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Leaves are determinate organs produced by the shoot apical meristem. Land plants demonstrate a large range of variation in leaf form. Here we discuss evolution of leaf form in the context of our current understanding of leaf development, as this has emerged from molecular genetic studies in model organisms. We also discuss specific examples where parallel studies of development in different species have helped understanding how diversification of leaf form may occur in nature.

• Background and Aims Diverse leaf forms in nature can be categorized into two groups: simple and compound. A simple leaf has a single blade unit, whilst a compound leaf is dissected into leaflets. For both simple and compound leaves, a MYB domain transcription factor PHANTASTICA (PHAN) plays an important role in establishing the adaxial domain in the leaf. Absence of PHAN in arabidopsis and antirrhinum leaves supresses blade development, and in tomato suppresses leaflet development. However, in the rachis and petiole regions of tomato leaves where PHAN and the adaxial domain coexist, it has been unclear why leaf blade and leaflets are not formed. We hypothesized that PHAN regulates the medio-lateral extent of the adaxial domain, thereby determining compound leaf architecture. • Methods To test this hypothesis, we generated and analysed transgenic tomato plants expressing tomato PHAN (SIPHAN) under the Cauliflower mosaic virus (CaMV) 35S promoter in both sense and antisense orientations, and tobacco plants that over-express tomato SlPHAN. • Key Results Modulations in SlPHAN resulted in a variety of leaf morphologies such as simple, ternate and compound in either a peltate or non-peltate arrangement. Measurements of the extent of the adaxial domain along the wild-type tomato leaf axis showed that the adaxial domain is narrowed in the rachis and petiole in comparison with regions where laminar tissue arises. In antiSlPHAN transgenic leaves, no blade or leaflet was formed where the adaxial domain was medio-laterally narrowed, and KNOX gene expression was correlatively upregulated. CaMV35S::SlPHAN expression led to widening of the adaxial domain and ectopie blade outgrowth in the rachis of tomato and in the petiole of tobacco. Taken together, these results suggest that SlPHAN plays a role in medio-lateral extension of the adaxial domain and contributes to final leaf morphology in tomato. • Conclusions This study provides a novel insight into leaf architecture in tomato and highlights how changes in the expression domain of a master regulator gene such as SlPHAN can be translated into diverse final leaf morphologies.

The mature morphology of most plants can usually be said to consist of three mutually exclusive organs: leaves, stems, and roots. The vast majority of mature morphologies may be easily grouped into one of these mutually exclusive categories. However, during very early stages of development and in many instances from inception, the division between organ categories becomes fuzzy due to the overlap in developmental processes that are shared between the aforementioned mutually exclusive categories. One such overlap has been described at the gene level where KNOXI homologues, transcription factors responsible for maintaining indeterminate cell fate, are expressed in the shoot apical meristem and during early stages of compound leaf development. This study characterizes the occurrence and spatial localization of mRNA of a KNOXI homologue, MaKN1, during the early stages of development in the simple leaves of Myriophyllum aquaticum, an aquatic angiosperm from the family Haloragaceae exhibiting pentamerous whorls of finely lobed leaves. A 300-bp KNOXI fragment was sequenced from M. aquaticum and used in an RNA localization study to determine the temporal and spatial expression of KNOXI during the early stages of leaf lobe development in M. aquaticum. The developmental sequence of leaves of M. aquaticum was also described using scanning electron microscopy. Lobe development of M. aquaticum occurs in two very distinct regions at the leaf base in an alternating fashion reminiscent of a distichous shoot system. It was discovered that MaKN1 expression is localized to both the shoot apical meristem and early stages of leaf primordia development (P1-P7). Initially, MaKN1 is expressed ubiquitously throughout primordia (P1-P3); however, as lobes develop, MaKN1 becomes localized to recently emerged lobe primordia, and disappears as lobes develop basipetally. The pattern of gene expression is indicative of shared developmental processes during early development between shoots, compound leaves, highly lobed simple leaves and unifoliate simple leaves which lack KNOXI expression. These findings are supportive of Arber's less rigid 'partial shoot' theory, which conceptualizes compound leaves as having shoot-like elements.

In angiosperms, leaf and stipule architectures are inherited species-specific traits. Variation in leaf and stipule sizes, and forms result from the interaction between abiotic and biotic stimuli, and gene regulatory network(s) that underlie the leaf and stipule developmental programme(s). Here, correspondence between variation in leaf and stipule architectures described for extant angiosperms and that induced mutationally and by imposition of stress in model angiosperm species, especially in Pisum sativum, was detected. Following inferences were drawn from the observations. (i) Several leaf forms in P. sativum have origin in fusion of stipule and leaf primordia. Perfoliate (and amplexicaul and connate) simple sessile leaves and sessile adnate leaves are the result of such primordial fusions. Reversal of changes in the gene regulatory network responsible for fusion products are thought to restore original stipule and leaf conditions. (ii) Compound leaf formation in several different model plants, is a result of promotion of pathways for such condition by gene regulatory networks directed by KNOX1 and LEAFY transcription factors or intercalation of the gene networks directed by them. (iii) Gene regulatory network for compound leaves in P. sativum when mutated generates highly complex compound leaves on one hand and simple leaves on other hand. These altered conditions are mutationally reversible. (vi) Simple leaves in model plants such as Arabidopsis thaliana despite overexpression of KNOX1 orthologues do not become compound. (v) All forms of leaves, including simple leaf, probably have origins in a gene regulatory network of the kind present in P. sativum.

The three major leaf types in chickpea are normal compound leaf, simple leaf and multipinnate. Simple leaf types are less commonly cultivated worldwide and are often reputed to be susceptible to ascochyta blight disease, whereas other leaf types range from resistant to susceptible. This study determined the association between host plant resistance to ascochyta blight and different leaf types in segregating populations derived from crosses between disease resistant and susceptible chickpea genotypes. In addition, the inheritance of disease resistance and leaf type was investigated in intraspecific progeny derived from crosses between two resistant genotypes with normal leaf type (ICC 3996 and Almaz), one susceptible simple leaf type (Kimberley Large) and one susceptible multipinnate leaf type (24 B-Isoline). Our results showed that, in these segregating populations, susceptibility to ascochyta blight was not linked to multipinnate or simple leaf types; resistance to ascochyta blight depended more on genetic background than leaf shape; leaf type was controlled by two genes with a dihybrid supplementary gene action; normal leaf type was dominant over other leaf types; and inheritance of ascochyta blight resistance was controlled by two major genes, one dominant and one recessive. Since there was no linkage between ascochyta blight susceptibility and leaf type, breeding various leaf types with ascochyta blight resistance is a clear possibility. These results have significant implications for chickpea improvement, as most current extra large seeded kabuli varieties have a simple leaf type.

In angiosperms, the relations between axis and leaves, as well as the general morphological structure of a leaf, follow a basic pattern which can be represented by two diagrams

Thanks to its ecological and geographical location, Turkey is the homeland of many fruit species and allows many fruit species to be grown. Hawthorn, which is understood to be important in human health and nutrition, is one of these fruit types. This study was carried out to identify morphological, biochemical, and molecular genetic variations of 22 hawthorn genotypes belonging to three different species collected from Kayseri province. The fruit (fruit length, fruit width, fruit weight, stone weight and soluble solid content) and leaf (leaf length, leaf width, petiole thickness) characteristics of the genotypes showed differences. Among the biochemical properties of the genotypes, the antioxidant activity, as % inhibition, ranged from 23.13 to 61.59%, the total flavonoid content ranged from 14.63 to 57.22 mg QE/100 g, and the total phenolic content ranged from 277.28 to 310.80 mg GAE/100 g. In the principal component analysis, species generally formed similar clusters. In molecular marker analysis, 101 bands were obtained from 13 ISSR (Inter Simple Sequence Repeats) primers. 76 of the bands were polymorphic and the polymorphism rate was calculated as 75.24%. The similarity index in the UPGMA (Unweighted Pair Group Method with Arithmetic Mean of Cluster analysis) dendogram because of the molecular analysis ranged between 0.71 and 0.88. In the dendrogram, genotypes did not show a dense clustering by species. The results obtained may benefit researchers in the determination and protection of genetic resources in breeding studies on hawthorn species.

Morphological leaf traits are frequently used to quantify, understand and predict plant and vegetation functional diversity and ecology, including environmental and climate change responses. Although morphological leaf traits are easy to measure, their coverage for characterising variation within species and across temporal scales is limited. At the same time, there are about 3100 herbaria worldwide, containing approximately 390 million plant specimens dating from the 16th to 21st century, which can potentially be used to extract morphological leaf traits. Globally, plant specimens are rapidly being digitised and images are made openly available via various biodiversity data platforms, such as iDigBio and GBIF. Based on a pilot study to identify the availability and appropriateness of herbarium specimen images for comprehensive trait data extraction, we developed a spatio-temporal dataset on intraspecific trait variability containing 128,036 morphological leaf trait measurements for seven selected species. After scrutinising the metadata of digitised herbarium specimen images available from iDigBio and GBIF (21.9 million and 31.6 million images for Tracheophyta ; accessed date December 2020), we identified approximately 10 million images potentially appropriate for our study. From the 10 million images, we selected seven species ( Salix bebbiana Sarg., Alnus incana (L.) Moench, Viola canina L., Salix glauca L., Chenopodium album L., Impatiens capensis Meerb. and Solanum dulcamara L.) , which have a simple leaf shape, are well represented in space and time and have high availability of specimens per species. We downloaded 17,383 images. Out of these, we discarded 5779 images due to quality issues. We used the remaining 11,604 images to measure the area, length, width and perimeter on 32,009 individual leaf blades using the semi-automated tool TraitEx. The resulting dataset contains 128,036 trait records. We demonstrate its comparability to trait data measured in natural environments following standard protocols by comparing trait values from the TRY database. We conclude that the herbarium specimens provide valuable information on leaf sizes. The dataset created in our study, by extracting leaf traits from the digitised herbarium specimen images of seven selected species, is a promising opportunity to improve ecological knowledge about the adaptation of size-related leaf traits to environmental changes in space and time.

Basmati is a premium quality rice, famous for its aroma, fine grain, and excellent cooking qualities. However, it is highly susceptible to bacterial leaf blight (BLB). To develop BLB resistant Basmati rice varieties, we transferred three (03) BLB resistance genes namely Xa4, xa5, Xa21 from a coarse yet BLB-resistant variety, IRBB57, developed by International Rice Research Institute into fine-quality rice variety, Super Basmati, through marker-assisted breeding. The background parent genome was recovered performing several backcrosses using Super Basmati as a recurrent parent to restore the bona fide Basmati character. The introgression of BLB resistance genes was followed by foreground selection using DNA-markers tightly linked with BLB resistance genes. The recovery of the Basmati parent genome (Background Selection) was determined using two different marker systems. Simple Sequence Repeats and Single Nucleotide Polymorphism. Several Super Basmati Introgressed (SBIL) lines with the individual as well as different BLB resistance gene combinations were developed. The stable representative SBILs from single, double, and triple gene combinations showing > 90% parent genome recovery were further studied for different attributes particularly to determine their degree of tolerance to the bacterial blight that was studied at two different locations—Philippines and Pakistan. We observed that SBILs carrying a combination of xa5 + Xa21 and Xa4 + xa5 + Xa21 conferred broad-scale resistance against both the highly virulent Pakistani and Philippines Xanthomonas oryzae pv. oryzae strains. The marker-aided background selection coupled with stringent phenotypic selection as well as foreground selection using DNA markers tightly linked with grain quality ensured that SBILs possess the bona fide Basmati character. The performance of key agronomic traits in selected SBILs was comparable with the recurrent parent with no significant agronomic or yield penalty associated with incorporation of the resistance genes, confirming the linkage drag has been minimized. Therefore, in addition to sustaining Basmati rice yield against BLB, the SBILs developed in this study may represent a useful resource for transferring resistance to BLB-susceptible rice varieties.

Many advanced satellite estimation methods have been developed, but global forest aboveground biomass (AGB) products remain largely uncertain. In this study, we explored data fusion techniques to generate a global forest AGB map for the 2000s at 0.01-degree resolution with improved accuracy by integrating ten existing local or global maps. The error removal and simple averaging algorithm, which is efficient and makes no assumption about the data and associated errors, was proposed to integrate these ten forest AGB maps. We first compiled the global reference AGB from in situ measurements and high-resolution AGB data that were originally derived from field data and airborne lidar data and determined the errors of each forest AGB map at the pixels with corresponding reference AGB values. Based on the errors determined from reference AGB data, the pixel-by-pixel errors associated with each of the ten AGB datasets were estimated from multiple predictors (e.g., leaf area index, forest canopy height, forest cover, land surface elevation, slope, temperature, and precipitation) using the random forest algorithm. The estimated pixel-by-pixel errors were then removed from the corresponding forest AGB datasets, and finally, global forest AGB maps were generated by combining the calibrated existing forest AGB datasets using the simple averaging algorithm. Cross-validation using reference AGB data showed that the accuracy of the fused global forest AGB map had an R-squared of 0.61 and a root mean square error (RMSE) of 53.68 Mg/ha, which is better than the reported accuracies (R-squared of 0.56 and RMSE larger than 80 Mg/ha) in the literature. Intercomparison with previous studies also suggested that the fused AGB estimates were much closer to the reference AGB values. This study attempted to integrate existing forest AGB datasets for generating a global forest AGB map with better accuracy and moved one step forward for our understanding of the global terrestrial carbon cycle by providing improved benchmarks of global forest carbon stocks.