf morphological defects, but was accompanied by improved vegetative growth and larger fruit. The expression level of CaSRM1 in mature tissues was higher than that in young tissues of pepper plant, and its expression was induced by auxin. Analysis of phytohormone contents and expression of leaf shape-related genes revealed that the auxin content showed an opposite trend to CaSRM1 expression, and certain leaf shape-related genes were affected by CaSRM1 expression, especially auxin-related genes. The results provide important information for functional research on other SRM1 genes and offer a novel perspective to the mechanism of plant leaf and fruit development.

Functional and historical drivers of leaf shape evolution in palms (Arecaceae)

AbstractAimLeaves display a remarkable variety of shapes, each with potential ecological advantages in specific climates. While the relations between leaf shape and either climate or height have been relatively well studied in eudicots, the macroecological drivers of shape remain poorly known in monocots. Here, we investigated the associations between climate and plant height with the evolution of leaf shape in a clade with high species and morphological diversity.LocationGlobal.Time periodCretaceous to contemporary.Major taxa studiedPalms (Arecaceae).MethodsWe apply a Bayesian phylogenetic mixed model to test for associations between climate and leaf shape (all – entire‐leaved, pinnate‐dissected, palmate‐dissected and costapalmate). We further reconstruct the ancestral leaf shape using multistate speciation and extinction models and compare the frequency of shapes with global temperatures through time.ResultsWe find that plant height associates with dissected leaves and that annual precipitation associates with pinnate shapes. The ancestral leaf shape is unclear, but early diversification was dominated by pinnate‐dissected palms, which has remained the most species‐rich form of leaves throughout palm history.Main ConclusionsPalms that are tall and live in humid regions are more likely to have pinnate leaves. Through geological time scales, temperature did not play an obvious role in determining leaf shapes. This study contributes to our understanding of how the diversity of leaf shapes is linked to biological and climatic factors.

HD-Zip Transcription Factor is Responsible for No-Lobed Leaf in Watermelon (Citrullus lanatus L.)

Leaf is a vital organ of plants that plays an essential role in photosynthesis and respiration. As an important agronomic trait in leaf development, leaf shape is classified into lobed, entire (no-lobed), and serrated in most crops. In this study, two-lobed leaf watermelon inbred lines WT2 and WCZ, and a no-lobed leaf watermelon inbred line WT20 were used to create two F2 populations. Segregation analysis suggested that lobed leaves were dominant over the no-lobed leaves, and it was controlled by a signal gene. A locus on watermelon chromosome 4 controlling watermelon lobed/no-lobed leaves was identified through BSA-seq strategy combined with linkage analysis. The candidate gene was fine-mapped to a 61.5 kb region between 21,224,481 and 21,285,957 bp on watermelon chromosome 4 using two F2 populations. Four functional genes were annotated in the candidate region, while sequences blast showed that there was a single-base deletion (A/-) only in the exon of Cla018360, which resulted in premature termination of translation in the no-lobed leaf lines. Function prediction showed that Cla018360 encodes an HD-Zip protein that has been reported to regulate the development of leaf shape. The single-base deletion also occurred in the HD-Zip domain. We inferred that the Cla018360 gene is the candidate gene for regulating the development of lobed/no-lobed leaves in watermelon. Gene expression analysis showed that Cla018360 was highly expressed in young leaves. Phylogenetic analysis showed that Cla018360 had a close genetic relationship with AtHB51, which had been reported to regulate the formation of leaf shape in Arabidopsis. Furthermore, transcriptome analysis showed that a total of 333 differentially expressed genes were identified between WT2 and WT20, of which 115 and 218 genes were upregulated and downregulated in no-lobed leaved watermelon WT20. This study not only provides a good entry point for studying leaf development but also provides foundational insights into breeding for special plant architecture in watermelon.

Identification and analysis of HD‐Zip genes involved in the leaf development of Liriodendron chinense using multidimensional analysis

Homeodomain-leucine zipper (HD-Zip) proteins are plant-specific transcription factors that play important roles in different biological processes, especially leaf development. However, no studies to date have identified the HD-Zip genes in Liriodendron chinense nor characterized their functions. We identified the HD-Zip genes in L. chinense by analysing the phylogeny, chromosome location, structure, conserved motif, cis-regulatory elements, synteny, post-transcriptional regulation and expression patterns of these genes during leaf development. A total of 36 LcHD-Zip genes were identified and divided into four subfamilies (HD-Zip I to IV). Synteny analysis revealed that segmental duplication was the main force driving the expansion of LcHD-Zip genes. These 36 LcHD-Zip genes exhibited 11 different expression patterns. Pattern 1, 2, 3, 4, 6, 7, 8 and 9 genes may play important roles in leaf development, such as leaf initiation, leaf polarity establishment, leaf shape development, phytohormone-mediated leaf growth and leaf epidermal structure formation. Four HD-Zip III genes were targeted by microRNAs (miRNAs), and the miR165/166a-HD-Zip regulatory module formed regulated leaf initiation and leaf polarity establishment. Overall, LcHD-Zip genes play key roles in leaf development of L. chinense. This work provides a foundation for the functional verification of HD-Zip genes identified in this study.

CiKN1 and CiKN6 are involved in leaf development in citrus by regulating CimiR164.

SUMMARYLeaf shape is an important agronomic trait that is involved in plant photosynthesis, flowering, disease resistance, and yield. In recent years, many leaf shape‐related genes have been identified in model plants, but the precise regulatory network of leaf shape development remains unclear, particularly in woody plants. Transcriptome analysis of trifoliate orange and lemon leaves revealed that two citrus Knotted1‐like (CiKN1 and CiKN6) genes might participate in leaf development. Overexpression of CiKN1 displays lobed leaves in simple leaf Arabidopsis and lemon. Further protein interaction analysis revealed that CiKN6 interacted with CiKN1, whose overexpression resulted in deeper lobed leaves in transgenic Arabidopsis and lemon. Suppressing CiKN6 expression also affected the development of lemon leaves. Furthermore, we found that the CiKN1–CiKN6 complex specifically binds to the citrus miR164a promoter and suppresses its expression. In addition, a SQUAMOSA promoter binding protein‐like (SPL) gene (CiSPL11) was identified using yeast one‐hybrid assays and was found to promote CiKN6 transcription by binding to its promoter. Transgenic Arabidopsis showed that CiSPL11 might be involved in the development of citrus leaves. These results suggested that the CiKN1–CiKN6 complex and miR164a interact to regulate leaf development in citrus.

Identification and regulatory network analysis of SPL family transcription factors in Populus euphratica Oliv. heteromorphic leaves

The SQUAMOSA promoter-binding protein-like (SPL) family play a key role in guiding the switch of plant growth from juvenile to adult phases. Populus euphratica Oliv. exhibit typical heterophylly, and is therefore an ideal model for studying leaf shape development. To investigate the role and regulated networks of SPLs in the morphogenesis of P. euphratica heteromorphic leaves. In this study, 33 P. euphratica SPL (PeuSPL) genes were identified from P. euphratica genome and transcriptome data. Phylogenetic analysis depicted the classification of these SPL genes into two subgroups. The expression profiles and regulatory networks of P. euphratica SPL genes analysis displayed that major P. euphratica SPL family members gradually increases from linear to broad-ovate leaves, and they were involved in the morphogenesis regulation, stress response, transition from vegetative to reproductive growth, photoperiod, and photosynthesis etc. 14 circRNAs, and 33 lncRNAs can promote the expression of 12 of the P. euphratica SPLs by co-decoying miR156 in heteromorphic leaf morphogenesis. However, it was found that the effect of PeuSPL2-4 and PeuSPL9 in leaf shape development was contrasting to their homologous genes of Arabidopsis. Therefore, it was suggested that the SPL family were evolutionarily conserved for regulation growth, but were varies in different plant for regulation of the organ development.

Population Structure Analysis and Genome-Wide Association Study of Tea (Camellia sinensis (L.) Kuntze) Germplasm in Qiannan, China, Based on SLAF-Seq Technology

Duyun Maojian tea is a famous tea in China. In this study, the specific-locus amplified fragment (SLAF) sequencing method was used to analyze the population structure and conduct a genome-wide association study (GWAS) of 2 leaf traits of 123 tea plants in Qiannan, China. A total of 462,019 SLAF tags and 11,362,041 single-nucleotide polymorphism (SNP) loci were obtained. The results of phylogenetic tree analysis, cluster analysis, and principal component analysis showed that 123 tea germplasms were clustered into three groups, and the heterozygosity rates for Groups I, II, and II were 0.206, 0.224, and 0.34, respectively. Generally, tea germplasms in a production area are clustered in a group, indicating that tea germplasms in different production areas have certain genetic diversity. The traditional Duyun Maojian tea core production areas, TS and DC-SJ, are clustered into Group I and Group II respectively, while the ZY production area is relatively independent in Group III. Furthermore, based on GWAS analysis, 11 candidate genes related to leaf apex and 7 candidate genes related to leaf shape were obtained. This study clarified the genetic relationship among eight Duyun Maojian tea production areas and obtained candidate genes related to leaf apex and leaf shape development. The results showed that population structure and candidate genes are an effective basis for the breeding of Duyun Maojian tea germplasm.

Genome-Wide Association Study Reveals Genomic Region Associated with Mite-Recruitment Phenotypes in the Domesticated Grapevine (Vitis vinifera).

Indirect defenses are plant phenotypes that reduce damage by attracting natural enemies of plant pests and pathogens to leaves. Despite their economic and ecological importance, few studies have investigated the genetic underpinnings of indirect defense phenotypes. Here, we present a genome-wide association study of five phenotypes previously determined to increase populations of beneficial (fungivorous and predacious) mites on grape leaves (genus Vitis): leaf bristles, leaf hairs, and the size, density, and depth of leaf domatia. Using a common garden genetic panel of 399 V. vinifera cultivars, we tested for genetic associations of these phenotypes using previously obtained genotyping data from the Vitis9kSNP array. We found one single nucleotide polymorphism (SNP) significantly associated with domatia density. This SNP (Chr5:1160194) is near two genes of interest: Importin Alpha Isoform 1 (VIT_205s0077g01440), involved in downy mildew resistance, and GATA Transcription Factor 8 (VIT_205s0077g01450), involved in leaf shape development. Our findings are among the first to examine the genomic regions associated with ecologically important plant traits that facilitate interactions with beneficial mites, and suggest promising candidate genes for breeding and genetic editing to increase naturally occurring predator-based defenses in grapevines.

Genomic and niche divergence in an Amazonian palm species complex

AbstractEnvironmental heterogeneity across the landscape can cause lineage divergence and speciation. The Geonoma macrostachys (Arecaceae) species complex has been proposed as a candidate case of ecological speciation in Amazonia due to evidence of habitat partitioning and pre-zygotic reproductive barriers between co-occurring morphotypes at a local scale. In this study, we provide a continent-wide perspective of the divergence patterns in G. macrostachys by integrating data from morphological traits, target sequence capture, climate, soil and reproductive biology. A morphometric analysis revealed four morphogroups, defined by traits related to leaf shape. A coalescence-based phylogenetic analysis did not recover the morphogroups as monophyletic, indicating independent evolution of leaf shape across geographical space. We demonstrate scale-dependent habitat differentiation for two of the morphogroups, in which segregation driven mostly by climate was complete at the regional scale but incomplete at the continental scale. Contrary to previous evidence of reproductive isolation in the form of different pollinators and flowering times between sympatric G. macrostachys forms in Peru and Ecuador, these were not found in Colombia, suggesting reproductive barriers have evolved multiple times across its geographical range. Taken together, our findings suggest that ecological divergence and local adaptation is driving diversification in G. macrostachys, and that hyperdiverse regions such as Amazonia are probable arenas for ecological divergence in sympatry.

What can the phylogeny ofclass I KNOXgenes and their expression patterns in land plants tell us about the evolution of shoot development?

AbstractKNOX genes encode transcription factors (TFs), several of which act non-cell-autonomously. KNOX genes evolved in algae, and two classes, class I KNOX and class II KNOX genes, were already present in charophytes. In tracheophytes, class I KNOX genes are expressed in shoot apical meristems (SAMs) and thought to inhibit cell differentiation, whereas class II KNOX genes are expressed in mature organs regulating differentiation. In this review, we summarize the data available on gene families and expression patterns of class I and class II KNOX genes in embryophytes. The expression patterns of class I KNOX genes should be seen in the context of SAM structure and of leaf primordium development where the inhibition of cell differentiation needs to be lifted. Although the SAMs of angiosperms and gnetophytes almost always belong to the duplex type, several other types are distributed in gymnosperms, ferns, lycopods and bryophytes. KNOX gene families remained small (maximally five genes) in the representatives of bryophytes, lycopods and ferns examined thus far; however, they expanded to some extent in gymnosperms and, independently and much more strongly, in angiosperms. The growing sophistication of mechanisms to repress and re-induce class KNOX I expression played a major role in the evolution of leaf shape.

Fine mapping of the BnUC2 locus related to leaf up-curling and plant semi-dwarfing in Brassica napus

BackgroundStudies of leaf shape development and plant stature have made important contributions to the fields of plant breeding and developmental biology. The optimization of leaf morphology and plant height to improve lodging resistance and photosynthetic efficiency, increase planting density and yield, and facilitate mechanized harvesting is a desirable goal in Brassica napus.ResultsHere, we investigated a B. napus germplasm resource exhibiting up-curled leaves and a semi-dwarf stature. In progeny populations derived from NJAU5737 and Zhongshuang 11 (ZS11), we found that the up-curled leaf trait was controlled by a dominant locus, BnUC2. We then fine mapped the BnUC2 locus onto an 83.19-kb interval on chromosome A05 using single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) markers. We further determined that BnUC2 was a major plant height QTL that explained approximately 70% of the phenotypic variation in two BC5F3 family populations derived from NJAU5737 and ZS11. This result implies that BnUC2 was also responsible for the observed semi-dwarf stature. The fine mapping interval of BnUC2 contained five genes, two of which, BnaA05g16700D (BnaA05.IAA2) and BnaA05g16720D, were revealed by comparative sequencing to be mutated in NJAU5737. This result suggests that the candidate gene mutation (BnaA05g16700D, encoding Aux/IAA2 proteins) in the conserved Degron motif GWPPV (P63S) was responsible for the BnUC2 locus. In addition, investigation of agronomic traits in a segregated population indicated that plant height, main inflorescence length, and branching height were significantly reduced by BnUC2, whereas yield was not significantly altered. The determination of the photosynthetic efficiency showed that the BnUC2 locus was beneficial to improve the photosynthetic efficiency. Our findings may provide an effective foundation for plant type breeding in B. napus.ConclusionsUsing SNP and SSR markers, a dominant locus (BnUC2) related to up-curled leaves and semi-dwarf stature in B. napus has been fine mapped onto an 83.19-kb interval of chromosome A05 containing five genes. The BnaA05.IAA2 is inferred to be the candidate gene responsible for the BnUC2 locus.

Comparative transcriptome and co-expression analysis reveal key genes involved in leaf margin serration in Perilla frutescens

ObjectiveIn this study, we aimed to identify the genes involved in leaf margin serration in Perilla frutescens. P. frutescens (Family: Lamiaceae) is widely grown in Asian countries. Perilla leaf is the medicinal part stipulated in the Chinese Pharmacopoeia. There are mainly two types of perilla leaves: one with serrated leaf margin which is the phenotype described in the pharmacopoeia and the other with smooth leaf margin. MethodsTranscriptome sequencing, co-expression analysis, and qRT-PCR analysis of six perilla tissues sampled from two different phenotypes (serrated and smooth leaves) were performed. ResultsForty-three differentially expressed genes (DEGs), which may potentially regulate leaf shape, were identified through de novo transcriptome sequencing between the two groups. Genes involved in leaf shape regulation were identified. Simultaneously, we validated five DEGs by qRT-PCR, and the results were consistent with the transcriptome data. In addition, 1186 transcription factors (TFs) belonging to 45 TF families were identified. Moreover, the co-expression network of DEGs was constructed. ConclusionThe study identified the key genes that control leaf shape by comparing the transcriptomes. Our findings also provide basic data for further exploring P. frutescens, which can help study the mechanism of leaf shape development and molecular breeding.

Autoregulation of RCO by Low-Affinity Binding Modulates Cytokinin Action and Shapes Leaf Diversity.

Mechanisms through which the evolution of gene regulation causes morphological diversity are largely unclear. The tremendous shape variation among plant leaves offers attractive opportunities to address this question. In cruciferous plants, the REDUCED COMPLEXITY (RCO) homeodomain protein evolved via gene duplication and acquired a novel expression domain that contributed to leaf shape diversity. However, the molecular pathways through which RCO regulates leaf growth are unknown. A key question is to identify genome-wide transcriptional targets of RCO and the DNA sequences to which RCO binds. We investigate this question using Cardamine hirsuta, which has complex leaves, and its relative Arabidopsis thaliana, which evolved simple leaves through loss of RCO. We demonstrate that RCO directly regulates genes controlling homeostasis of the hormone cytokinin to repress growth at the leaf base. Elevating cytokinin signaling in the RCO expression domain is sufficient to both transform A.thaliana simple leaves into complex ones and partially bypass the requirement for RCO in C.hirsuta complex leaf development. We also identify RCO as its own target gene. RCO directly represses its own transcription via an array of low-affinity binding sites, which evolved after RCO duplicated from its progenitor sequence. This autorepression is required to limit RCO expression. Thus, evolution of low-affinity binding sites created a negative autoregulatory loop that facilitated leaf shape evolution by defining RCO expression and fine-tuning cytokinin activity. In summary, we identify a transcriptional mechanism through which conflicts between novelty and pleiotropy are resolved during evolution and lead to morphological differences between species.

Variability of morphometric characteristics of Betula pendula lamina under technogenic conditions of Dnipro city

The response of a plant organism to the effects of negative environmental factors, including the effects of multicomponent pollution, can be determined using a morphometric approach, setting the range of variability of biometric indicators of assimilation organs. The obtained data allow us to identify the directions of evolution of leaf shape and parameters under conditions of anthropogenic environment. The purpose of this work is to evaluate the variability of morphometric characteristics of lamina of Вetula pendula Roth. under technogenic conditions of the city of Dnipro. Leaf samples were collected in September – October 2018 at five test areas in the city of Dnipro (100 sheets each), which differed in the level of environmental pollution. For each leaf according to the method, five dimensions were measured on the left and right sides: width of the left and right halves of the leaf; the length of the vein of the second order, the second from the base of the leaf; the distance between the bases of the first and second veins of the second order; the distance between the ends of the first and second veins of the second order; the angle between the main vein and the second vein from the base of the leaf of the second order. It is shown that by the degree of increase of variation in the conditions of influence on the plants of B. pendula under conditions of multicomponent contamination of the environment the investigated signs of the lamina can be arranged as follows: 5 < 2 < 1 < 4 < 3. It is established that the most stable feature of the B. pendula lamina in the conditions of technogenesis is the angle between the main vein and the second vein from the base of the leaf of the second order, and the most variable one is the distance between the bases of the first and second veins of the second order. A tendency was found for the differences in the reactions of plants from the relatively clean area and contaminated territories: the control trees had a coefficient of variation higher for the right half of the leaf (right-sided asymmetry), whereas plants of the technogenic zones had left-sided asymmetry.

Fine mapping of an up-curling leaf locus (BnUC1) in Brassica napus

BackgroundLeaf shape development research is important because leaf shapes such as moderate curling can help to improve light energy utilization efficiency. Leaf growth and development includes initiation of the leaf primordia and polar differentiation of the proximal-distal, adaxial-abaxial, and centrolateral axes. Changes in leaf adaxial-abaxial polarity formation, auxin synthesis and signaling pathways, and development of sclerenchyma and cuticle can cause abnormal leaf shapes such as up-curling leaf. Although many genes related to leaf shape development have been reported, the detailed mechanism of leaf development is still unclear. Here, we report an up-curling leaf mutant plant from our Brassica napus germplasm. We studied its inheritance, mapped the up-curling leaf locus BnUC1, built near-isogenic lines for the Bnuc1 mutant, and evaluated the effect of the dominant leaf curl locus on leaf photosynthetic efficiency and agronomic traits.ResultsThe up-curling trait was controlled by one dominant locus in a progeny population derived from NJAU5734 and Zhongshuang 11 (ZS11). This BnUC1 locus was mapped in an interval of 2732.549 kb on the A05 chromosome of B. napus using Illumina Brassica 60 K Bead Chip Array. To fine map BnUC1, we designed 201 simple sequence repeat (SSR) primers covering the mapping interval. Among them, 16 polymorphic primers that narrowed the mapping interval to 54.8 kb were detected using a BC6F2 family population with 654 individuals. We found six annotated genes in the mapping interval using the B. napus reference genome, including BnaA05g18250D and BnaA05g18290D, which bioinformatics and gene expression analyses predicted may be responsible for leaf up-curling. The up-curling leaf trait had negative effects on the agronomic traits of 30 randomly selected individuals from the BC6F2 population. The near-isogenic line of the up-curling leaf (ZS11-UC1) was constructed to evaluate the effect of BnUC1 on photosynthetic efficiency. The results indicated that the up-curling leaf trait locus was beneficial to improve the photosynthetic efficiency.ConclusionsAn up-curling leaf mutant Bnuc1 was controlled by one dominant locus BnUC1. This locus had positive effects on photosynthetic efficiency, negative effects on some agronomic traits, and may help to increase planting density in B. napus.

Lamina shape does not correlate with lamina surface area: An analysis based on the simplified Gielis equation

The simplified Gielis equation (SGE) can approximately describe the leaf shapes of many different broad-leaved plant species by replacing two parameters of the SGE with leaf width and leaf length with a floating ratio (c–value) to adjust for leaf length. In this study, we tested the validity of the SGE in predicting leaf area using 20 bamboo species, 12 species of Rosaceae, 5 species of Lauraceae, and 5 species of Oleaceae. We find that c–values in leaf length for 20 bamboo species are all smaller than zero, whereas, for most tree species, c–values are larger than zero. Using c–values, there was a strong correlation (>0.99 for most of the species investigated) between actual and predicted leaf area. Also, using the SGE to fit the leaf profile data, the predicted leaf width approaches its actual value, whereas the predicted length is larger than or smaller than its actual value (for bamboo species and most tree species, respectively). Although c–values ranged from −15% to zero for bamboo species and from zero to 17% for tree species, the mean percent error in leaf area for most species did not exceed 5%. These findings indicate that leaves exhibit more variation in length than in width, i.e., leaf area is fairly conservative despite considerable variation in leaf shape. Given that the SGE adequately describes the areas of leaves with complex forms (e.g., several species of Rosaceae), our data indicate that the SGE is a useful tool for describing leaf morphometrics and may open a door for the study of leaf shape evolution.

A Growth-Based Framework for Leaf Shape Development and Diversity

SummaryHow do genes modify cellular growth to create morphological diversity? We study this problem in two related plants with differently shaped leaves: Arabidopsis thaliana (simple leaf shape) and Cardamine hirsuta (complex shape with leaflets). We use live imaging, modeling, and genetics to deconstruct these organ-level differences into their cell-level constituents: growth amount, direction, and differentiation. We show that leaf shape depends on the interplay of two growth modes: a conserved organ-wide growth mode that reflects differentiation; and a local, directional mode that involves the patterning of growth foci along the leaf edge. Shape diversity results from the distinct effects of two homeobox genes on these growth modes: SHOOTMERISTEMLESS broadens organ-wide growth relative to edge-patterning, enabling leaflet emergence, while REDUCED COMPLEXITY inhibits growth locally around emerging leaflets, accentuating shape differences created by patterning. We demonstrate the predictivity of our findings by reconstructing key features of C. hirsuta leaf morphology in A. thaliana.Video

Leaf area–length allometry and its implications in leaf shape evolution

According to Thompson’s principle of similarity, the area of an object should be proportional to its length squared. However, leaf area-length data of some plants have been demonstrated not to follow the principle of similarity. We explore the reasons why the leaf area-length allometry deviates from the principle of similarity and examine whether there is a general model describing the relationship among leaf area, width and length. We sampled more than 11,800 leaves from six classes of woody and herbaceous plants and tested the leaf area-length allometry. We compared six mathematical models based on root-mean-square error as the measure of goodness-of-fit. The best supported model described a proportional relationship between leaf area and the product of leaf width and length (i.e., the Montgomery model). We found that the extent to which the leaf area-length allometry deviates from the principle of similarity depends upon the extent of variation of the ratio of leaf width to length. Estimates of the parameter of the Montgomery model ranged between 1/2, which corresponds to a triangular leaf with leaf length as its height and leaf width as its base, and π/4, which corresponds to an elliptical leaf with leaf length as its major axis and leaf width as its minor axis, for the six classes of plants. The narrow range in practice of the Montgomery parameter implies an evolutionary stability for the leaf area of large-leaved plants despite the fact that leaf shapes of these plants are rather different.