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Background: Inflorescence architecture and floral development in flowering plants are determined by genetic control of meristem identity, determinacy, and maintenance. The ear inflorescence meristem in maize (Zea mays) initiates short branch meristems called spikelet pair meristems, thus unlike the tassel inflorescence, the ears lack long branches. Maize growth-regulating factor (GRF)-interacting factor1 (GIF1) regulates branching and size of meristems in the tassel inflorescence by binding to Unbranched3. However, the regulatory pathway of gif1 in ear meristems is relatively unknown., Result: In this study, we found that loss-of-function gif1 mutants had highly branched ears, and these extra branches repeatedly produce more branches and florets with unfused carpels and an indeterminate floral apex. In addition, GIF1 interacted in vivo with nine GRFs, subunits of the SWI/SNF chromatin-remodeling complex, and hormone biosynthesis-related proteins. Furthermore, key meristem-determinacy gene RAMOSA2 (RA2) and CLAVATA signaling-related gene CLV3/ENDOSPERM SURROUNDING REGION (ESR) 4a (CLE4a) were directly bound and regulated by GIF1 in the ear inflorescence., Conclusions: Our findings suggest that GIF1 working together with GRFs recruits SWI/SNF chromatin-remodeling ATPases to influence DNA accessibility in the regions that contain genes involved in hormone biosynthesis, meristem identity and determinacy, thus driving the fate of axillary meristems and floral organ primordia in the ear-inflorescence of maize., (© 2022. The Author(s).)

Shoot branching is a complex mechanism in which secondary shoots grow from buds that are initiated from meristems established in leaf axils. The model plant Arabidopsis (Arabidopsis thaliana) has a rosette leaf growth pattern in the vegetative stage. After flowering initiation, the main stem elongates with the top leaf primordia developing into cauline leaves. Meristems in Arabidopsis initiate in the axils of rosette or cauline leaves, giving rise to rosette or cauline buds, respectively. Plasticity in the process of shoot branching is regulated by resource and nutrient availability as well as by plant hormones. However, few studies have attempted to test whether cauline and rosette branching are subject to the same plasticity. Here, we addressed this question by phenotyping cauline and rosette branching in three Arabidopsis ecotypes and several Arabidopsis mutants with varied shoot architectures. Our results showed no negative correlation between cauline and rosette branch numbers in Arabidopsis, demonstrating that there is no tradeoff between cauline and rosette bud outgrowth. Through investigation of the altered branching pattern of flowering pathway mutants and Arabidopsis ecotypes grown in various photoperiods and light regimes, we further elucidated that the number of cauline branches is closely related to flowering time. The number of rosette branches has an enormous plasticity compared with cauline branches and is influenced by genetic background, flowering time, light intensity, and temperature. Our data reveal different levels of plasticity in the regulation of branching at rosette and cauline nodes, and promote a framework for future branching analyses., (© American Society of Plant Biologists 2021. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Flowers are produced by floral meristems, groups of stem cells that give rise to floral organs. In grasses, including the major cereal crops, flowers (florets) are contained in spikelets, which contain one to many florets, depending on the species. Importantly, not all grass florets are developmentally equivalent, and one or more florets are often sterile or abort in each spikelet. Members of the Andropogoneae tribe, including maize (Zea mays), produce spikelets with two florets; the upper and lower florets are usually dimorphic, and the lower floret is greatly reduced compared to the upper floret. In maize ears, early development appears identical in both florets but the lower floret ultimately aborts. To gain insight into the functional differences between florets with different fates, we used laser capture microdissection coupled with RNA-sequencing to globally examine gene expression in upper and lower floral meristems in maize. Differentially expressed genes were involved in hormone regulation, cell wall, sugar, and energy homeostasis. Furthermore, cell wall modifications and sugar accumulation differed between the upper and lower florets. Finally, we identified a boundary domain between upper and lower florets, which we hypothesize is important for floral meristem activity. We propose a model in which growth is suppressed in the lower floret by limiting sugar availability and upregulating genes involved in growth repression. This growth repression module may also regulate floret fertility in other grasses and potentially be modulated to engineer more productive cereal crops., (© American Society of Plant Biologists 2021. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Plant architecture is defined by fates and positions of meristematic tissues and has direct consequences on yield potential and environmental adaptation of the plant. In strawberries (Fragaria vesca L. and F. × ananassa Duch.), shoot apical meristems can remain vegetative or differentiate into a terminal inflorescence meristem. Strawberry axillary buds (AXBs) are located in leaf axils and can either remain dormant or follow one of the two possible developmental fates. AXBs can either develop into stolons needed for clonal reproduction or into branch crowns (BCs) that can bear their own terminal inflorescences under favorable conditions. Although AXB fate has direct consequences on yield potential and vegetative propagation of strawberries, the regulation of AXB fate has so far remained obscure. We subjected a number of woodland strawberry (F. vesca L.) natural accessions and transgenic genotypes to different environmental conditions and growth regulator treatments to demonstrate that strawberry AXB fate is regulated either by environmental or endogenous factors, depending on the AXB position on the plant. We confirm that the F. vesca GIBBERELLIN20-oxidase4 (FvGA20ox4) gene is indispensable for stolon development and under tight environmental regulation. Moreover, our data show that apical dominance inhibits the outgrowth of the youngest AXB as BCs, although the effect of apical dominance can be overrun by the activity of FvGA20ox4. Finally, we demonstrate that the FvGA20ox4 is photoperiodically regulated via FvSOC1 (F. vesca SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1) at 18°C, but at higher temperature of 22°C an unidentified FvSOC1-independent pathway promotes stolon development., (© The Author(s) 2021. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Plants generate a large variety of shoot forms with regular geometries. These forms emerge primarily from the activity of a stem cell niche at the shoot tip. Recent efforts have established a theoretical framework of form emergence at the shoot tip, which has empowered the use of modelling in conjunction with biological approaches to begin to disentangle the biochemical and physical mechanisms controlling form development at the shoot tip. Here, we discuss how these advances get us closer to identifying the construction principles of plant shoot tips. Considering the current limits of our knowledge, we propose a roadmap for developing a general theory of form development at the shoot tip.

Polyamines (PAs) dramatically affect root architecture and development, mainly by unknown mechanisms; however, accumulating evidence points to hormone signaling and reactive oxygen species (ROS) as candidate mechanisms. To test this hypothesis, PA levels were modified by progressively reducing ADC1/2 activity and Put levels, and then changes in root meristematic zone (MZ) size, ROS, and auxin and cytokinin (CK) signaling were investigated. Decreasing putrescine resulted in an interesting inverted-U-trend in primary root growth and a similar trend in MZ size, and differential changes in putrescine (Put), spermidine (Spd), and combined spermine (Spm) plus thermospermine (Tspm) levels. At low Put concentrations, ROS accumulation increased coincidently with decreasing MZ size, and treatment with ROS scavenger KI partially rescued this phenotype. Analysis of double AtrbohD/F loss-of-function mutants indicated that NADPH oxidases were not involved in H 2 O 2 accumulation and that elevated ROS levels were due to changes in PA back-conversion, terminal catabolism, PA ROS scavenging, or another pathway. Decreasing Put resulted in a non-linear trend in auxin signaling, whereas CK signaling decreased, re-balancing auxin and CK signaling. Different levels of Put modulated the expression of PIN1 and PIN2 auxin transporters, indicating changes to auxin distribution. These data strongly suggest that PAs modulate MZ size through both hormone signaling and ROS accumulation in Arabidopsis .

Root system architecture (RSA) is a key factor in the efficiency of nutrient capture and water uptake in plants. Understanding the genetic control of RSA will be useful in minimizing fertilizer and water usage in agricultural cropping systems. Using a hydroponic screen and a gel-based imaging system, we identified a rice (Oryza sativa) gene, VAP-RELATED SUPPRESSOR OF TOO MANY MOUTHS1 (OsVST1), which plays a key role in controlling RSA. This gene encodes a homolog of the VAP-RELATED SUPPRESSORS OF TOO MANY MOUTHS (VST) proteins in Arabidopsis (Arabidopsis thaliana), which promote signaling in stomata by mediating plasma membrane-endoplasmic reticulum contacts. OsVST1 mutants have shorter primary roots, decreased root meristem size, and a more compact RSA. We show that the Arabidopsis VST triple mutants have similar phenotypes, with reduced primary root growth and smaller root meristems. Expression of OsVST1 largely complements the short root length and reduced plant height in the Arabidopsis triple mutant, supporting conservation of function between rice and Arabidopsis VST proteins. In a field trial, mutations in OsVST1 did not adversely affect grain yield, suggesting that modulation of this gene could be used as a way to optimize RSA without an inherent yield penalty., (© American Society of Plant Biologists 2020. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Organ morphologies are diverse but also conserved under shared developmental constraints among species. Any geometrical similarities in the shape behind diversity and the underlying developmental constraints remain unclear. Plant root tip outlines commonly exhibit a dome shape, which likely performs physiological functions, despite the diversity in size and cellular organization among distinct root classes and/or species. We carried out morphometric analysis of the primary roots of ten angiosperm species and of the lateral roots (LRs) of Arabidopsis , and found that each root outline was isometrically scaled onto a parameter-free catenary curve, a stable structure adopted for arch bridges. Using the physical model for bridges, we analogized that localized and spatially uniform occurrence of oriented cell division and expansion force the LR primordia (LRP) tip to form a catenary curve. These growth rules for the catenary curve were verified by tissue growth simulation of developing LRP development based on time-lapse imaging. Consistently, LRP outlines of mutants compromised in these rules were found to deviate from catenary curves. Our analyses demonstrate that physics-inspired growth rules constrain plant root tips to form isometrically scalable catenary curves., Competing Interests: Competing interestsThe authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2021. Published by The Company of Biologists Ltd.)

The modification of shoot architecture and increased investment into reproductive structures is key for crop improvement and is achieved through coordinated changes in the development and determinacy of different shoot meristems. A fundamental question is how the development of different shoot meristems is genetically coordinated to optimize the balance between vegetative and reproductive organs. Here we identify the MANY NODED DWARF1 ( HvMND1 ) gene as a major regulator of plant architecture in barley ( Hordeum vulgare ). The mnd1.a mutant displayed an extended vegetative program with increased phytomer, leaf, and tiller production but a reduction in the number and size of grains. The induction of vegetative structures continued even after the transition to reproductive growth, resulting in a marked increase in longevity. Using mapping by RNA sequencing, we found that the HvMND1 gene encodes an acyl-CoA N -acyltransferase that is predominately expressed in developing axillary meristems and young inflorescences. Exploration of the expression network modulated by HvMND1 revealed differential expression of the developmental microRNAs miR156 and miR172 and several key cell cycle and developmental genes. Our data suggest that HvMND1 plays a significant role in the coordinated regulation of reproductive phase transitions, thereby promoting reproductive growth and whole plant senescence in barley., (© 2020 American Society of Plant Biologists. All Rights Reserved.)

As the sister group to seed plants, ferns are a phylogenetically informative lineage. Functional studies in representatives of the fern lineage are helping bridge the knowledge gap in developmental mechanisms between angiosperms and non-vascular plants. The fern life cycle has the advantage of combining a sizable free-living haploid gametophyte, more amenable for developmental studies than the reduced seed plant gametophyte, with an indeterminate and complex diploid sporophyte. Ceratopteris richardii has long been proposed as a model fern and has recently become tractable due to stable transgenesis and increasing genomic resources, allowing researchers to test explicit questions about gene function in a fern for the first time. As with any model system, a detailed understanding of wild-type morphology and a staged ontogeny are indispensable for the characterization of mutant phenotypes resulting from genetic manipulations. Therefore, the goal of this study is to provide a unified reference ontogeny for this emerging model fern as a tool for comparative evolutionary and developmental studies. It complements earlier research by filling gaps in major stages of development of the haploid gametophyte and diploid sporophyte generations, and provides additional descriptions of the shoot apical meristem and early leaf development. This resource is meant to facilitate not only studies of candidate genes within C. richardii, but also broader ontogenetic comparisons to other model plants., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Main Conclusion: Morphological and genetic markers indicate that in sorghum, the juvenile-to-adult phase transition occurs during the fourth and fifth leaf stages. This timing differs from those reported for other plants. The juvenile-to-adult (JA) phase transition is an important event for optimizing vegetative growth and reproductive success in plants. Among the Poaceae crops, which are a vital food source for humans, studies of the JA phase transition have been restricted to rice and maize. We studied the morphological and genetic changes that occur during the early development of sorghum and found that dramatic changes occur in shoot architecture during the early vegetative stages. Changes were observed in leaf size, leaf shape, numbers of trichomes, and size of the shoot apical meristem. In particular, the length/width ratios of the leaf blades in the fifth and upper leaves were completely different from those of the second to fourth leaves. The fifth and upper leaves have trichomes on their adaxial sides, which were absent on the lower leaves. We also analyzed expression of two microRNAs that are known to be molecular markers of the JA phase transition and found that expression of miR156 was highest in the second to fourth leaves and then was gradually down-regulated, whereas miR172 expression followed the opposite pattern. These results suggest that in sorghum, the second and third leaves represent the juvenile phase, the fourth and fifth leaves are in the transition stage, and the sixth and upper leaves are in the adult phase. Thus, the JA phase transition occurs during the fourth and fifth leaf stages. These findings are expected to be useful for understanding the early development of sorghum.

Reproductive success in plants is dependent on many factors but the precise timing of flowering is certainly among the most crucial. Perennial plants often have a vernalization or over-wintering requirement in order to successfully flower in the spring. The shoot apical meristem undergoes drastic developmental and molecular changes as it transitions into inflorescence meristem (IM) identity, which then gives rise to floral meristems (FMs). In this study, we have examined the developmental and gene expression changes underlying the transition from the vegetative to reproductive phases in the basal eudicot Aquilegia coerulea , which has evolved a vernalization response independently relative to other established model systems. Results from both our histology and scanning electron studies demonstrate that developmental changes in the meristem occur gradually during the third and fourth weeks of vernalization. Based on RNAseq data and cluster analysis, several known flowering time loci, including AqFT and AqFL1 , exhibit dramatic changes in expression during the fourth week. Further consideration of candidate gene homologs as well as unexpected loci of interest creates a framework in which we can begin to explore the genetic basis of the flowering time transition in Aquilegia .

The introgression of a small segment of wheat (Triticum aestivum L.) chromosome arm 1BS in the distal region of the rye (Secale cereale L.) 1RS.1BL arm translocation in wheat (henceforth 1RSRW) was previously associated with reduced grain yield, carbon isotope discrimination, and stomatal conductance, suggesting reduced access to soil moisture. Here we show that lines with the normal 1RS arm have longer roots than lines with the 1RSRW arm in both field and hydroponic experiments. In the 1RSRW lines, differences in seminal root length were associated with a developmentally regulated arrest of the root apical meristem (RAM). Approximately 10 d after germination, the seminal roots of the 1RSRW plants showed a gradual reduction in elongation rate, and stopped growing a week later. Seventeen days after germination, the roots of the 1RSRW plants showed altered gradients of reactive oxygen species and emergence of lateral roots close to the RAM, suggesting changes in the root meristem. The 1RSRW lines also showed reduced biomass (estimated by the normalized difference vegetation index) and grain yield relative to the 1RS lines, with larger differences under reduced or excessive irrigation than under normal irrigation. These results suggest that this genetic variation could be useful to modulate root architecture., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Kernel row number is a fundamental component of maize (Zea mays) yield and an important target for maize breeding. The revolutionary transition from the two-rowed teosinte to maize with increased kernel row numbers dramatically enhanced yields during domestication. Kernel row number is controlled by many quantitative trait loci (QTLs), however most genes responsible for these QTLs remain uncharacterised and the molecular genetic mechanisms are unknown. Here, we combined map-based cloning and association mapping to identify a major QTL for kernel row number, krn1, which is likely to correspond to an existing gene (ids1/Ts6) encoding an AP2 domain protein homologous to the product of the wheat key domestication gene Q. The increased expression of ids1/Ts6 in two maize mutants increased spikelet pair meristem numbers and then enhanced kernel row numbers. Nucleotide diversity analysis further revealed that ids1/Ts6 and Q were under strong parallel selection in maize and wheat that increased their yields during domestication or improvement. RNA-seq revealed that ids1/Ts6 is involved in multiple pathways regulating spikelet pair meristem development, involving several key genes such as fea3, fea4 and ra3. The cloning of the krn1 gene will pave a new way to efficiently improve maize yield in the near future., (© 2019 The Authors. New Phytologist © 2019 New Phytologist Trust.)

During the transition to the reproductive phase, the shoot apical meristem switches from the developmental program that generates vegetative organs to instead produce flowers. In this study, we examined the genetic interactions of FLOWERING LOCUS T (FT)/TWIN SISTER OF FT (TSF) and TERMINAL FLOWER 1 (TFL1) in the determination of inflorescence meristem identity in Arabidopsis thaliana. The ft-10 tsf-1 mutants produced a compact inflorescence surrounded by serrated leaves (hyper-vegetative shoot) at the early bolting stage, as did plants overexpressing TFL1. Plants overexpressing FT or TSF (or both FT and TFL1) generated a terminal flower, as did tfl1-20 mutants. The terminal flower formed in tfl1-20 mutants converted to a hyper-vegetative shoot in ft-10 tsf-1 mutants. Grafting ft-10 tsf-1 or ft-10 tsf-1 tfl1-20 mutant scions to 35S::FT rootstock plants produced a normal inflorescence and a terminal flower in the scion plants, respectively, although both scions showed similar early flowering. Misexpression of FT in the vasculature and in the shoot apex in wild-type plants generated a normal inflorescence and a terminal flower, respectively. By contrast, in ft-10 tsf-1 mutants the vasculature-specific misexpression of FT converted the hyper-vegetative shoot to a normal inflorescence, and in the ft-10 tsf-1 tfl1-20 mutants converted the shoot to a terminal flower. TFL1 levels did not affect the inflorescence morphology caused by FT/TSF overexpression at the early bolting stage. Taking these results together, we proposed that FT/TSF and TFL1 play antagonistic roles in the determination of inflorescence meristem identity, and that FT/TSF are more important than TFL1 in this process., (© 2019 The Authors The Plant Journal © 2019 John Wiley & Sons Ltd.)

In early seedlings, the primary root adapts rapidly to environmental changes through the modulation of endogenous hormone levels. The phytohormone ethylene inhibits primary root elongation, but the underlying molecular mechanism of how ethylene-reduced root growth is modulated in environmental changes remains poorly understood. Here, we show that a novel rice (Oryza sativa) DOF transcription factor OsDOF15 positively regulates primary root elongation by regulating cell proliferation in the root meristem, via restricting ethylene biosynthesis. Loss-of-function of OsDOF15 impaired primary root elongation and cell proliferation in the root meristem, whereas OsDOF15 overexpression enhanced these processes, indicating that OsDOF15 is a key regulator of primary root elongation. This regulation involves the direct interaction of OsDOF15 with the promoter of OsACS1, resulting in the repression of ethylene biosynthesis. The control of ethylene biosynthesis by OsDOF15 in turn regulates cell proliferation in the root meristem. OsDOF15 transcription is repressed by salt stress, and OsDOF15-mediated ethylene biosynthesis plays a role in inhibition of primary root elongation by salt stress. Thus, our data reveal how the ethylene-inhibited primary root elongation is finely controlled by OsDOF15 in response to environmental signal, a novel mechanism of plants responding to salt stress and transmitting the information to ethylene biosynthesis to restrict root elongation., (© 2019 The Authors. New Phytologist © 2019 New Phytologist Trust.)

Plant height (PH) and plant width (PW), two of the major plant architectural traits determining the yield and productivity of a crop, are defined by diverse morphometric characteristics of the shoot apical meristem (SAM). The identification of potential molecular tags from a single gene that simultaneously modulates these plant/SAM architectural traits is therefore prerequisite to achieve enhanced yield and productivity in crop plants, including chickpea. Large-scale multienvironment phenotyping of the association panel and mapping population have ascertained the efficacy of three vital SAM morphometric trait parameters, SAM width, SAM height and SAM area, as key indicators to unravel the genetic basis of the wide PW and PH trait variations observed in desi chickpea. This study integrated a genome-wide association study (GWAS); quantitative trait locus (QTL)/fine-mapping and map-based cloning with molecular haplotyping; transcript profiling; and protein-DNA interaction assays for the dissection of plant architectural traits in chickpea. These exertions delineated natural alleles and superior haplotypes from a CabHLH121 transcription factor (TF) gene within the major QTL governing PW, PH and SAM morphometric traits. A genome-wide protein-DNA interaction assay assured the direct binding of a known stem cell master regulator, CaWUS, to the WOX-homeodomain TF binding sites of a CabHLH121 gene and its constituted haplotypes. The differential expression of CaWUS and transcriptional regulation of its target CabHLH121 gene/haplotypes were apparent, suggesting their collective role in altering SAM morphometric characteristics and plant architectural traits in the contrasting near isogenic lines (NILs). The NILs introgressed with a superior haplotype of a CabHLH121 exhibited optimal PW and desirable PH as well as enhanced yield and productivity without compromising any component of agronomic performance. These molecular signatures of the CabHLH121 TF gene have the potential to regulate both PW and PH traits through the modulation of proliferation, differentiation and maintenance of the meristematic stem cell population in the SAM; therefore, these signatures will be useful in the translational genomic study of chickpea genetic enhancement. The restructured cultivars with desirable PH (semidwarf) and PW will ensure maximal planting density in a specified cultivable field area, thereby enhancing the overall yield and productivity of chickpea. This can essentially facilitate the achievement of better remunerative outputs by farmers with rational land use, therefore ensuring global food security in the present scenario of an increasing population density and shrinking per capita land area., (© 2019 The Authors The Plant Journal © 2019 John Wiley & Sons Ltd.)

The root system displays a remarkable plasticity that enables plants to adapt to changing environmental conditions. This plasticity is tightly linked to the activity of root apical meristems (RAMs) and to the formation of lateral roots, both controlled by related hormonal crosstalks. In Arabidopsis thaliana, gibberellins (GAs) were shown to positively control RAM growth and the formation of lateral roots. However, we showed in Medicago truncatula that GAs negatively regulate root growth and RAM size as well as the number of lateral roots depending at least on the MtDELLA1 protein. By using confocal microscopy and molecular analyses, we showed that GAs primarily regulate RAM size by affecting cortical cell expansion and additionally negatively regulate a subset of cytokinin-induced root expansin encoding genes. Moreover, GAs reduce the number of cortical cell layers, resulting in the formation of both shorter and thinner roots. These results suggest contrasting effects of GA regulations on the root system architecture depending on plant species.

Context: Yield improvement is an important issue for rice breeding. Panicle architecture is one of the key components of rice yield and exhibits a large diversity. To identify the morphological and genetic determinants of panicle architecture, we performed a detailed phenotypic analysis and a genome-wide association study (GWAS) using an original panel of Vietnamese landraces., Results: Using a newly developed image analysis tool, morphological traits of the panicles were scored over two years: rachis length; primary, secondary and tertiary branch number; average length of primary and secondary branches; average length of internode on rachis and primary branch. We observed a high contribution of spikelet number and secondary branch number per panicle to the overall phenotypic diversity in the dataset. Twenty-nine stable QTLs associated with seven traits were detected through GWAS over the two years. Some of these QTLs were associated with genes already implicated in panicle development. Importantly, the present study revealed the existence of new QTLs associated with the spikelet number, secondary branch number and primary branch number traits., Conclusions: Our phenotypic analysis of panicle architecture variation suggests that with the panel of samples used, morphological diversity depends largely on the balance between indeterminate vs. determinate axillary meristem fate on primary branches, supporting the notion of differences in axillary meristem fate between rachis and primary branches. Our genome-wide association study led to the identification of numerous genomic sites covering all the traits studied and will be of interest for breeding programs aimed at improving yield. The new QTLs detected in this study provide a basis for the identification of new genes controlling panicle development and yield in rice.

The Daodi herb, Huangqi from Shanxi, is derived from the root of Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao. Huangqi was divided into different commercial specifications and grades in producing area according to macroscopic features. Developmental anatomy of anomalous structure of the perennial fresh main root of A. membranaceus var. mongholicus was investigated using conventional paraffin section to explore the relationship between anomalous structure and classification of commercial specifications and grades of Huangqi. The results of developmental anatomy showed that parenchyma cells in secondary phloem and secondary xylem of the perennial fresh main root regained meristematic ability, and resulted in anomalous structure. Several layers of additional periderm could sometimes be found in the secondary phloem near the initial periderm, which was called rhytidome. Additional periderm could sometimes be observed in the center of secondary xylem, which was described as "rotten heart." The area of rhytidome and "rotten heart" increased gradually with increasing age. The results of different commercial specifications and grades of Huangqi revealed rhytidome and "rotten heart" mainly existed in Ge-Da-Tou, Er-Dao-Tou, Hong-Lan-Qi, Special Class, First Class, and Second Class. The additional periderm in secondary phloem of Ge-Da-Tou, Er-Dao-Tou, Hong-Lan-Qi, and Special Class could reach five layers; however, that of First Class and Second Class was three layers at most. In summary, this study demonstrated the rules of the development of rhytidome and "rotten heart" in A. membranaceus var. mongholicus. The relationship between anomalous structure and different commercial specifications and grades of Daodi herb Huangqi, was clarified. RESEARCH HIGHLIGHTS: The rhytidome and the development of "rotten heart" have not been reported in Astragalus membranaceus var. mongholicus. At present article, we demonstrated the developmental anatomy of the rhytidome and "rotten heart" existed in the secondary phloem and secondary xylem of the root of A. membranaceus var. mongholicus respectively. The rhytidome and "rotten heart" is different among six commercial specifications and grades of Huangqi., (© 2018 Wiley Periodicals, Inc.)

Premise of the Study: The apical meristem generates indeterminate apical growth of the stem and root of vascular plants. Our previous examination showed that shoot apical meristems (SAMs) can be classified into two types based on plasmodesmatal networks (PNs), which are important elements in symplasmic signaling pathways within the apical meristem. Here, we examined the PNs of root apical meristems (RAMs) in comparison with those of SAMs., Methods: Root apical meristems of 18 families and 22 species of lycophytes and euphyllophytes were analyzed. Plasmodesmata (PD) in cell walls in median longitudinal sections of RAMs were enumerated using transmission electron micrographs, and the PD density per 1 μm 2 of each cell wall was calculated., Key Results: Root apical meristems with prominent apical cells of monilophytes (euphyllophytes) and Selaginellaceae (lycophytes) had high PD densities, while RAMs with plural initial cells of gymnosperms and angiosperms (euphyllophytes), and of Lycopodiaceae and Isoetaceae (lycophytes) had low PD densities. This correlation between structures of apical meristems and PD densities is identical to that in SAMs already described., Conclusions: Irrespective of their diversified structures, the RAMs of vascular plants can be classified into two types with respect to PNs: the fern (monilophyte) type, which has a lineage-specific PN with only primary PD, and the seed-plant type, which has an interspecific PN with secondary PD in addition to primary PD. PNs may have played a key role in the evolution of apical meristems in vascular plants., (© 2018 Botanical Society of America.)

The suppression of apical growth and radial trunk growth in trees under shade is a key factor in the competition mechanism among individuals in natural and artificial forests. However, the timing of apical and radial growth suppression after shading and the physiological processes involved have not been evaluated precisely. Twenty-one Abies sachalinensis seedlings of 5-years-old were shaded artificially under a relative light intensity of 5% for 70 days from August 1, and the histological changes of the terminal bud and terminally lateral bud of terminal leader and the cambial zone of the trunk base were analyzed periodically. In shade-grown trees, cell death of the leaf primordia in a terminal bud of terminal leader was observed in one of the three samples after 56 and 70 days of shading, whereas the leaf primordia in a terminal bud of terminal leader in all open-grown trees survived until the end of the experiment. In addition, the leaf primordia of the terminally lateral buds of terminal leader retained their cell nuclei until the end of the experiment. No histological changes were observed in the cambial cells after shading, but the shade-grown trees had less cambial activity than the open-grown trees through the experiment. Strong shading appeared to inhibit the formation and survival of cells in the terminal bud of terminal leader rather than the terminally lateral buds of terminal leader and the cambium. The suppression of the terminal bud growth and elongation of the surviving lateral buds would result in an umbrella-shaped crown under shade.

Leaf shape varies markedly. Here I focus on the diversity in leaf contour, which can be considered marginal variation in curvature if we omit detailed marginal structures such as serrations. This curvature can be described by a combination of sigmoids: a curve for the apical half and a curve for the basal half connected with or without an interval. Marginal curvature is determined by the position of the leaf meristem, the acceleration and deceleration of cell proliferation in the leaf meristem, and the angle of directed cell proliferation. Several key factors contributing to this variation have been revealed to date, but the majority of the underlying genetic mechanisms are unclear. Here I provide an overview of current knowledge and propose future directions for the field., (Copyright © 2017. Published by Elsevier Ltd.)

The grass inflorescence is striking not only for its beauty and diversity, but also for its developmental complexity. While models of inflorescence architecture have been proposed in both eudicots and grasses, these are inadequate to fully explain the complex branching events that occur during the development of the grass inflorescence. Key to understanding grass inflorescence architecture is the meristem determinacy/indeterminacy decision, which regulates the number of branching events that occur. Here we review what has been learned about meristem determinacy from grass mutants with defects in inflorescence development. A picture is emerging of a complex network of signaling molecules and meristem identity factors that interact to regulate inflorescence meristem activity, many of which have been modified during crop domestication directly affecting yield traits., (Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.)

In vascular plants, the root endodermis surrounds the central vasculature as a protective sheath that is analogous to the polarized epithelium in animals, and contains ring-shaped Casparian strips that restrict diffusion. After an initial lag phase, individual endodermal cells suberize in an apparently random fashion to produce 'patchy' suberization that eventually generates a zone of continuous suberin deposition. Casparian strips and suberin lamellae affect paracellular and transcellular transport, respectively. Most angiosperms maintain some isolated cells in an unsuberized state as so-called 'passage cells', which have previously been suggested to enable uptake across an otherwise-impermeable endodermal barrier. Here we demonstrate that these passage cells are late emanations of a meristematic patterning process that reads out the underlying non-radial symmetry of the vasculature. This process is mediated by the non-cell-autonomous repression of cytokinin signalling in the root meristem, and leads to distinct phloem- and xylem-pole-associated endodermal cells. The latter cells can resist abscisic acid-dependent suberization to produce passage cells. Our data further demonstrate that, during meristematic patterning, xylem-pole-associated endodermal cells can dynamically alter passage-cell numbers in response to nutrient status, and that passage cells express transporters and locally affect the expression of transporters in adjacent cortical cells.

SEPALLATA ( SEP )-like genes, which encode a subfamily of MADS-box transcription factors, are essential for specifying floral organ and meristem identity in angiosperms. Rice ( Oryza sativa ) has five SEP -like genes with partial redundancy and overlapping expression domains, yet their functions and evolutionary conservation are only partially known. Here, we describe the biological role of one of the SEP genes of rice, OsMADS5 , in redundantly controlling spikelet morphogenesis. OsMADS5 belongs to the conserved LOFSEP subgroup along with OsMADS1 and OsMADS34 OsMADS5 was expressed strongly across a broad range of reproductive stages and tissues. No obvious phenotype was observed in the osmads5 single mutants when compared with the wild type, which was largely due to the functional redundancy among the three LOFSEP genes. Genetic and molecular analyses demonstrated that OsMADS1 , OsMADS5 , and OsMADS34 together regulate floral meristem determinacy and specify the identities of spikelet organs by positively regulating the other MADS-box floral homeotic genes. Experiments conducted in yeast also suggested that OsMADS1, OsMADS5, and OsMADS34 form protein-protein interactions with other MADS-box floral homeotic members, which seems to be a typical, conserved feature of plant SEP proteins., (© 2018 American Society of Plant Biologists. All Rights Reserved.)

Stem cells must balance self-renewal and differentiation; thus, their activities are precisely controlled. In plants, the control circuits that underlie division and differentiation within meristems have been well studied, but those that underlie feedback on meristems from lateral organs remain largely unknown. Here we show that long-distance auxin transport mediates this feedback in a non-cell-autonomous manner. A low-auxin zone is associated with the shoot apical meristem (SAM) organization center, and auxin levels negatively affect SAM size. Using computational model simulations, we show that auxin transport from lateral organs can inhibit auxin transport from the SAM through an auxin transport switch and thus maintain SAM auxin homeostasis and SAM size. Genetic and microsurgical analyses confirmed the model's predictions. In addition, the model explains temporary change in SAM size of yabby mutants. Our study suggests that the canalization-based auxin flux can be widely adapted as a feedback control mechanism in plants., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Plant postembryonic development takes place in region called meristems that represent a reserve of undifferentiated cells. In the root meristem of Arabidopsis thaliana, all tissues originate from a stem-cell niche. Stem-cell daughters undergo a finite number of cell divisions until they reach the transition zone where divisions cease and cells start to differentiate. For meristem maintenance, and therefore continuous root growth, the rate of cell differentiation must equal the rate of generation of new cells. How this balance is achieved is a central question in plant biology. In this chapter we described protocols to help the operator in approaching developmental studies on the Arabidopsis root meristem.

The maize tassel represents an indeterminate male inflorescence. The number of primordia that a given inflorescence meristem produces is related to its determinacy, i.e., capacity for continued meristem activity. Transcription factors (TFs) controlling determinacy in tassel axillary meristems are well studied in maize, and small RNAs are known to influence tassel development by repressing targets, including tassel-related TFs. As core components of the RNA-inducible silence complex (RISC), Argonaute (AGO) proteins are required for small RNA-mediated repression. Here, we characterized the biological function of AGO18b, a tassel-enriched AGO. The abundance of AGO18b transcripts gradually increased during tassel development from inception to gametogenesis and were enriched in the inflorescence meristem and axillary meristems of the tassel. Repressing AGO18b expression resulted in more spikelets, which contributed to a longer central spike of the tassel. Additionally, the transcripts of several HD-ZIP III TFs that were canonical targets of microRNA166 (miR166) accumulated in the AGO18b-repressed lines. We propose that AGO18b is a negative regulator of the determinacy of inflorescence and axillary meristems, and that it acts by interacting with the miR166-HD-ZIP III TF regulatory pathway., (© 2017 Institute of Botany, Chinese Academy of Sciences.)

Protein farnesylation is central to molecular cell biology. In plants, protein farnesyl transferase mutants are pleiotropic and exhibit defective meristem organization, hypersensitivity to the hormone abscisic acid, and increased drought resistance. The precise functions of protein farnesylation in plants remain incompletely understood because few relevant farnesylated targets have been identified. Here, we show that defective farnesylation of a single factor-heat-shock protein 40 (HSP40), encoded by the J2 and J3 genes-is sufficient to confer ABA hypersensitivity, drought resistance, late flowering, and enlarged meristems, indicating that altered function of chaperone client proteins underlies most farnesyl transferase mutant phenotypes. We also show that expression of an abiotic stress-related microRNA (miRNA) regulon controlled by the transcription factor SPL7 requires HSP40 farnesylation. Expression of a truncated SPL7 form mimicking its activated proteolysis fragment of the membrane-bound SPL7 precursor partially restores accumulation of SPL7-dependent miRNAs in farnesyl transferase mutants. These results implicate the pathway directing SPL7 activation from its membrane-bound precursor as an important target of farnesylated HSP40, consistent with our demonstration that HSP40 farnesylation facilitates its membrane association. The results also suggest that altered gene regulation via select miRNAs contributes to abiotic stress-related phenotypes of farnesyl transferase mutants., (© 2017 Barghetti et al.; Published by Cold Spring Harbor Laboratory Press.)

Background and Aims: The shoot apical meristem (SAM) is the key organizing element in the plant body and is responsible for the core of plant body organization and shape. Surprisingly, there are almost no comparative data that would show links between parameters of the SAM and whole-plant traits as drivers of the plant's response to the environment., Methods: Interspecific differences in SAM anatomy were examined in 104 perennial herbaceous angiosperms., Key Results: There were differences in SAM parameters among individual species, their phylogenetic patterns, and how their variation is linked to variation in plant above-ground organs and hence species' environmental niches. SAM parameters were correlated with the size-related traits of leaf area, seed mass and stem diameter. Of the two key SAM parameters (cell size and number), variation in all organ traits was linked more strongly to cell number, with cell size being important only for seed mass. Some of these correlations were due to shared phylogenetic history (e.g. SAM diameter versus stem diameter), whereas others were due to parallel evolution (e.g. SAM cell size and seed mass)., Conclusion: These findings show that SAM parameters provide a functional link among sizes and numbers of plant organs, constituting species' environmental responses., (© The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com)

Contents 367 I. 367 II. 368 III. 370 IV. 371 371 References 371 SUMMARY: A central goal of evo-devo is to understand how morphological diversity arises from existing developmental mechanisms, requiring a clear, predictive explanatory framework of the underlying developmental mechanisms. Despite an ever-increasing literature on genes regulating grass inflorescence development, an effective model of inflorescence patterning is lacking. I argue that the existing framework for grass inflorescence development, which invokes homeotic shifts in multiple distinct meristem identities, obscures a recurring theme emerging from developmental genetic studies in grass models, that is that inflorescence branching is regulated by novel localized signaling centers. Understanding the origin and function of these novel signaling centers will be key to future evo-devo work on the grass inflorescence., (© 2017 The Author. New Phytologist © 2017 New Phytologist Trust.)

The developmental hourglass model has its foundations in classic anatomical studies by von Baer and Haeckel. In this context, even the conservation of animal body plans has been explained by evolutionary constraints acting on mid-embryogenic development. Recent studies have shown that developmental hourglass patterns also exist on the transcriptomic level, mirroring the corresponding morphological patterns. The identification of similar patterns in embryonic, post-embryonic, and life cycle spanning transcriptomes in plant and fungus development, however, contradict the notion of a direct coupling between morphological and molecular patterns. To explain the existence of hourglass patterns across kingdoms and developmental processes, we propose the organizational checkpoint model that integrates the developmental hourglass model into a framework of transcriptome switches., (Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Increased soil strength due to soil compaction or soil drying is a major limitation to root growth and crop productivity. Roots need to exert higher penetration force, resulting in increased penetration stress when elongating in soils of greater strength. This study aimed to quantify how the genotypic diversity of root tip geometry and root diameter influences root elongation under different levels of soil strength and to determine the extent to which roots adjust to increased soil strength. Fourteen wheat ( Triticum aestivum ) varieties were grown in soil columns packed to three bulk densities representing low, moderate, and high soil strength. Under moderate and high soil strength, smaller root tip radius-to-length ratio was correlated with higher genotypic root elongation rate, whereas root diameter was not related to genotypic root elongation. Based on cavity expansion theory, it was found that smaller root tip radius-to-length ratio reduced penetration stress, thus enabling higher root elongation rates in soils with greater strength. Furthermore, it was observed that roots could only partially adjust to increased soil strength. Root thickening was bounded by a maximum diameter, and root tips did not become more acute in response to increased soil strength. The obtained results demonstrated that root tip geometry is a pivotal trait governing root penetration stress and root elongation rate in soils of greater strength. Hence, root tip shape needs to be taken into account when selecting for crop varieties that may tolerate high soil strength., (© 2017 American Society of Plant Biologists. All Rights Reserved.)

Sclereids are a fundamental cell type that widely exist in higher plants and are generally thought to have a mechanical function. However, the occurrence of sclereids in the ephemeral corolla has rarely been documented and their biological significance is poorly understood. In this study, flower buds from Camellia sinensis at various ontogenetic stages were sampled, cleared, sectioned, stained, and examined using light microscopy to ascertain the morphology and distribution of sclereids and their variation. In addition, Camellia japonica plants with distinctive floral structures were investigated and compared to explore whether sclereid occurrence is associated with floral form. In particular, a computational simulation using finite element analysis was undertaken to investigate how corollas, with and without sclereids, responded to wind and rain. The results showed that sclereids have some mechanical properties that are based on their shape and distribution, which make the soft corolla strong enough to protect the inner ovary. Thus, corolla sclereids may explain how the seemingly delicate corolla performs its protective function in response to environmental stresses. These findings provide further evidence for the hypothesis that flower traits exhibit adaptive responses to abiotic factors in addition to their traditionally recognized pollinator-mediated selection.

Premise of the Study: Pentaclethra and Dimorphandra (Leguminosae) have long been considered a possible enigmatic link between caesalpinioids and mimosoids because they both have an imbricate calyx and heteromorphic androecium, floral features that are rare among mimosoids but common among caesalpinioids. This study compared the developing flowers of Dimorphandra mollis and Pentaclethra macroloba to determine whether the shared floral conditions also have the same ontogenetic origin., Methods: Buds of different sizes and flowers were processed for surface (scanning electron microscopy) and histological (light microscopy) examination., Key Results: The floral meristem initiates five sepal primordia in a modified helical order in both species. The median sagittal sepal is adaxial. The overlap of the sepals during elongation culminates with the formation of the imbricate calyx. Heteromorphic androecia arise in the intermediate stages of development. In P. macroloba , the fertile pollen-bearing stamens are antesepalous, robust and short, and the anthers carry a robust apical gland; the staminodes are long and white with a vestigial apical gland. In contrast, in D. mollis the fertile pollen-bearing stamens are antepetalous without glands and as long as the staminodes. The staminodes are thinner with an expanded apical region., Conclusions: The imbricate calyx and the heteromorphic androecium in the studied species originated via distinct pathways, favoring the hypothesis of homoplasy of these conditions. The pathways observed in P. macroloba are more similar to those observed in caesalpinioids than to those observed in mimosoids, indicating that although the floral development differs between the species studied, it supports the basal placement of Pentaclethra among mimosoids., (© 2017 Botanical Society of America.)

Enhanced superoxide generation and significant inhibition of succinate dehydrogenase (SDH) activity followed by a strong reduction of root growth were detected in barley seedlings exposed to a 5μM Hg concentration for 30min, which increased further in an Hg dose-dependent manner. While at a 25μM Hg concentration no cell death was detectable, a 50μM Hg treatment triggered cell death in the root meristematic zone, which was markedly intensified after the treatment of roots with 100μM Hg and was detectable in the whole root tips. Generation of superoxide and H 2 O 2 was a very rapid response of root tips occurring even after 5min of exposure to Hg. Application of an NADPH oxidase inhibitor or the inhibition of electron flow in mitochondria by the inhibition of complex I did not influence the Hg-induced H 2 O 2 production. Treatment of roots with thenoyltrifluoroacetone, a non-competitive inhibitor of SDH, markedly reduced root growth and induced both superoxide and H 2 O 2 production in a dose dependent manner. Similar to results obtained in intact roots, Hg strongly inhibited SDH activity in the crude mitochondrial fraction and caused a considerable increase of superoxide production, which was markedly reduced by the competitive inhibitors of SDH. These results indicate that the mitochondrial complex II-derived superoxide is the primary source of Hg toxicity in the barley root tip., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Environmental gravity modulates plant growth and development, and these processes are influenced by the balance between cell proliferation and differentiation in meristems. Meristematic cells are characterized by the coordination between cell proliferation and cell growth, that is, by the accurate regulation of cell cycle progression and the optimal production of biomass for the viability of daughter cells after division. Thus, cell growth is correlated with the rate of ribosome biogenesis and protein synthesis. We investigated the effects of simulated microgravity on cellular functions of the root meristem in a sequential study. Seedlings were grown in a clinostat, a device producing simulated microgravity, for periods between 3 and 10days. In a complementary study, seedlings were grown in a Random Positioning Machine (RPM) and sampled sequentially after similar periods of growth. Under these conditions, the cell proliferation rate and the regulation of cell cycle progression showed significant alterations, accompanied by a reduction of cell growth. However, the overall size of the root meristem did not change. Analysis of cell cycle phases by flow cytometry showed changes in their proportion and duration, and the expression of the cyclin B1 gene, a marker of entry in mitosis, was decreased, indicating altered cell cycle regulation. With respect to cell growth, the rate of ribosome biogenesis was reduced under simulated microgravity, as shown by morphological and morphometric nucleolar changes and variations in the levels of the nucleolar protein nucleolin. Furthermore, in a nucleolin mutant characterized by disorganized nucleolar structure, the microgravity treatment intensified disorganization. These results show that, regardless of the simulated microgravity device used, a great disruption of meristematic competence was the first response to the environmental alteration detected at early developmental stages. However, longer periods of exposure to simulated microgravity do not produce an intensification of the cellular damages or a detectable developmental alteration in seedlings analyzed at further stages of their growth. This suggests that the secondary response to the gravity alteration is a process of adaptation, whose mechanism is still unknown, which eventually results in viable adult plants., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Key Message: Selenite oppositely modifies cytokinin and nitric oxide metabolism in Arabidopsis organs. A mutually negative interplay between the molecules exists in selenite-exposed roots; and their overproduction causes selenite insensitivity. Selenium-induced phytotoxicity is accompanied by developmental alterations such as primary root (PR) shortening. Growth changes are provoked by the modulation of hormone status and signalling. Cytokinin (CK) cooperates with the nitric oxide (NO) in many aspects of plant development; however, their interaction under abiotic stress has not been examined. Selenite inhibited the growth of Arabidopsis seedlings and reduced root meristem size through cell division arrest. The CK-dependent pARR5::GUS activity revealed the intensification of CK signalling in the PR tip, which may be partly responsible for the root meristem shortening. The selenite-induced alterations in the in situ expressions of cytokinin oxidases (AtCKX4::GUS, AtCKX5::GUS) are associated with selenite-triggered changes of CK signalling. In wild-type (WT) and NO-deficient nia1nia2 root, selenite led to the diminution of NO content, but CK overproducer ipt-161 and -deficient 35S:CKX2 roots did not show NO decrease. Exogenous NO (S-nitroso-N-acetyl-DL-penicillamine, SNAP) reduced the pARR5::GFP and pTCS::GFP expressions. Roots of the 35S:CKX and cyr1 plants suffered more severe selenite-triggered viability loss than the WT, while in ipt-161 and gsnor1-3 no obvious viability decrease was observed. Exogenous NO ameliorated viability loss, but benzyladenine intensified it. Based on the results, selenite impacts development by oppositely modifying CK signalling and NO level. In the root system, CK signalling intensifies which possibly contributes to the nitrate reductase-independent NO diminution. A mutually negative CK-NO interplay exists in selenite-exposed roots; however, overproduction of both molecules worsens selenite sensing. Hereby, we suggest novel regulatory interplay and role for NO and CK in abiotic stress signalling.

A Carboniferous root apex reiterates the importance of the fossil record and classic developmental plant anatomy for modern evo-devo perspectives on plant diversity and evolution., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Differentiation and morphogenetic processes during plant development are particularly robust. At the cellular level, however, plants also show great plasticity in response to environmental conditions, and can even reverse apparently terminal differentiated states with remarkable ease. Can we understand and predict both robust and plastic systemic responses as a general consequence of the non-trivial interplay between intracellular regulatory networks, extrinsic environmental signalling, and tissue-level mechanical constraints? Flower development has become an ideal model system to study these general questions of developmental biology, which are especially relevant to understanding stem cell patterning in plants, animals, and human disease. Decades of detailed study of molecular developmental genetics, as well as novel experimental techniques for in vivo assays in both wild-type and mutant plants, enable the postulation and testing of experimentally grounded mathematical and computational network dynamical models. Research in our group aims to explain the emergence of robust transitions that occur at the shoot apical meristem, as well as flower development, as the result of the collective action of key molecular components in regulatory networks subjected to intra-organismal signalling and extracellular constraints. Here we present a brief overview of recent work from our group, and that of others, focusing on the use of simple dynamical models to address cell-fate specification and cell-state stochastic dynamics during flowering transition and cell-state transitions at the shoot apical meristem of Arabidopsis thaliana. We also focus on how our work fits within the general field of plant developmental modelling, which is being developed by many others., (© The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Wheat grain yield consists of three components: spikes per plant, grains per spike (i.e. head or ear), and grain weight; and the grains per spike can be dissected into two subcomponents: spikelets per spike and grains per spikelet. An increase in any of these components will directly contribute to grain yield. Wheat morphology biology tells that a wheat plant has no lateral meristem that forms any branching shoot or spike. In this study, we report two novel shoot and spike traits that were produced from lateral meristems in bread wheat. One is supernumerary shoot that was developed from an axillary bud at the axil of leaves on the elongated internodes of the main stem. The other is supernumerary spike that was generated from a spikelet meristem on a spike. In addition, supernumerary spikelets were generated on the same rachis node of the spike in the plant that had supernumerary shoot and spikes. All of these supernumerary shoots/spikes/spikelets found in the super wheat plants produced normal fertility and seeds, displaying huge yield potential in bread wheat.

Root traits in morphology, chemistry and anatomy are important to root physiological functions, but the differences between shallow and deep roots have rarely been studied in woody plants. Here, we selected three temperate hardwood species, Juglans mandshurica Maxim., Fraxinus mandschurica Rupr. and Phellodendron amurense Rupr., in plantations in northeastern China and measured morphological, anatomical and chemical traits of root tips (i.e., the first-order roots) at surface (0-10 cm) and subsurface (20-30 cm) soil layers. The objectives of this study were to identify how those traits changed with soil depth and to reveal potential functional differences. The results showed that root diameters in deep root tips were greater in J. mandshurica and F. mandschurica, but smaller in P. amurense. However, root stele diameter and the ratio of stele to root diameter in the subsurface layer were consistently greater in all three species, which may enhance their abilities to penetrate into soil. All deep roots exhibited lower tissue nitrogen concentration and respiration rate, which were possibly caused by lower nutrient availability in the subsurface soil layer. Significant differences between shallow and deep roots were observed in xylem structure, with deep roots having thicker stele, wider maximum conduit and greater number of conduits per stele. Compared with shallow roots, the theoretical hydraulic conductivities in deep roots were enhanced by 133% (J. mandshurica), 78% (F. mandschurica) and 217% (P. amurense), respectively, indicating higher efficiency of transportation. Our results suggest that trees' root tip anatomical structure and physiological activity vary substantially with soil environment., (© The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Main Conclusion: The T-DNA 6b oncogene induces complex and partly unprecedented phenotypic changes in tobacco stems and leaves, which result from hypertrophy and hyperplasia with ectopic spot-like, ridge-like and sheet-like meristems. The Agrobacterium T-DNA oncogene 6b causes complex growth changes in tobacco including enations; this unusual phenotype has been called "6b enation syndrome". A detailed morphological and anatomical analysis of the aerial part of Nicotiana tabacum plants transformed with a dexamethasone-inducible dex-T-6b gene revealed several striking growth phenomena. Among these were: uniform growth of ectopic photosynthetic cells on the abaxial leaf side, gutter-like petioles with multiple parallel secondary veins, ectopic leaf primordia emerging behind large glandular trichomes, corniculate structures emerging from distal ends of secondary veins, pin-like structures with remarkable branching patterns, ectopic vascular strands in midveins and petioles extending down along the stem, epiascidia and hypoascidia, double enations and complete inhibition of leaf outgrowth. Ectopic stipule-like leaves and inverted leaves were found at the base of the petioles. Epinastic and hyponastic growth of petioles and midveins yielded complex but predictable leaf folding patterns. Detailed anatomical analysis of over sixty different 6b-induced morphological changes showed that the different modifications are derived from hypertrophy and abaxial hyperplasia, with ectopic photosynthetic cells forming spot-like, ridge-like and sheet-like meristems and ectopic vascular strands forming regular patterns in midveins, petioles and stems. Part of the enation syndrome is due to an unknown phloem-mobile enation factor. Graft experiments showed that the 6b mRNA is mobile and could be the enation factor. Our work provides a better insight in the basic effects of the 6b oncogene.

Plants sense the foliar shade of competitors and alter their developmental programs through the shade-avoidance response. Internode and petiole elongation, and changes in overall leaf area and leaf mass per area, are the stereotypical architectural responses to foliar shade in the shoot. However, changes in leaf shape and complexity in response to shade remain incompletely, and qualitatively, described. Using a meta-analysis of more than 18,000 previously published leaflet outlines, we demonstrate that shade avoidance alters leaf shape in domesticated tomato (Solanum lycopersicum) and wild relatives. The effects of shade avoidance on leaf shape are subtle with respect to individual traits but are combinatorially strong. We then seek to describe the developmental origins of shade-induced changes in leaf shape by swapping plants between light treatments. Leaf size is light responsive late into development, but patterning events, such as stomatal index, are irrevocably specified earlier. Observing that shade induces increases in shoot apical meristem size, we then describe gene expression changes in early leaf primordia and the meristem using laser microdissection. We find that in leaf primordia, shade avoidance is not mediated through canonical pathways described in mature organs but rather through the expression of KNOTTED1-LIKE HOMEOBOX and other indeterminacy genes, altering known developmental pathways responsible for patterning leaf shape. We also demonstrate that shade-induced changes in leaf primordium gene expression largely do not overlap with those found in successively initiated leaf primordia, providing evidence against classic hypotheses that shaded leaf morphology results from the prolonged production of juvenile leaf types., (© 2015 American Society of Plant Biologists. All Rights Reserved.)

Background: We reported previously that root elongation in Arabidopsis is promoted by exogenous proline, raising the possibility that this amino acid may modulate root growth., Results: To evaluate this hypothesis we used a combination of genetic, pharmacological and molecular analyses, and showed that proline specifically affects root growth by modulating the size of the root meristem. The effects of proline on meristem size are parallel to, and independent from, hormonal pathways, and do not involve the expression of genes controlling cell differentiation at the transition zone. On the contrary, proline appears to control cell division in early stages of postembryonic root development, as shown by the expression of the G2/M-specific CYCLINB1;1 (CYCB1;1) gene., Conclusions: The overall data suggest that proline can modulate the size of root meristematic zone in Arabidopsis likely controlling cell division and, in turn, the ratio between cell division and cell differentiation.

Early vigour of rice, defined as seedling capacity to accumulate shoot dry weight (SDW) rapidly, is a complex trait. It depends on a genotype propensity to assimilate, store, and/or use non-structural carbohydrates (NSC) for producing large and/or numerous leaves, involving physiological trade-offs in the expression of component traits and, possibly, physiological and genetic linkages. This study explores a plant-model-assisted phenotyping approach to dissect the genetic architecture of rice early vigour, applying the Genome Wide Association Study (GWAS) to morphological and NSC measurements, as well as fitted parameters for the functional-structural plant model, Ecomeristem. Leaf size, number, SDW, and source-leaf NSC concentration were measured on a panel of 123 japonica accessions. The data were used to estimate Ecomeristem genotypic parameters driving organ appearance rate, size, and carbon dynamics. GWAS was performed based on 12 221 single-nucleotide polymorphisms (SNP). Twenty-three associations were detected at P <1×10(-4) and 64 at P <5×10(-4). Associations for NSC and model parameters revealed new regions related to early vigour that had greater significance than morphological traits, providing additional information on the genetic control of early vigour. Plant model parameters were used to characterize physiological and genetic trade-offs among component traits. Twelve associations were related to loci for cloned genes, with nine related to organogenesis, plant height, cell size or cell number. The potential use of these associations as markers for breeding is discussed., (© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Growing agricultural demands in the face of impending inorganic phosphate (Pi) shortages underscore a need for a better understanding of plant development under conditions of Pi deprivation. Pi is an essential nutrient that is a major component of fertilizer. Plants have evolved strategies to improve the acquisition of this nutrient by altering root development under shortage conditions. We show that signaling peptides thought to act redundantly in Arabidopsis thaliana development have distinct functions in response to Pi deprivation. Using microscopy and confocal imaging, roots were analyzed for growth rate and cellular composition. Using expression microarrays, genes influencing development in response to phosphate deprivation were identified. ROOT GROWTH FACTOR1 (RGF1) and RGF2 influenced different aspects of root development under conditions of Pi deprivation. We found that RGF2 influenced the longitudinal growth rate in the primary root in response to Pi deprivation, whereas RGF1 affected circumferential cell number in the root meristem. These data suggest that the mechanisms controlling adaptive development can depend on disparate functions of genes thought to act redundantly, thus elucidating new functions for important developmental regulators., (© 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.)

How organisms determine particular organ numbers is a fundamental key to the development of precise body structures; however, the developmental mechanisms underlying organ-number determination are unclear. In many eudicot plants, the primordia of sepals and petals (the floral organs) first arise sequentially at the edge of a circular, undifferentiated region called the floral meristem, and later transition into a concentric arrangement called a whorl, which includes four or five organs. The properties controlling the transition to whorls comprising particular numbers of organs is little explored. We propose a development-based model of floral organ-number determination, improving upon earlier models of plant phyllotaxis that assumed two developmental processes: the sequential initiation of primordia in the least crowded space around the meristem and the constant growth of the tip of the stem. By introducing mutual repulsion among primordia into the growth process, we numerically and analytically show that the whorled arrangement emerges spontaneously from the sequential initiation of primordia. Moreover, by allowing the strength of the inhibition exerted by each primordium to decrease as the primordium ages, we show that pentamerous whorls, in which the angular and radial positions of the primordia are consistent with those observed in sepal and petal primordia in Silene coeli-rosa, Caryophyllaceae, become the dominant arrangement. The organ number within the outmost whorl, corresponding to the sepals, takes a value of four or five in a much wider parameter space than that in which it takes a value of six or seven. These results suggest that mutual repulsion among primordia during growth and a temporal decrease in the strength of the inhibition during initiation are required for the development of the tetramerous and pentamerous whorls common in eudicots.