Floral Meristem Research Articles

Characterization of Two AGAMOUS-like Genes and Their Promoters from the Cymbidium faberi (Orchidaceae).

Arabidopsis AGAMOUS (AG) play roles in determining stamens' and carpels' identities, floral meristem determinacy, and repression of the A-function. Gynostemium fused by stamens and carpels is a characteristic reproductive structure in orchid flowers, which shows a considerable difference from the reproductive organs of eudicots and other monocot species. The molecular basis of orchid gynostemium development remains largely unknown. Here, we report the identification and functional characterization of two AG-like genes, CyfaAG1 and CyfaAG2, and their promoters from C. faberi. Both CyfaAG1 and CyfaAG2 are highly expressed in the anther cap, gynostemium, and ovary. Ectopic expression of CyfaAG1 and CyfaAG2 promotes early flowering of wild-type Arabidopsis. Moreover, ectopic expression of CyfaAG1 completely rescues floral defects in the Arabidopsis ag-1 mutant, while ectopic expression of CyfaAG2 only completes filament and carpel development. Our findings suggest that CyfaAG1 acts as an evolutionarily conserved C-function gene in determining reproductive organ identity and mediating floral meristem determinacy. CyfaAG2 redundantly mediates the C-function in floral meristem determinacy and gynostemium development. Our results provided more details to understand how the C-class function has been partitioned in orchids, and the roles of two AG orthologs in regulating gynostemium development in C. faberi.

BSA-Seq and Transcriptomic Analysis Provide Candidate Genes Associated with Inflorescence Architecture and Kernel Orientation by Phytohormone Homeostasis in Maize.

The developmental plasticity of the maize inflorescence depends on meristems, which directly affect reproductive potential and yield. However, the molecular roles of upper floral meristem (UFM) and lower floral meristem (LFM) in inflorescence and kernel development have not been fully elucidated. In this study, we characterized the reversed kernel1 (rk1) novel mutant, which contains kernels with giant embryos but shows normal vegetative growth like the wild type (WT). Total RNA was extracted from the inflorescence at three stages for transcriptomic analysis. A total of 250.16-Gb clean reads were generated, and 26,248 unigenes were assembled and annotated. Gene ontology analyses of differentially expressed genes (DEGs) detected in the sexual organ formation stage revealed that cell differentiation, organ development, phytohormonal responses and carbohydrate metabolism were enriched. The DEGs associated with the regulation of phytohormone levels and signaling were mainly expressed, including auxin (IAA), jasmonic acid (JA), gibberellins (GA), and abscisic acid (ABA). The transcriptome, hormone evaluation and immunohistochemistry observation revealed that phytohormone homeostasis were affected in rk1. BSA-Seq and transcriptomic analysis also provide candidate genes to regulate UFM and LFM development. These results provide novel insights for understanding the regulatory mechanism of UFM and LFM development in maize and other plants.

Introducing MdTFL1 Promotes Heading Date and Produces Semi-Draft Phenotype in Rice.

Flowering time (in rice, termed the heading date), plant height, and grain number are crucial agronomic traits for rice productivity. The heading date is controlled via environmental factors (day length and temperature) and genetic factors (floral genes). TERMINAL FLOWER 1 (TFL1) encodes a protein that controls meristem identity and participates in regulating flowering. In this study, a transgenic approach was used to promote the heading date in rice. We isolated and cloned apple MdTFL1 for early flowering in rice. Transgenic rice plants with antisense MdTFL1 showed an early heading date compared with wild-type plants. A gene expression analysis suggested that introducing MdTFL1 upregulated multiple endogenous floral meristem identity genes, including the (early) heading date gene family FLOWERING LOCUS T and MADS-box transcription factors, thereby shortening vegetable development. Antisense MdTFL1 also produced a wide range of phenotypic changes, including a change in overall plant organelles that affected an array of traits, especially grain productivity. The transgenic rice exhibited a semi-draft phenotype, increased leaf inclination angle, restricted flag leaf length, reduced spikelet fertility, and fewer grains per panicle. MdTFL1 plays a central role in regulating flowering and in various physiological aspects. These findings emphasize the role of TFL1 in regulating flowering in shortened breeding and expanding its function to produce plants with semi-draft phenotypes.

How flower development genes were identified using forward genetic screens in Arabidopsis thaliana.

In the later part of the 1980s, the time was ripe for identifying genes controlling flower development. In that pregenomic era, the easiest way to do this was to induce random mutations in seeds by chemical mutagens (or irradiation) and to screen thousands of plants for those with phenotypes specifically defective in floral morphogenesis. Here, we discuss the results of premolecular screens for flower development mutants in Arabidopsis thaliana, carried out at Caltech and Monash University, emphasizing the usefulness of saturation mutagenesis, multiple alleles to identify full loss-of-function, conclusions based on multiple mutant analyses, and from screens for enhancer and suppressor modifiers of original mutant phenotypes. One outcome was a series of mutants that led to the ABC floral organ identity model (AP1, AP2, AP3, PI, and AG). In addition, genes controlling flower meristem identity (AP1, CAL, and LFY), floral meristem size (CLV1 and CLV3), development of individual floral organ types (CRC, SPT, and PTL), and inflorescence meristem properties (TFL1, PIN1, and PID) were defined. These occurrences formed targets for cloning that eventually helped lead to an understanding of transcriptional control of the identity of floral organs and flower meristems, signaling within meristems, and the role of auxin in initiating floral organogenesis. These findings in Arabidopsis are now being applied to investigate how orthologous and paralogous genes act in other flowering plants, allowing us to wander in the fertile fields of evo-devo.

LEAFY and APETALA1 down-regulate ZINC FINGER PROTEIN 1 and 8 to release their repression on class B and C floral homeotic genes

Organ initiation from the shoot apical meristem first gives rise to leaves during vegetative development and then flowers during reproductive development. LEAFY (LFY) is activated after floral induction and together with other factors promotes the floral program. LFY functions redundantly with APETALA1 (AP1) to activate the class B genes APETALA3 (AP3) and PISTILLATA (PI), the class C gene AGAMOUS (AG), and the class E gene SEPALLATA3, which leads to the specification of stamens and carpels, the reproductive organs of flowers. Molecular and genetic networks that control the activation of AP3, PI, and AG in flowers have been well studied; however, much less is known about how these genes are repressed in leaves and how their repression is lifted in flowers. Here, we showed that two genes encoding Arabidopsis C2H2 ZINC FINGER PROTEIN (ZFP) transcription factors, ZP1 and ZFP8, act redundantly to directly repress AP3, PI, and AG in leaves. After LFY and AP1 are activated in floral meristems, they down-regulate ZP1 and ZFP8 directly to lift the repression on AP3, PI, and AG. Our results reveal a mechanism for how floral homeotic genes are repressed and derepressed before and after floral induction.

AGAMOUS regulates various target genes via cell cycle-coupled H3K27me3 dilution in floral meristems and stamens.

The MADS domain transcription factor AGAMOUS (AG) regulates floral meristem termination by preventing maintenance of the histone modification lysine 27 of histone H3 (H3K27me3) along the KNUCKLES (KNU) coding sequence. At 2 d after AG binding, cell division has diluted the repressive mark H3K27me3, allowing activation of KNU transcription prior to floral meristem termination. However, how many other downstream genes are temporally regulated by this intrinsic epigenetic timer and what their functions are remain unknown. Here, we identify direct AG targets regulated through cell cycle-coupled H3K27me3 dilution in Arabidopsis thaliana. Expression of the targets KNU, AT HOOK MOTIF NUCLEAR LOCALIZED PROTEIN18 (AHL18), and PLATZ10 occurred later in plants with longer H3K27me3-marked regions. We established a mathematical model to predict timing of gene expression and manipulated temporal gene expression using the H3K27me3-marked del region from the KNU coding sequence. Increasing the number of del copies delayed and reduced KNU expression in a polycomb repressive complex 2- and cell cycle-dependent manner. Furthermore, AHL18 was specifically expressed in stamens and caused developmental defects when misexpressed. Finally, AHL18 bound to genes important for stamen growth. Our results suggest that AG controls the timing of expression of various target genes via cell cycle-coupled dilution of H3K27me3 for proper floral meristem termination and stamen development.

The Secrets of Meristems Initiation: Axillary Meristem Initiation and Floral Meristem Initiation.

The branching phenotype is an extremely important agronomic trait of plants, especially for horticultural crops. It is not only an important yield character of fruit trees, but also an exquisite ornamental trait of landscape trees and flowers. The branching characteristics of plants are determined by the periodic initiation and later development of meristems, especially the axillary meristem (AM) in the vegetative stage and the floral meristem (FM) in the reproductive stage, which jointly determine the above-ground plant architecture. The regulation of meristem initiation has made great progress in model plants in recent years. Meristem initiation is comprehensively regulated by a complex regulatory network composed of plant hormones and transcription factors. However, as it is an important trait, studies on meristem initiation in horticultural plants are very limited, and the mechanism of meristem initiation regulation in horticultural plants is largely unknown. This review summarizes recent research advances in axillary meristem regulation and mainly reviews the regulatory networks and mechanisms of AM and FM initiation regulated by transcription factors and hormones. Finally, considering the existing problems in meristem initiation studies and the need for branching trait improvement in horticulture plants, we prospect future studies to accelerate the genetic improvement of the branching trait in horticulture plants.

Changes in the expression pattern of OsWUS negatively regulate plant stature and panicle development in rice.

WUSCHEL (WUS) and WUSCHEL-RELATED HOMEOBOX (WOX) encode transcription factors and play important roles in regulating the formation and maintenance of shoot and floral meristems. OsWUS have distinct functions in meristem development with slightly tuned expression. However, the mechanisms regulating the specific expression of OsWUS need to be further explored. In this study, an abnormal expression mutant of OsWUS, called Dwarf and aberrant panicle 1 (Dap1) was used. In order to identify the causal gene in Dap1, high-efficiency thermal asymmetric interlaced (hiTAIL)-PCR and co-segregation analysis were performed. We surveyed the growth and yield traits in Dap1 and wild type. Changes in gene expression between Dap1 and wild type were determined by RNA-seq. The Dap1 mutant is due to the T-DNA inserted at 3,628-bp upstream of the translation start codon of OsWUS. Plant height, tiller numbers, panicle length, the number of grains per main panicle, and the number of secondary branches was significantly reduced in the Dap1 mutant. The expression of OsWUS was markedly increased in Dap1 mutant plants compared to the wild type, which might be due to a disruption in the genomic sequence integrity. Simultaneously, the expression levels of gibberellic acid-related genes and genes involved in panicle development were significantly changed in the Dap1 mutant. Our results suggest that OsWUS is a precise regulatory element, its specific spatio-temporal expression pattern is critical for its function, and both loss-of-function and gain-of-function mutations lead to abnormal plant growth.

Functional Characterization of Candidate Genes, Gohir.D05G103700 and Gohir.D12G153600, Identified through Expression QTL Analysis Using Virus-Induced Gene Silencing in Upland Cotton (Gossypium hirsutum L.)

Cotton (Gossypium spp.) is a major source of natural fiber and an important cash crop. The cotton growth habit and architecture determine its productivity and influence management strategies for commercial production. The GATA transcription factors (TFs) control various developmental processes in plants, such as flower, bract and embryo development, and petal differentiation. As stable transformation is still a bottleneck in many plant species, TRV-VIGS was used to manipulate gene expression in different plants, including Gossypium hirsutum L. In this study, we undertook the TRV-based VIGS to functionally characterize two candidate genes, Gohir.D05G103700 and Gohir.D12G153600, identified through expression QTL analysis for five floral induction and meristem identity genes using the upland cotton mini-core collection. Virus-induced silencing of the Gohir.D05G103700 gene resulted in up to a 1.4-fold reduction in the transcript level in two inoculated plants, G3 and G4, and Gohir.D12G153600 gene resulted in up to a 2.3-fold reduction in transcript level in a single inoculated plant P05 relative to the mock-treated plant. The TRV2-Gohir.D05G103700-inoculated plants G3 and G4 also exhibited loss of the supernumerary (fourth) floral bract in the squares, whereas the TRV2-Gohir.D12G153600-inoculated plants did not show any observable phenotypic change relative to the mock-treated plants. Altogether, this study suggested that TRV-VIGS can be used to characterize genes in cotton relatively rapidly, and the cotton Gohir.D05G103700 gene is a positive regulator of the indeterminate growth habit in cotton, which could be manipulated to obtain a cotton plant with architecture best suited for the cultivation area.

RcSPL1-RcTAF15b regulates the flowering time of rose (Rosa chinensis).

Rose (Rosa chinensis), which is an economically valuable floral species worldwide, has three types, namely once-flowering (OF), occasional or re-blooming (OR), and recurrent or continuous flowering (CF). However, the mechanism underlying the effect of the age pathway on the duration of the CF or OF juvenile phase is largely unknown. In this study, we observed that the RcSPL1 transcript levels were substantially upregulated during the floral development period in CF and OF plants. Additionally, accumulation of RcSPL1 protein was controlled by rch-miR156. The ectopic expression of RcSPL1 in Arabidopsis thaliana accelerated the vegetative phase transition and flowering. Furthermore, the transient overexpression of RcSPL1 in rose plants accelerated flowering, whereas silencing of RcSPL1 had the opposite phenotype. Accordingly, the transcription levels of floral meristem identity genes (APETALA1, FRUITFULL, and LEAFY) were significantly affected by the changes in RcSPL1 expression. RcTAF15b protein, which is an autonomous pathway protein, was revealed to interact with RcSPL1. The silencing and overexpression of RcTAF15b in rose plants led to delayed and accelerated flowering, respectively. Collectively, the study findings imply that RcSPL1-RcTAF15b modulates the flowering time of rose plants.

Deregulation of ζ-carotene desaturase in Arabidopsis and tomato exposes a unique carotenoid-derived redundant regulation of floral meristem identity and function.

A level of redundancy and interplay among the transcriptional regulators of floral development safeguards a plant's reproductive success and ensures crop production. In the present study, an additional layer of complexity in the regulation of floral meristem (FM) identity and flower development is elucidated linking carotenoid biosynthesis and metabolism to the regulation of determinate flowering. The accumulation and subsequent cleavage of a diverse array of ζ-carotenes in the chloroplast biogenesis 5 (clb5) mutant of Arabidopsis results in the reprogramming of meristematic gene regulatory networks establishing FM identity mirroring that of the FM identity master regulator, APETALA1 (AP1). The immediate transition to floral development in clb5 requires long photoperiods in a GIGANTEA-independent manner, whereas AP1 is essential for the floral organ development of clb5. The elucidation of this link between carotenoid metabolism and floral development translates to tomato exposing a regulation of FM identity redundant to and initiated by AP1 and proposed to be dependent on the E class floral initiation and organ identity regulator, SEPALLATA3 (SEP3).

Transcriptional Regulation of Female and Male Flower Bud Initiation and Development in Pecan (Carya illinoensis)

Pecan (Carya illinoensis) nuts are delicious and rich in unsaturated fatty acids, which are beneficial for human health. Their yield is closely related to several factors, such as the ratio of female and male flowers. We sampled and paraffin-sectioned female and male flower buds for one year and determined the stages of initial flower bud differentiation, floral primordium formation, and pistil and stamen primordium formation. We then performed transcriptome sequencing on these stages. Our data analysis suggested that FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 play a role in flower bud differentiation. J3 was highly expressed in the early stage of female flower buds and may play a role in regulating flower bud differentiation and flowering time. Genes such as NF-YA1 and STM were expressed during male flower bud development. NF-YA1 belongs to the NF-Y transcription factor family and may initiate downstream events leading to floral transformation. STM promoted the transformation of leaf buds to flower buds. AP2 may have been involved in the establishment of floral meristem characteristics and the determination of floral organ characteristics. Our results lay a foundation for the control and subsequent regulation of female and male flower bud differentiation and yield improvement.

Co-regulatory effects of hormone and mRNA-miRNA module on flower bud formation of Camellia oleifera.

Few flower buds in a high-yield year are the main factors restricting the yield of Camellia oleifera in the next year. However, there are no relevant reports on the regulation mechanism of flower bud formation. In this study, hormones, mRNAs, and miRNAs were tested during flower bud formation in MY3 ("Min Yu 3," with stable yield in different years) and QY2 ("Qian Yu 2," with less flower bud formation in a high-yield year) cultivars. The results showed that except for IAA, the hormone contents of GA3, ABA, tZ, JA, and SA in the buds were higher than those in the fruit, and the contents of all hormones in the buds were higher than those in the adjacent tissues. This excluded the effect of hormones produced from the fruit on flower bud formation. The difference in hormones showed that 21-30 April was the critical period for flower bud formation in C. oleifera; the JA content in MY3 was higher than that in QY2, but a lower concentration of GA3 contributed to the formation of the C. oleifera flower bud. JA and GA3 might have different effects on flower bud formation. Comprehensive analysis of the RNA-seq data showed that differentially expressed genes were notably enriched in hormone signal transduction and the circadian system. Flower bud formation in MY3 was induced through the plant hormone receptor TIR1 (transport inhibitor response 1) of the IAA signaling pathway, the miR535-GID1c module of the GA signaling pathway, and the miR395-JAZ module of the JA signaling pathway. In addition, the expression of core clock components GI (GIGANTEA) and CO (CONSTANS) in MY3 increased 2.3-fold and 1.8-fold over that in QY2, respectively, indicating that the circadian system also played a role in promoting flower bud formation in MY3. Finally, the hormone signaling pathway and circadian system transmitted flowering signals to the floral meristem characteristic genes LFY (LEAFY) and AP1 (APETALA 1) via FT (FLOWERING LOCUS T) and SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CO 1) to regulate flower bud formation. These data will provide the basis for understanding the mechanism of flower bud alternate formation and formulating high yield regulation measures for C. oleifera.

SnRNA-seq and mRNA hybridization indicate key bud events and LcFT1 and LcTFL1-2 mRNA transportability during floral transition in litchi.

In flowering plants, floral induction signals intersect at the shoot apex to modulate meristem determinacy and growth form. Herein, we reported a snRNA-seq analysis of litchi apical buds at different developmental stages. A total of 41,641 nuclei expressing 21,402 genes were analyzed, revealing 35 cell clusters corresponding to 12 broad populations. We signature genes associated with floral transition and propose a model that profile the key events associated with litchi floral meristem identity by analyzing 567 identified floral meristem cells at single cell resolution. Interestingly, snRNA-seq data indicated that all putative FT and TFL1 genes were not expressed in bud nuclei, but significant expressions of them were detected in bud samples using RT-PCR. Based on the expression patterns and gene silencing results, we highlight the critical role of LcTFL1-2 in inhibiting flowering and propose that LcFT1/LcTFL1-2 expression ratio may determine the success flower transition. And the transport of LcFT1 and LcTFL1-2 mRNA from the leaf to the shoot apical meristem was proposed based on in-situ and dot blot hybridization results. These findings allowed for a more comprehensive understanding of the molecular events that occur during the litchi floral transition, as well as the identification of new regulators.

Antagonistic regulation of target genes by the SISTER OF TM3-JOINTLESS2 complex in tomato inflorescence branching.

Inflorescence branch number is a yield-related trait controlled by cell fate determination in meristems. Two MADS-box transcription factors (TFs)-SISTER OF TM3 (STM3) and JOINTLESS 2 (J2)-have opposing regulatory roles in inflorescence branching. However, the mechanisms underlying their regulatory functions in inflorescence determinacy remain unclear. Here, we characterized the functions of these TFs in tomato (Solanum lycopersicum) floral meristem and inflorescence meristem (IM) through chromatin immunoprecipitation and sequencing analysis of their genome-wide occupancy. STM3 and J2 activate or repress the transcription of a set of common putative target genes, respectively, through recognition and binding to CArG box motifs. FRUITFULL1 (FUL1) is a shared putative target of STM3 and J2 and these TFs antagonistically regulate FUL1 in inflorescence branching. Moreover, STM3 physically interacts with J2 to mediate its cytosolic redistribution and restricts J2 repressor activity by reducing its binding to target genes. Conversely, J2 limits STM3 regulation of target genes by transcriptional repression of the STM3 promoter and reducing STM3-binding activity. Our study thus reveals an antagonistic regulatory relationship in which STM3 and J2 control tomato IM determinacy and branch number.

Malus Species with Diverse Bloom Times Exhibit Variable Rates of Floral Development

In response to challenges caused by climate change, apple (Malus ×domestica) breeding programs must quickly develop more resilient cultivars. One strategy is to breed for various bloom times. Members of the genus Malus, including domesticated apple, wild species, and hybrids, exhibit striking variations in the bloom date. Although bloom time is strongly influenced by chilling requirements, other aspects of floral development in Malus and their contributions to bloom time are less known. The purpose of this study was to investigate potential connections between predormancy flower development and final bloom time in Malus species. We performed a phenological analysis of flower development in wild and domesticated apple with extreme differences in bloom time over the course of one developmental season. We tracked histological changes in the floral apex of representatives of three early-blooming Malus genotypes (M. ×domestica ‘Anna’ PI 280400, M. orthocarpa PI 589392, M. sylvestris PI 633824) and three late-blooming genotypes (M. angustifolia PI 589763, M. angustifolia PI 613880, M. ×domestica ‘Koningszuur’ PI 188517). Our study documented their floral meristem progression and organ development and expanded on current staging systems for apple flower development to describe the changes observed. The developmental trajectories of each genotype did not group according to bloom category, and we observed variations in the floral development stage at the time of dormancy onset.

Tomato APETALA2 family member SlTOE1 regulates inflorescence branching by repressing SISTER OF TM3.

Inflorescence architecture directly impacts yield potential in most crops. As a model of sympodial plants, tomato (Solanum lycopersicum) inflorescence exhibits highly structural plasticity. However, the genetic regulatory network of inflorescence architecture in tomato remains unclear. Here, we investigated a modulator of inflorescence branching in tomato, TARGET OF EAT1 (SlTOE1), an APETALA2 (AP2) family member found to be predominantly expressed in the floral meristem (FM) of tomato. sltoe1 knockout mutants displayed highly branched inflorescences and defective floral organs. Transcriptome analysis revealed that SISTER OF TM3 (STM3) and certain floral development-related genes were upregulated in the flower meristem of sltoe1. SlTOE1 could directly bind the promoters of STM3 and Tomato MADS-box gene 3 (TM3) to repress their transcription. Simultaneous mutation of STM3 and TM3 partially restored the inflorescence branching of the sltoe1cr mutants, suggesting that SlTOE1 regulates inflorescence development, at least in part through an SlTOE1STM3/TM3 module. Genetic analysis showed that SlTOE1 and ENHANCER OF JOINTLESS 2 (EJ2) additively regulate tomato inflorescence branching; their double mutants showed more extensive inflorescence branching. Our findings uncover a pathway controlling tomato inflorescence branching and offer deeper insight into the functions of AP2 subfamily members.

Floral development of one of the oldest dioecious lineages of Arecaceae reveals different stages of dicliny in pistillate and staminate flowers

AbstractArecaceae subtribe Mauritiinae are a lineage of Neotropical dioecious species in subfamily Calamoideae, the earliest diverging and most diverse group of palms regarding sexual systems. Ontogenetic and anatomical studies of reproductive structures contribute to the understanding of evolutionary relationships, but there is a lack of detailed information. We describe the anatomical floral development of Lepidocaryum tenue, Mauritia flexuosa and Mauritiella armata (subtribe Mauritiinae) using standard light microscopy techniques. Three central moments in the development of pistillate and staminate flowers were identified: the initial phase of development of the floral meristem; the phase of determination of the whorls that will compose the pistillate and staminate flowers; and the phase of differentiation (pre-anthesis) of these whorls. Although the pre-anthetic flowers are diclinous, they are initially monoclinous, suggesting a hermaphrodite ancestor for Mauritiinae. The development is asynchronous since, in pre-anthesis, the pistillate flowers have staminodes that produce non-viable pollen grains, whereas the staminate flowers do not even have a pistillode. Staminodes may have a secondary function in attracting floral visitors.

Cold stress induces malformed tomato fruits by breaking the feedback loops of stem cell regulation in floral meristem.

Fruit malformation is a major constrain in fruit production worldwide resulting in substantial economic losses. The farmers for decades noticed that the chilling temperature before blooming often caused malformed fruits. However, the molecular mechanism underlying this phenomenon is unclear. Here we examined the fruit development in response to cold stress in tomato, and demonstrated that short-term cold stress increased the callose accumulation in both shoot apical and floral meristems, resulting in the symplastic isolation and altered intercellular movement of WUS. In contrast to the rapidly restored SlWUS transcription during the recovery from cold stress, the callose removal was delayed due to obstructed plasmodesmata. The delayed reinstatement of cell-to-cell transport of SlWUS prevented the activation of SlCLV3 and TAG1, causing the interrupted feedback inhibition of SlWUS expression, leading to the expanded stem cell population and malformed fruits. We further showed that the callose dynamics in response to short-term cold stress presumably exploits the mechanism of bud dormancy during the seasonal growth, involving two antagonistic hormones, abscisic acid and gibberellin. Our results provide a novel insight into the cold stress regulated malformation of fruit.

All's well that ends well: the timing of floral meristem termination.

Floral meristem termination (FMT) represents one of the defining features of a floral meristem relative to a vegetative meristem. Timing of FMT is a major determinant of the total number of organs in a flower, and canalization toward relatively rapid FMT is considered to have been a major force in shaping angiosperm evolution. For decades, investigation of FMT has been focused on model systems that only produce four whorls of organs in a flower, while little is known about the molecular basis that underlies nature variation in the timing of FMT. Here, we hypothesize on how known pathways could have been modified to generate variation in FMT and explain how developing new model systems will help to deepen our understanding of the genetic control and evolution of FMT.