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Biological shape diversity is often manifested in modulation of organ symmetry and modification of the patterned elaboration of repeated shape elements. 1,2,3,4,5 Whether and how these two aspects of shape determination are coordinately regulated is unclear. 5,6,7 Plant leaves provide an attractive system to investigate this problem, because they often show asymmetries along the proximodistal (PD) axis of their blades, along which they can also produce repeated marginal outgrowths such as serrations or leaflets. 1 One aspect of leaf shape diversity is heteroblasty, where the leaf form in a single genotype is modified with progressive plant age. 8,9,10,11 In Arabidopsis thaliana, a plant with simple leaves, SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 9 (SPL9) controls heteroblasty by activating CyclinD3 expression, thereby sustaining proliferative growth and retarding differentiation in adult leaves. 12,13 However, the precise significance of SPL9 action for leaf symmetry and marginal patterning is unknown. By combining genetics, quantitative shape analyses, and time-lapse imaging, we show that PD symmetry of the leaf blade in A. thaliana decreases in response to an age-dependent SPL9 expression gradient, and that SPL9 action coordinately regulates the distribution and shape of marginal serrations and overall leaf form. Using comparative analyses, we demonstrate that heteroblastic growth reprogramming in Cardamine hirsuta, a complex-leafed relative of A. thaliana, also involves prolonging the duration of cell proliferation and delaying differentiation. We further provide evidence that SPL9 enables species-specific action of homeobox genes that promote leaf complexity. In conclusion, we identified an age-dependent layer of organ PD growth regulation that modulates leaf symmetry and has enabled leaf shape diversification. [Display omitted] • An age-dependent growth gradient underpins regulation of A. thaliana leaf symmetry • SPL9-mediated heteroblastic growth control potentiates leaf histogenic capacity • Common growth patterns underlie heteroblasty in complex and simple leaves • SPL9 enables the action of homeobox genes that promote leaf complexity Li et al. study mechanisms underlying age-dependent changes in leaf symmetry and margin shape. They show that SPL9-mediated regulation of proliferative growth and differentiation along the leaf proximodistal axis modulates organ symmetry and marginal patterning and enables the action of homeobox genes that contributed to complex leaf shape evolution. [ABSTRACT FROM AUTHOR]

Abstract Alternative splicing (AS), a pivotal post-transcriptional regulatory mechanism, profoundly amplifies diversity and complexity of transcriptome and proteome. Liriodendron chinense (Hemsl.) Sarg., an excellent ornamental tree species renowned for its distinctive leaf shape, which resembles the mandarin jacket. Despite the documented potential genes related to leaf development of L. chinense, the underlying post-transcriptional regulatory mechanisms remain veiled. Here, we conducted a comprehensive analysis of the transcriptome to clarify the genome-wide landscape of the AS pattern and the spectrum of spliced isoforms during leaf developmental stages in L. chinense. Our investigation unveiled 50,259 AS events, involving 10,685 genes (32.9%), with intron retention as the most prevalent events. Notably, the initial stage of leaf development witnessed the detection of 804 differentially AS events affiliated with 548 genes. Although both differentially alternative splicing genes (DASGs) and differentially expressed genes (DEGs) were enriched into morphogenetic related pathways during the transition from fishhook (P2) to lobed (P7) leaves, there was only a modest degree of overlap between DASGs and DEGs. Furthermore, we conducted a comprehensively AS analysis on homologous genes involved in leaf morphogenesis, and most of which are subject to post-transcriptional regulation of AS. Among them, the AINTEGUMENTA-LIKE transcript factor LcAIL5 was characterization in detailed, which experiences skipping exon (SE), and two transcripts displayed disparate expression patterns across multiple stages. Overall, these findings yield a comprehensive understanding of leaf development regulation via AS, offering a novel perspective for further deciphering the mechanism of plant leaf morphogenesis.

Alternative splicing (AS), a pivotal post-transcriptional regulatory mechanism, profoundly amplifies diversity and complexity of transcriptome and proteome. Liriodendron chinense (Hemsl.) Sarg., an excellent ornamental tree species renowned for its distinctive leaf shape, which resembles the mandarin jacket. Despite the documented potential genes related to leaf development of L. chinense, the underlying post-transcriptional regulatory mechanisms remain veiled. Here, we conducted a comprehensive analysis of the transcriptome to clarify the genome-wide landscape of the AS pattern and the spectrum of spliced isoforms during leaf developmental stages in L. chinense. Our investigation unveiled 50,259 AS events, involving 10,685 genes (32.9%), with intron retention as the most prevalent events. Notably, the initial stage of leaf development witnessed the detection of 804 differentially AS events affiliated with 548 genes. Although both differentially alternative splicing genes (DASGs) and differentially expressed genes (DEGs) were enriched into morphogenetic related pathways during the transition from fishhook (P2) to lobed (P7) leaves, there was only a modest degree of overlap between DASGs and DEGs. Furthermore, we conducted a comprehensively AS analysis on homologous genes involved in leaf morphogenesis, and most of which are subject to post-transcriptional regulation of AS. Among them, the AINTEGUMENTA-LIKE transcript factor LcAIL5 was characterization in detailed, which experiences skipping exon (SE), and two transcripts displayed disparate expression patterns across multiple stages. Overall, these findings yield a comprehensive understanding of leaf development regulation via AS, offering a novel perspective for further deciphering the mechanism of plant leaf morphogenesis. [ABSTRACT FROM AUTHOR]

Auxin plays an essential role in modulating leaf development. However, its role in leaf development in rice (Oryza sativa L.) remains largely unknown. In this study, we found that PINOID (OsPID) and two Sister-of-PIN1s, termed PIN-FORMED1c (OsPIN1c) and OsPIN1d, are necessary for rice leaf development. The ospin1c ospin1d null mutant lines presented severe defects in leaf morphogenesis, including drooping and semi-drooping blades, an abnormally thickened sheath and lamina joint, and fused leaves with absent ligules and auricles. Loss-of-function ospid mutants displayed generally similar leaf morphology but lacked leaf fusion. Interestingly, misshaped leaf genesis displayed a preference for being ipsilateral. In addition, OsPIN1c and OsPID were commonly localized in the initiating leaf primordia. Furthermore, accompanied by the more severe organ morphogenesis in the ospin1c ospin1d ospid triple mutant, RNA sequencing analysis revealed that many genes essential for leaf development have an altered expression level. Together, this study furthers our understanding of the role auxin transport plays during leaf development in monocot rice. [ABSTRACT FROM AUTHOR]

The chloroplast is a semi-autonomous organelle with a double membrane structure, and its structural stability is a prerequisite for its correct function. Chloroplast development is regulated by known nuclear-encoded chloroplast proteins or proteins encoded within the chloroplast itself. However, the mechanism of chloroplast development regulated by other organelles remains largely unknown. Here, we report that the nuclear-localized DEAD-box RNA helicase 13 (RH13) is essential for chloroplast development in Arabidopsis thaliana. RH13 is widely expressed in tissues and localized to the nucleolus. A homozygous rh13 mutant shows abnormal chloroplast structure and leaf morphogenesis. Proteomic analysis showed that the expression levels of photosynthesis-related proteins in chloroplasts were reduced due to loss of RH13. Furthermore, RNA-sequencing and proteomics data revealed decreases in the expression levels of these chloroplast-related genes, which undergo alternative splicing events in the rh13 mutant. Taken together, we propose that nucleolus-localized RH13 is critical for chloroplast development in Arabidopsis. [ABSTRACT FROM AUTHOR]

Plant leaves display abundant morphological richness yet grow to characteristic sizes and shapes. Beginning with a small number of undifferentiated founder cells, leaves evolve via a complex interplay of regulatory factors that ultimately influence cell proliferation and subsequent post-mitotic cell enlargement. During their development, a sequence of key events that shape leaves is both robustly executed spatiotemporally following a genomic molecular network and flexibly tuned by a variety of environmental stimuli. Decades of work on Arabidopsis thaliana have revisited the compensatory phenomena that might reflect a general and primary size-regulatory mechanism in leaves. This review focuses on key molecular and cellular events behind the organ-wide scale regulation of compensatory mechanisms. Lastly, emerging novel mechanisms of metabolic and hormonal regulation are discussed, based on recent advances in the field that have provided insights into, among other phenomena, leaf-size regulation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

AINTEGUMENTA-LIKE (AIL) transcription factors are widely studied and play crucial roles in plant growth and development. However, the functions of the AIL family in legume species are largely unknown. In this study, 11 MtAIL genes were identified in the model legume Medicago truncatula, of which four of them are MtANTs. In situ analysis showed that MtANT1 was highly expressed in the shoot apical meristem (SAM) and leaf primordium. Characterization of mtant1 mtant2 mtant3 mtant4 quadruple mutants and MtANT1-overexpressing plants revealed that MtANTs were not only necessary but also sufficient for the regulation of leaf size, and indicated that they mainly function in the regulation of cell proliferation during secondary morphogenesis of leaves in M. truncatula. This study systematically analyzed the MtAIL family at the genome-wide level and revealed the functions of MtANTs in leaf growth. Thus, these genes may provide a potential application for promoting the biomass of legume forages. [ABSTRACT FROM AUTHOR]

Excess PPi triggers developmental defects in a cell-autonomous manner. The level of inorganic pyrophosphate (PPi) must be tightly regulated in all kingdoms for the proper execution of cellular functions. In plants, the vacuolar proton pyrophosphatase (HC-PPase) has a pivotal role in PPi homeostasis. We previously demonstrated that the excess cytosolic PPi in the HC-PPase loss-of-function fugu5 mutant inhibits gluconeogenesis from seed storage lipids, arrests cell division in cotyledonary palisade tissue, and triggers a compensated cell enlargement (CCE). Moreover, PPi alters pavement cell (PC) shape, stomatal patterning, and functioning, supporting specific yet broad inhibitory effects of PPi on leaf morphogenesis. Whereas these developmental defects were totally rescued by the expression of the yeast soluble pyrophosphatase IPP1, sucrose supply alone canceled CCE in the palisade tissue but not the epidermal developmental defects. Hence, we postulated that the latter are likely triggered by excess PPi rather than a sucrose deficit. To formally test this hypothesis, we adopted a spatiotemporal approach by constructing and analyzing fugu5-1 PDF1pro::IPP1, fugu5-1 CLV1pro::IPP1, and fugu5-1 ICLpro::IPP1, whereby PPi was removed specifically from the epidermis, palisade tissue cells, or during the 4 days following seed imbibition, respectively. It is important to note that whereas PC defects in fugu5-1 PDF1pro::IPP1 were completely recovered, those in fugu5-1 CLV1pro::IPP1 were not. In addition, phenotypic analyses of fugu5-1 ICLpro::IPP1 lines demonstrated that the immediate removal of PPi after seed imbibition markedly improved overall plant growth, abolished CCE, but only partially restored the epidermal developmental defects. Next, the impact of spatial and temporal removal of PPi was investigated by capillary electrophoresis time-of-flight mass spectrometry (CE-TOF MS). Our analysis revealed that the metabolic profiles are differentially affected among all the above transgenic lines, and consistent with an axial role of central metabolism of gluconeogenesis in CCE. Taken together, this study provides a conceptual framework to unveil metabolic fluctuations within leaf tissues with high spatio-temporal resolution. Finally, our findings suggest that excess PPi exerts its inhibitory effect in planta in the early stages of seedling establishment in a tissue- and cell-autonomous manner. [ABSTRACT FROM AUTHOR]

Plants produce a rich diversity of biological forms, and the diversity of leaves is especially notable. Mechanisms of leaf morphogenesis have been studied in the past two decades, with a growing focus on the interactive roles of mechanics in recent years. Growth of plant organs involves feedback by mechanical stress: growth induces stress, and stress affects growth and morphogenesis. Although much attention has been given to potential stress-sensing mechanisms and cellular responses, the mechanical principles guiding morphogenesis have not been well understood. Here we synthesize the overarching roles of mechanics and mechanical stress in multilevel and multiple stages of leaf morphogenesis, encompassing leaf primordium initiation, phyllotaxis and venation patterning, and the establishment of complex mature leaf shapes. Moreover, the roles of mechanics at multiscale levels, from subcellular cytoskeletal molecules to single cells to tissues at the organ scale, are articulated. By highlighting the role of mechanical buckling in the formation of three-dimensional leaf shapes, this review integrates the perspectives of mechanics and biology to provide broader insights into the mechanobiology of leaf morphogenesis. Mechanical regulation of plant growth is rapidly gaining the interest of researchers. This review details how mechanics takes part in leaf morphogenesis during the initiation of leaf primordia, emergence of phyllotaxis patterns, and development of complex leaf shapes. By highlighting the role of mechanical buckling in leaf shape formation, this review integrates perspectives of mechanics and biology to provide insights into plant mechanobiology. [ABSTRACT FROM AUTHOR]

Leaf morphogenesis requires precise regulation of gene expression to achieve organ separation and flat-leaf form. The poplar KNOTTED-like homeobox gene PagKNAT2/6b could change plant architecture, especially leaf shape, in response to drought stress. However, its regulatory mechanism in leaf development remains unclear. In this work, gene expression analyses of PagKNAT2/6b suggested that PagKNAT2/6b was highly expressed during leaf development. Moreover, the leaf shape changes along the adaxial-abaxial, medial-lateral, and proximal-distal axes caused by the mis-expression of PagKNAT2/6b demonstrated that its overexpression (PagKNAT2/6b OE) and SRDX dominant repression (PagKNAT2/6b SRDX) poplars had an impact on the leaf axial development. The crinkle leaf of PagKNAT2/6b OE was consistent with the differential expression gene PagBOP1/2a (BLADE-ON-PETIOLE), which was the critical gene for regulating leaf development. Further study showed that PagBOP1/2a was directly activated by PagKNAT2/6b through a novel cis-acting element "CTCTT". Together, the PagKNAT2/6b-PagBOP1/2a module regulates poplar leaf morphology by affecting axial development, which provides insights aimed at leaf shape modification for further improving the drought tolerance of woody plants. [ABSTRACT FROM AUTHOR]

The above-ground organs in plants display a rich diversity, yet they grow to characteristic sizes and shapes. Organ morphogenesis progresses through a sequence of key events, which are robustly executed spatiotemporally as an emerging property of intrinsic molecular networks while adapting to various environmental cues. This Review focuses on the multiscale control of leaf morphogenesis. Beyond the list of known genetic determinants underlying leaf growth and shape, we focus instead on the emerging novel mechanisms of metabolic and biomechanical regulations that coordinate plant cell growth non-cell-autonomously. This reveals how metabolism and mechanics are not solely passive outcomes of genetic regulation but play instructive roles in leaf morphogenesis. Such an integrative view also extends to fluctuating environmental cues and evolutionary adaptation. This synthesis calls for a more balanced view on morphogenesis, where shapes are considered from the standpoints of geometry, genetics, energy and mechanics, and as emerging properties of the cellular expression of these different properties. [ABSTRACT FROM AUTHOR]

Leaf morphogenesis in Vitis vinifera is closely associated with the biosynthesis of various metabolites, starch, and growth-related molecules. In the present study, Illumina RNA deep sequencing-based on transcriptome analysis was deployed to understand leaf morphogenesis in Vitis vinifera. The KEGG pathway analysis revealed the transcripts involved in the biosynthesis of major metabolites leading to leaf growth. The highest number of DEGs were down-regulated at young leave-vs-mature leaves stages (3,501) followed by large leaves-vs-mature leaves (2,364); however, the minimum number of up-regulated transcripts were recorded at young leaves-vs-immature leaves (195). The gene regulation in the starch biosynthetic pathway, young leaves-vs-mature leaves showed the highest number of transcripts (24 up-regulated and 60 down-regulated). For ABC Transporters, 224 transcripts were expressed, among which the maximum number of transcripts (59) were recorded in large leaves-vs-mature leaves. Amino and nucleotide sugar metabolism showed 112 transcripts (22 up-regulated and 90 down-regulated), in which immature leaves-vs-mature leaves expressed 30 DEGs. In addition, Flavonoid pathway showed the highest number of transcripts i.e. 903 were expressed among the studied pathways. The findings of this study will also help to a better understanding of the underlying process during grape leaf morphogenesis and to unravel the mechanism. [ABSTRACT FROM AUTHOR]

An ideal leaf shape is beneficial to the yield of rice. Molecular understanding of the leaf primordia and polarity establishment plays a significant role in exploring the genetic regulatory network of leaf morphogenesis. In recent years, researchers have cloned an array of coding genes and a few non-coding small RNAs involved in rice leaf development through regulating the development of leaf primordia, vascular bundles, sclerenchyma cells, bulliform cells, cell walls and epidermis cells. These genes and their interactions play critical roles in rice leaf development through the determination and regulatory role in gene expression, and their coordination with other genetic networks or signal pathways. But the relationship among these genes is poorly defined and the underlying network is still unclear. In this review, we introduced the regulatory pathways of leaf primordium development and leaf polarity establishment, mainly the relationship between cell development mechanism and leaf polarity establishment, focusing on how leaf tissue affects leaf shape. Hopefully, the regulation network reviewed here has immediate implications for future research and genomic design breeding.

TEOSINTE BRANCHED 1/CYCLOIDEA/PROLIFERATING CELL FACTOR 1 (TCP) transcription factors control multiple aspects of growth and development in various plant species. However, few genes were reported to be directly targeted and regulated by them through their specific binding sites, and then uncover their functions in plants. A consensus DNA-binding site motif of TCP2 was identified by random binding site selection (RBSS). DNA recognized by TCP2 contained the motif G(G/T)GGNCC(A/C), which showed high consistency with motifs bound by other TCP domain proteins. Consequently, this motif was regarded as the specific DNA-binding sites of TCP2. Circadian clock associated 1 (CCA1) and EARLY FLOWERING 3 (ELF3) were subsequently considered as potential target genes owing to the containing of the similar TCP2 binding sites or core binding sites GGNCC and found to be positively regulated by TCP2 via DNA binding. Phenotype analysis results showed that mutation and over-expression of TCP2 resulted in variations in leaf morphogenesis, especially the double or triple mutations of TCP2, 4 and 10. Mutations in TCPs caused late flowering. Finally, TCP2 was shown to influence hypocotyl elongation by mediating the jasmonate signaling pathway. Overall, these results provide a basis for future studies aimed at distinguishing the target genes of TCP2 and elucidating the important roles of TCP2 in plant growth and development. [ABSTRACT FROM AUTHOR]

Leaf morphogenesis requires precise regulation of gene expression to achieve organ separation and flat-leaf form. The poplar KNOTTED-like homeobox gene PagKNAT2/6b could change plant architecture, especially leaf shape, in response to drought stress. However, its regulatory mechanism in leaf development remains unclear. In this work, gene expression analyses of PagKNAT2/6b suggested that PagKNAT2/6b was highly expressed during leaf development. Moreover, the leaf shape changes along the adaxial-abaxial, medial-lateral, and proximal-distal axes caused by the mis-expression of PagKNAT2/6b demonstrated that its overexpression (PagKNAT2/6b OE) and SRDX dominant repression (PagKNAT2/6b SRDX) poplars had an impact on the leaf axial development. The crinkle leaf of PagKNAT2/6b OE was consistent with the differential expression gene PagBOP1/2a (BLADE-ON-PETIOLE), which was the critical gene for regulating leaf development. Further study showed that PagBOP1/2a was directly activated by PagKNAT2/6b through a novel cis-acting element “CTCTT”. Together, the PagKNAT2/6b-PagBOP1/2a module regulates poplar leaf morphology by affecting axial development, which provides insights aimed at leaf shape modification for further improving the drought tolerance of woody plants.

Summary: The biosynthesis and modification of cell wall composition and structure are controlled by hundreds of enzymes and have a direct consequence on plant growth and development. However, the majority of these enzymes has not been functionally characterised.Rice mutants with leaf‐rolling phenotypes were screened in a field. Phenotypic analysis under controlled conditions was performed for the selected mutant and the relevant gene was identified by map‐based cloning. Cell wall composition was analysed by glycome profiling assay.We identified a photo‐sensitive leaf rolling 1 (psl1) mutant with 'napping' (midday depression of photosynthesis) phenotype and reduced growth. The PSL1 gene encodes a cell wall‐localised polygalacturonase (PG), a pectin‐degrading enzyme. psl1 with a 260‐bp deletion in its gene displayed leaf rolling in response to high light intensity and/or low humidity. Biochemical assays revealed PG activity of recombinant PSL1 protein. Significant modifications to cell wall composition in the psl1 mutant compared with the wild‐type plants were identified. Such modifications enhanced drought tolerance of the mutant plants by reducing water loss under osmotic stress and drought conditions.Taken together, PSL1 functions as a PG that modifies cell wall biosynthesis, plant development and drought tolerance in rice. [ABSTRACT FROM AUTHOR]

Plant cells cultivated in vitro are a convenient model for studying the genetic and physiological mechanisms necessary for the cells to acquire a state of pluripotency. Earlier studies on a model plant Arabidopsis thaliana (L.) Heynh. have identified the key role of genes that determine the pluripotency of cells in the shoot apical meristem in de novo shoot regeneration in tissue culture. In accordance with this, cells of mutant plants with a higher level of expression of pluripotency genes were characterized by an increased potential for de novo shoot regeneration. The tae mutant was the exception to this rule. The mutant resumed the expression of pluripotency genes and cell proliferation at the late stages of leaf development, which indicates a violation of the mechanisms for maintaining epigenetic cellular memory. At the same time, leaf cells cultured in vitro showed a lower proliferative activity compared to the wild type and were not capable of de novo regeneration of shoots. A decrease in the regenerative potential of cultured cells of the tae mutant indicates an important role of epigenetic memory in the response of cells to exogenous hormones. Impaired epigenetic memory of leaf cells of the tae mutant and differences in their proliferative and regenerative capacities in planta and in vitro make this mutant a unique model for studying the role of epigenetic modifications in the regulation of cell pluripotency. [ABSTRACT FROM AUTHOR]

An ideal leaf shape is beneficial to the yield of rice. Molecular understanding of the leaf primordia and polarity establishment plays a significant role in exploring the genetic regulatory network of leaf morphogenesis. In recent years, researchers have cloned an array of coding genes and a few non-coding small RNAs involved in rice leaf development through regulating the development of leaf primordia, vascular bundles, sclerenchyma cells, bulliform cells, cell walls and epidermis cells. These genes and their interactions play critical roles in rice leaf development through the determination and regulatory role in gene expression, and their coordination with other genetic networks or signal pathways. But the relationship among these genes is poorly defined and the underlying network is still unclear. In this review, we introduced the regulatory pathways of leaf primordium development and leaf polarity establishment, mainly the relationship between cell development mechanism and leaf polarity establishment, focusing on how leaf tissue affects leaf shape. Hopefully, the regulation network reviewed here has immediate implications for future research and genomic design breeding. [ABSTRACT FROM AUTHOR]

SUMMARY: In cultivated grasses, tillering, spike architecture and seed shattering represent major agronomical traits. In barley, maize and rice, the NOOT‐BOP‐COCH‐LIKE (NBCL) genes play important roles in development, especially in ligule development, tillering and flower identity. However, compared with dicots, the role of grass NBCL genes is underinvestigated. To better understand the role of grass NBCLs and to overcome any effects of domestication that might conceal their original functions, we studied TILLING nbcl mutants in the non‐domesticated grass Brachypodium distachyon. In B. distachyon, the NBCL genes BdUNICULME4 (CUL4) and BdLAXATUM‐A (LAXA) are orthologous, respectively, to the barley HvUniculme4 and HvLaxatum‐a, to the maize Zmtassels replace upper ears1 and Zmtassels replace upper ears2 and to the rice OsBLADE‐ON‐PETIOLE1 and OsBLADE‐ON‐PETIOLE2/3. In B. distachyon, our reverse genetics study shows that CUL4 is not essential for the establishment of the blade–sheath boundary but is necessary for the development of the ligule and auricles. We report that CUL4 also exerts a positive role in tillering and a negative role in spikelet meristem activity. On the other hand, we demonstrate that LAXA plays a negative role in tillering, positively participates in spikelet development and contributes to the control of floral organ number and identity. In this work, we functionally characterized two new NBCL genes in a context of non‐domesticated grass and highlighted original roles for grass NBCL genes that are related to important agronomical traits. Significance Statement: Loss of function of BdUNICULME4 reduces tillering, alters ligule and auricle development and increases spikelet meristem activity. Mutation of BdLAXATUM‐A increases tillering, affects spikelet architecture and disturbs floral organization. [ABSTRACT FROM AUTHOR]

Populus euphratica Oliv. has typical heterophylly. Linear, lanceolate, ovate and broad-ovate leaves appeared in turn from sprouting to development, to maturity. The environmental adaptabilities of P. euphraticas with different leaves were also different. To explore the role of circRNAs on the morphogenesis of P. euphratica heteromorphic leaves (P.hl) and their stress response, the expression profile of circRNAs was analyzed by strand-specific RNA sequencing for the above four kinds of heteromorphic leaves. According to ceRNA hypothesis, 18 differentially expressed cirRNAs (DECs) could influence the expression of 84 mRNAs by antagonizing 23 miRNAs in five sample-pairs. Based on the function of 84 mRNAs, these DECs participate in development process, response to stimulus, response to hormonal et al. Therefore, these circRNAs were involved in the P. hl morphogenesis and stress response by interacting with miRNAs and mRNAs. Our study complemented the genebank of P. euphratica and provided a new strategy for studying leaf development. • The desert plant P. euphratica has typical heterophylly. • The molecular mechanism of the morphogenesis of P. euphratica heteromorphic leaves (P.hl) is still unclear. • CircRNAs were identified for the first time in P.hl. • CircRNAs of P.hl were involved in the P.hl morphogenesis and stress response by interacting with miRNAs and mRNAs. [ABSTRACT FROM AUTHOR]

How is time encoded into organ growth and morphogenesis? We address this question by investigating heteroblasty, where leaf development and form are modified with progressing plant age. By combining morphometric analyses, fate-mapping through live-imaging, computational analyses, and genetics, we identify age-dependent changes in cell-cycle-associated growth and histogenesis that underpin leaf heteroblasty. We show that in juvenile leaves, cell proliferation competence is rapidly released in a "proliferation burst" coupled with fast growth, whereas in adult leaves, proliferative growth is sustained for longer and at a slower rate. These effects are mediated by the SPL9 transcription factor in response to inputs from both shoot age and individual leaf maturation along the proximodistal axis. SPL9 acts by activating CyclinD3 family genes, which are sufficient to bypass the requirement for SPL9 in the control of leaf shape and in heteroblastic reprogramming of cellular growth. In conclusion, we have identified a mechanism that bridges across cell, tissue, and whole-organism scales by linking cell-cycle-associated growth control to age-dependent changes in organ geometry. [Display omitted] • Time-lapse and fate maps yield a cellular growth framework for leaf heteroblasty • A default "cell proliferation burst" underpins juvenile leaf morphogenesis • SPL9 maintains proliferative growth along an age-dependent proximodistal gradient • SPL9-CYCD3 transcriptional module times leaf development via cell cycle control Li et al. study cellular growth reprogramming underlying heteroblastic changes in leaf form. They show that an SPL9-CYCD3 transcriptional module encodes developmental time into leaf morphogenesis by timing cell proliferation and growth, thus orchestrating plant development across temporal scales, from the cell cycle to age-dependent organ form. [ABSTRACT FROM AUTHOR]

Plants employ cell-surface receptor-like kinases to detect extrinsic and intrinsic signals, thus make a trade-off between growth and immunity. The receptor-like cytoplasmic kinases on the cytoplasmic side act as downstream components involved in the activation, transmission, and integration of intracellular signals. In Arabidopsis thaliana, the RLCK BOTRYTIS-INDUCED KINASE1 (BIK1) associates with multiple RLKs to regulate pathogen defense responses and brassinosteroid (BR) signaling. However, little is known about the biological functions of BIK1 in developmental processes in Arabidopsis. In this study, we established that mutation of ERECTA (ER), an important RLK, counteracts the developmental effects of loss of BIK1 function. BIK1 and ER play opposing roles in leaf morphogenesis and inflorescence architecture. Moreover, we confirmed that BIK1 is required to maintain appropriate auxin response during leaf margin morphogenesis. Finally, we found that BIK1 interacts with ER-family proteins and directly phosphorylates ER. Our findings might provide novel insight into the function of BIK1 in leaf and inflorescence development.

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.

Plants are exposed to numerous biotic and abiotic stresses, and light is one of the most important factors that influences the plant morphology. This study was carried out to examine how the lighting direction affected the plant morphology by investigating the growth parameters, epidermal cell elongation, stomatal properties, and physiological changes. Seedlings of two head lettuce (Lactuca sativa L.) cultivars, Caesar Green and Polla, were subjected to a 12 h photoperiod with a 300 μmol·m−2·s−1 photosynthetic photon flux density (PPFD) provided by light emitting diodes (LEDs) from three directions: the top, side, and bottom, relative to the plants. Compared with the top and side lighting, the bottom lighting increased the leaf angle and canopy by stimulating the epidermal cell elongation in leaf midrib, reduced the leaf number and root biomass, and induced large stomata with a low density, which is associated with reduced stomatal conductance and carbohydrate contents. However, the proline content and quantum yield exhibited no significant differences with the different lighting directions in both cultivars, which implies that the plants were under normal physiological conditions. In a conclusion, the lighting direction had a profound effect on the morphological characteristics of lettuce, where the plants adapted to the changing lighting environments.

Plants employ cell-surface receptor-like kinases to detect extrinsic and intrinsic signals, thus make a trade-off between growth and immunity. The receptor-like cytoplasmic kinases on the cytoplasmic side act as downstream components involved in the activation, transmission, and integration of intracellular signals. In Arabidopsis thaliana , the RLCK BOTRYTIS-INDUCED KINASE1 (BIK1) associates with multiple RLKs to regulate pathogen defense responses and brassinosteroid (BR) signaling. However, little is known about the biological functions of BIK1 in developmental processes in Arabidopsis. In this study, we established that mutation of ERECTA (ER), an important RLK, counteracts the developmental effects of loss of BIK1 function. BIK1 and ER play opposing roles in leaf morphogenesis and inflorescence architecture. Moreover, we confirmed that BIK1 is required to maintain appropriate auxin response during leaf margin morphogenesis. Finally, we found that BIK1 interacts with ER-family proteins and directly phosphorylates ER. Our findings might provide novel insight into the function of BIK1 in leaf and inflorescence development. [ABSTRACT FROM AUTHOR]

Herbivores target young leaves in forests world‐wide. How this strong and predictable selection pressure has shaped plant defence syndromes remains unclear. Specifically, whether young leaf herbivory has led to general global patterns of shifting leaf defences during leaf development (i.e. ontogenetic trajectories) remains unknown but likely.Using meta‐analysis, we have synthesized developmental shifts in chemical, physical and indirect defence traits, as well as leaf nutrient content, during leaf expansion and maturation across 124 woody plant species. Leaf traits were compared for immature young leaves vs. mature leaves within studies, and these developmental shifts were then compared across studies to characterize general patterns.Traits shifted strongly during leaf maturation, giving rise to discrete defence syndromes, with young leaves having significantly greater nutrient and secondary chemistry concentrations but reduced toughness and indirect defence traits than mature leaves. These patterns corroborate a growing consensus on the importance of ontogeny in plant defences, illustrating ontogenetic trajectories at the scale of leaves.Trait developmental shifts were stronger in species with synchronous than asynchronous leaf flushing, but whether this reflects variation across biomes remains unclear.Future research on under‐studied traits, such as alkaloids, cyanogenesis, leaf phosphorus content and indirect defence traits, and in a more biogeographic context will provide additional insights into the generality of shifts in defence syndromes during leaf development. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Auxin is an important inductor of organogenesis. During leaf development, local sites with high auxin concentration initiate the formation of leaf primordia and venation, control the growth of lamina and lamina margin development. The proliferative activity of the leaf cells of the Arabidopsis thalianataeniata (tae) mutant and the role of auxin in the development of the ectopic secondary margins and lobes on the leaf of the mutant were analyzed in the study. It has been established that, in addition to the ability for ectopic proliferation of leaf cells, the tae mutant demonstrates a complex of traits characteristic of plants with impaired auxin transport. It was shown that a mutation in the PID gene, which disrupts the polar auxin transport, causes the suppression of ectopic outgrowths on the leaf of the tae mutant. These data indicate the important role of auxin transport in maintaining the leaf cell pluripotency and the development of lobes on the leaf of the tae mutant. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Leaf adaxial–abaxial polar establishment is crucial for leaf morphogenesis. • A novel leaf morphological mutant crsl with curled rod-shaped leaves and strikingly altered leaf adaxial–abaxial development was identified in Chinese cabbage. • BraA02g016100.3C (BrCRSL) gene is homologous to Arabidopsis MAB1 and encodes a putative mitochondrial PDH E1β subunit protein, which is the most likely causal gene for crsl and might serve as a new regulator of leaf polarity specification. • It's the first to identify BrCRSL function in leaf morphogenesis. Leaf morphogenesis requires precise genetic control and hormone regulation to develop into ideal plant architectures. Leaf flattening is an adaptive trait to obtain efficient photosynthesis, for which the leaf adaxial–abaxial polar establishment is of great importance. Herein, a novel leaf morphological mutant, curled rod-shaped leaf (crsl), was isolated and characterized from Chinese cabbage (Brassica rapa L. ssp. pekinensis) EMS-induced population. The leaves in crsl were slender and rod-shaped, with the abaxial side folded upwards and the distal side curled downwards, the mesophyll cells were loosely arranged, and the epidermal morphology was opposite on the adaxial and abaxial surface. Genetic analysis revealed that the curled rod-shaped leaf mutant phenotype was controlled by a dominate nuclear gene, named BrCRSL. MutMap and Kompetitive Allele Specifc PCR (KASP) genotyping demonstrated that BraA02g016100.3C was the most likely candidate for BrCRSL. Compared with the wild-type, a non-synonymous SNP mutation (C to T) occurred in the 8th exon of BraA02g016100.3C in crsl. BraA02g016100.3C is orthologous of Arabidopsis thaliana MAB1 (AT5G50850), which encodes a putative mitochondrial PDH E1β subunit protein and contributes to PIN-dependent auxin transport in organ development. The amino acid substitution from proline (P) to leucine (L) is conserved among the homologous proteins of BraA02g016100.3C. ​The crsl mutant exhibited abnormal auxin metabolism, primarily manifested by high level of L-tryptophan (TRP) accumulation that is the precursor of IAA biosynthesis. Furthermore, the expression of a wide range of leaf adaxial/abaxial polarity-related genes was affected in crsl. Our results contribute to a better understanding of the genetic control mechanism underlying leaf morphogenesis in Chinese cabbage and provide new insights into the auxin-related leaf axial growth. [ABSTRACT FROM AUTHOR]

The aim of this study was to quantify the relative importance of leaf age and leaf length on the dynamics of neutral detergent fibre (NDF), and 24-h in vitro digestibility of NDF (NDFD) and dry matter (DMD) of tall fescue (Lolium arundinaceum (Schreb) Darbysh.). Mini-swards were conditioned and used to conduct two experiments, the first with 4-cm plant stubble height in spring-summer 2009 and autumn-winter 2011, and the second with 4-cm or 10-cm plant stubble height in spring-summer 2011. Plants were harvested at consecutive leaf-appearance intervals to measure nutritive value up to the four-leaf stage. In parallel, leaf morphogenetic traits (appearance, elongation and lifespan) and sheath length of the successive leaves produced on marked tillers were measured. LeafNDFcontents remained stable with increasing leaf age and length but showed a marked variation across seasons. Leaf NDFD and DMD showed a consistent decrease with increasing leaf age and length, and irrespective of growing season or residual pasture height. The negative effect of leaf age and length on digestibility was related to variations in sheath tube length and associated differences in leaf appearance and elongation rates. These findings highlight the relevance of monitoring the sheath tube length as a complementary measure to leaf stage for further management of the NDFD and DMD of grass forages. Although the focus of this study was tall fescue swards, the same morphogenetic implications on forage nutritive value could apply to other temperate and tropical grass species; however, the testing of this hypothesis warrants carefully controlled investigations. [ABSTRACT FROM AUTHOR]

Background and Aims Protosphagnalean mosses constitute the largest group of extinct mosses of still uncertain affinity. Having the general morphology of the Bryopsida, some have leaves with an areolation pattern characteristic of modern Sphagna. This study describes the structure and variation of these patterns in protosphagnalean mosses and provides a comparison with those of modern Sphagna. Methods Preparations of fossil mosses showing preserved leaf cell structure were obtained by dissolving rock, photographed, and the resulting images were transformed to graphical format and analysed with Areoana computer software. Key Results The sphagnoid areolation pattern is identical in its basic structure for both modern Sphagnum and Palaeozoic protosphagnalean mosses. However, in the former group the pattern develops through unequal oblique cell divisions, while in the latter the same pattern is a result of equal cell divisions taking place in a specific order with subsequent uneven cell growth. The protosphagnalean pathway leads to considerable variability in leaf structure. Conclusions Protosphagnalean mosses had a unique ability to switch the development of leaf areolation between a pathway unique to Sphagnum and another one common to all other mosses. This developmental polyvariancy hinders attempts to classify these mosses, as characters previously considered to be of generic significance can be shown to co-occur in one individual leaf. New understanding of the ontogeny has allowed us to re-evaluate the systematic significance of such diagnostic characters in these Palaeozoic plants, showing that their similarity to Sphagnum is less substantial. [ABSTRACT FROM AUTHOR]

Abstract: Leaves are the most conspicuous planar organs in plants, designed for efficient capture of sunlight and its conversion to energy that is channeled into sustaining the entire biosphere. How a few founder cells derived from the shoot apical meristem give rise to diverse leaf forms has interested naturalists and developmental biologists alike. At the heart of leaf morphogenesis lie two simple cellular processes, division and expansion, that are spatially and temporally segregated in a developing leaf. In leaves of dicot model species, cell division occurs predominantly at the base, concomitant with the expansion and differentiation of cells at the tip of the lamina that drives increase in leaf surface area. The timing of the transition from one cell fate (division) to the other (expansion) within a growing leaf lamina is a critical determinant of final leaf shape, size, complexity and flatness. The TCP proteins, unique to plant kingdom, are sequence‐specific DNA‐binding transcription factors that control several developmental and physiological traits. A sub‐group of class II TCPs, called CINCINNATA‐like TCPs (CIN‐TCPs henceforth), are key regulators of the timing of the transition from division to expansion in dicot leaves. The current review highlights recent advances in our understanding of how the pattern of CIN‐TCP activity is translated to the dynamic spatio‐temporal control of cell‐fate transition through the transactivation of cell‐cycle regulators, growth‐repressing microRNAs, and interactions with the chromatin remodeling machinery to modulate phytohormone responses. Unravelling how environmental inputs influence CIN‐TCP‐mediated growth control is a challenge for future studies. © 2018 IUBMB Life, 70(8):718–731, 2018 [ABSTRACT FROM AUTHOR]

Under different red (R):blue (B) photon flux ratios, the growth performance of rapeseed (Brassica napus L.) is significantly different. Rapeseed under high R ratios shows shade response, while under high B ratios it shows sun-type morphology. Rapeseed under monochromatic red or blue light is seriously stressed. Transcriptomic and proteomic methods were used to analyze the metabolic pathway change of rapeseed (cv. “Zhongshuang 11”) leaves under different R:B photon flux ratios (including 100R:0B%, 75R:25B%, 25R:75B%, and 0R:100B%), based on digital gene expression (DGE) and two-dimensional gel electrophoresis (2-DE). For DGE analysis, 2054 differentially expressed transcripts (|log2(fold change)|≥1, q<0.005) were detected among the treatments. High R ratios (100R:0B% and 75R:25B%) enhanced the expression of cellular structural components, mainly the cell wall and cell membrane. These components participated in plant epidermis development and anatomical structure morphogenesis. This might be related to the shade response induced by red light. High B ratios (25R:75B% and 0R:100B%) promoted the expression of chloroplast-related components, which might be involved in the formation of sun-type chloroplast induced by blue light. For 2-DE analysis, 37 protein spots showed more than a 2-fold difference in expression among the treatments. Monochromatic light (ML; 100R:0B% and 0R:100B%) stimulated accumulation of proteins associated with antioxidation, photosystem II (PSII), DNA and ribosome repairs, while compound light (CL; 75R:25B% and 25R:75B%) accelerated accumulation of proteins associated with carbohydrate, nucleic acid, amino acid, vitamin, and xanthophyll metabolisms. These findings can be useful in understanding the response mechanisms of rapeseed leaves to different R:B photon flux ratios. [ABSTRACT FROM AUTHOR]

Leaves are the major plant organs with a primary function for photosynthesis. Auxin controls various aspects of plant growth and development, including leaf initiation, expansion and differentiation. Unique and intriguing auxin features include its polar transport, which is mainly controlled by the AUX1/LAX and PIN gene families as influx and efflux carriers, respectively. The role of AUX1/LAX genes in root development is well documented, but the role of these genes in leaf morphogenesis remains unclear. Moreover, most studies have been conducted in the plant model Arabidopsis thaliana, while studies in tomato are still scarce. In this study, we isolated six lines of the allelic curly leaf phenotype 'curl' mutants from a γ-ray and EMS (ethyl methanesulfonate) mutagenized population. Using a map-based cloning strategy combined with exome sequencing, we observed that a mutation occurred in the SlLAX1 gene (Solyc09g014380), which is homologous to an Arabidopsis auxin influx carrier gene, AUX1 (AtAUX1). Characterization of six alleles of single curl mutants revealed the pivotal role of SlLAX1 in controlling tomato leaf flatness by balancing adaxial and abaxial pavement cell growth, which has not been reported in tomato. Using TILLING (Targeting Induced Local Lesions IN Genome) technology, we isolated an additional mutant allele of the SlLAX1 gene and this mutant showed a curled leaf phenotype similar to other curl mutants, suggesting that Solyc09g014380 is responsible for the curl phenotype. These results showed that SlLAX1 is required for normal leaf development mediated by balanced adaxial and abaxial pavement cell growth in tomato. [ABSTRACT FROM AUTHOR]

The ANGUSTIFOLIA (AN) gene in Arabidopsis is important for a plethora of morphological phenotypes. Recently, AN was also reported to be involved in responses to biotic and abiotic stresses. It encodes a homolog of the animal C-terminal binding proteins (CtBPs). In contrast to animal CtBPs, AN does not appear to function as a transcriptional co-repressor and instead functions outside nucleus where it might be involved in Golgi-associated membrane trafficking. In this study, we report a novel and unexplored role of AN as a component of stress granules (SGs). Interaction studies identified several RNA binding proteins that are associated with AN. AN co-localizes with several messenger ribonucleoprotein granule markers to SGs in a stress dependent manner. an mutants exhibit an altered SG formation. We provide evidence that the NAD(H) binding domain of AN is relevant in this context as proteins carrying mutations in this domain localize to a much higher degree to SGs and strongly reduce AN dimerization and its interaction with one interactor but not the others. Finally, we show that AN is a negative regulator of salt and osmotic stress responses in Arabidopsis suggesting a functional relevance in SGs.

Inspired by the differential-growth-driven morphogenesis of leaves, flowers, and other tissues, there is increasing interest in artificial analogs of these shape-shifting thin sheets made of active materials that respond to environmental stimuli such as heat, light, and humidity. But how can we determine the growth patterns to achieve a given shape from another shape? We solve this geometric inverse problem of determining the growth factors and directions (the metric tensors) for a given isotropic elastic bilayer to grow into a target shape by posing and solving an elastic energy minimization problem. A mathematical equivalence between bilayers and curved monolayers simplifies the inverse problem considerably by providing algebraic expressions for the growth metric tensors in terms of those of the final shape. This approach also allows us to prove that we can grow any target surface from any reference surface using orthotropically growing bilayers. We demonstrate this by numerically simulating the growth of a flat sheet into a face, a cylindrical sheet into a flower, and a flat sheet into a complex canyon-like structure. [ABSTRACT FROM AUTHOR]

In order to explore the functional conservation of JAGGED, a key gene involved in the sculpting of lateral organs in several model species, we identified its ortholog Aq JAG in the lower eudicot species Aquilegia coerulea., We analyzed the expression patterns of Aq JAG in various tissues and developmental stages, and used RNAi-based methods to generate knockdown phenotypes of Aq JAG., Aq JAG was strongly expressed in shoot apices, floral meristems, lateral root primordia and all lateral organ primordia. Silencing of Aq JAG revealed a wide range of defects in the developing stems, leaves and flowers; strongest phenotypes include severe reduction of leaflet laminae due to a decrease in cell size and number, change of adaxial cell identity, outgrowth of laminar-like tissue on the inflorescence stem, and early arrest of floral meristems and floral organ primordia., Our results indicate that Aq JAG plays a critical role in controlling primordia initiation and distal growth of floral organs, and laminar development of leaflets. Most strikingly, we demonstrated that Aq JAG disproportionally controls the behavior of cells with adaxial identity in vegetative tissues, providing evidence of how cell proliferation is controlled in an identity-specific manner. [ABSTRACT FROM AUTHOR]

In plants the dorsoventral boundary of leaves defines an axis of symmetry through the centre of the organ separating the top (dorsal) and bottom (ventral) tissues. Although the positioning of this boundary is critical for leaf morphogenesis, how the boundary is established and how it influences development remains unclear. Using live-imaging and perturbation experiments we show that leaf orientation, morphology and position are pre-patterned by HD-ZIPIII and KAN gene expression in the shoot, leading to a model in which dorsoventral genes coordinate to regulate plant development by localizing auxin response between their expression domains. However we also find that auxin levels feedback on dorsoventral patterning by spatially organizing HD-ZIPIII and KAN expression in the shoot periphery. By demonstrating that the regulation of these genes by auxin also governs their response to wounds, our results also provide a parsimonious explanation for the influence of wounds on leaf dorsoventrality. [ABSTRACT FROM AUTHOR]

Background: TIR1-like proteins act as auxin receptors and play essential roles in auxin-mediated plant development processes. The number of auxin receptor family members varies among species. While the functions of auxin receptor genes have been widely studied in Arabidopsis, the distinct functions of cucumber (Cucumis sativus L.) auxin receptors remains poorly understood. To further our understanding of their potential role in cucumber development, two TIR1- like genes were identified and designated CsTIR1 and CsAFB2. In the present study, tomato (Sonanum lycopersicum) was used as a model to investigate the phenotypic and molecular changes associated with the overexpression of CsTIR1 and CsAFB2. Results: Differences in the subcellular localizations of CsTIR1 and CsAFB2 were identified and both genes were actively expressed in leaf, female flower and young fruit tissues of cucumber. Moreover, CsTIR1- and CsAFB2-overexpressing lines exhibited pleotropic phenotypes ranging from leaf abnormalities to seed germination and parthenocarpic fruit compared with the wild-type plants. To further elucidate the regulation of CsTIR1 and CsAFB2, the role of the miR393/ TIR1 module in regulating cucumber fruit set were investigated. Activation of miR393-mediated mRNA cleavage of CsTIR1 and CsAFB2 was revealed by qPCR and semi-qPCR, which highlighted the critical role of the miR393/TIR1 module in mediating fruit set development in cucumber. Conclusion: Our results provide new insights into the involvement of CsTIR1 and CsAFB2 in regulating various phenotype alterations, and suggest that post-transcriptional regulation of CsTIR1 and CsAFB2 mediated by miR393 is essential for cucumber fruit set initiation. Collectively, these results further clarify the roles of cucumber TIR1 homologs and miR393 in regulating fruit/seed set development and leaf morphogenesis. [ABSTRACT FROM AUTHOR]