AINTEGUMENTA-like (AIL) genes are expressed in young tissues and may specify meristematic or division-competent states

Plant regeneration in the new era: from molecular mechanisms to biotechnology applications

Plants or tissues can be regenerated through various pathways. Like animal regeneration, cell totipotency and pluripotency are the molecular basis of plant regeneration. Detailed systematic studies on Arabidopsis thaliana gradually unravel the fundamental mechanisms and principles underlying plant regeneration. Specifically, plant hormones, cell division, epigenetic remodeling, and transcription factors play crucial roles in reprogramming somatic cells and reestablishing meristematic cells. Recent research on basal non-vascular plants and monocot crops has revealed that plant regeneration differs among species, with various plant species using distinct mechanisms and displaying significant differences in regenerative capacity. Conducting multi-omics studies at the single-cell level, tracking plant regeneration processes in real-time, and deciphering the natural variation in regenerative capacity will ultimately help understand the essence of plant regeneration, improve crop regeneration efficiency, and contribute to future crop design.

Application of Developmental Regulators for Enhancing Plant Regeneration and Genetic Transformation

Establishing plant regeneration systems and efficient genetic transformation techniques plays a crucial role in plant functional genomics research and the development of new crop varieties. The inefficient methods of transformation and regeneration of recalcitrant species and the genetic dependence of the transformation process remain major obstacles. With the advancement of plant meristematic tissues and somatic embryogenesis research, several key regulatory genes, collectively known as developmental regulators, have been identified. In the field of plant genetic transformation, the application of developmental regulators has recently garnered significant interest. These regulators play important roles in plant growth and development, and when applied in plant genetic transformation, they can effectively enhance the induction and regeneration capabilities of plant meristematic tissues, thus providing important opportunities for improving genetic transformation efficiency. This review focuses on the introduction of several commonly used developmental regulators. By gaining an in-depth understanding of and applying these developmental regulators, it is possible to further enhance the efficiency and success rate of plant genetic transformation, providing strong support for plant breeding and genetic engineering research.

Comprehensive deciphering the alternative splicing patterns involved in leaf morphogenesis of Liriodendron chinense

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

The roles of epigenetic regulators in plant regeneration: Exploring patterns amidst complex conditions

Plants possess remarkable capability to regenerate upon tissue damage or optimal environmental stimuli. This ability not only serves as a crucial strategy for immobile plants to survive through harsh environments, but also made numerous modern plant improvements techniques possible. At the cellular level, this biological process involves dynamic changes in gene expression that redirect cell fate transitions. It is increasingly recognized that chromatin epigenetic modifications, both activating and repressive, intricately interact to regulate this process. Moreover, the outcomes of epigenetic regulation on regeneration are influenced by factors such as the differences in regenerative plant species and donor tissue types, as well as the concentration and timing of hormone treatments. In this review, we focus on several well-characterized epigenetic modifications and their regulatory roles in the expression of widely studied morphogenic regulators, aiming to enhance our understanding of the mechanisms by which epigenetic modifications govern plant regeneration.

Large-scale single-cell profiling of stem cells uncovers redundant regulators of shoot development and yield trait variation

Stem cells in plant shoots are a rare population of cells that produce leaves, fruits and seeds, vital sources for food and bioethanol. Uncovering regulators expressed in these stem cells will inform crop engineering to boost productivity. Single-cell analysis is a powerful tool for identifying regulators expressed in specific groups of cells. However, accessing plant shoot stem cells is challenging. Recent single-cell analyses of plant shoots have not captured these cells, and failed to detect stem cell regulators like CLAVATA3 and WUSCHEL . In this study, we finely dissected stem cell-enriched shoot tissues from both maize and arabidopsis for single-cell RNA-seq profiling. We optimized protocols to efficiently recover thousands of CLAVATA3 and WUSCHEL expressed cells. A cross-species comparison identified conserved stem cell regulators between maize and arabidopsis. We also performed single-cell RNA-seq on maize stem cell overproliferation mutants to find additional candidate regulators. Expression of candidate stem cell genes was validated using spatial transcriptomics, and we functionally confirmed roles in shoot development. These candidates include a family of ribosome-associated RNA-binding proteins, and two families of sugar kinase genes related to hypoxia signaling and cytokinin hormone homeostasis. These large-scale single-cell profiling of stem cells provide a resource for mining stem cell regulators, which show significant association with yield traits. Overall, our discoveries advance the understanding of shoot development and open avenues for manipulating diverse crops to enhance food and energy security.

Unlocking dynamic root phenotypes for simultaneous enhancement of water and phosphorus uptake

Phosphorus (P) and water are crucial for plant growth, but their availability is challenged by climate change, leading to reduced crop production and global food security. In many agricultural soils, crop productivity is confronted by both water and P limitations. The diminished soil moisture decreases available P due to reduced P diffusion, and inadequate P availability diminishes tissue water status through modifications in stomatal conductance and a decrease in root hydraulic conductance. P and water display contrasting distributions in the soil, with P being concentrated in the topsoil and water in the subsoil. Plants adapt to water- and P-limited environments by efficiently exploring localized resource hotspots of P and water through the adaptation of their root system. Thus, developing cultivars with improved root architecture is crucial for accessing and utilizing P and water from arid and P-deficient soils. To meet this goal, breeding towards multiple advantageous root traits can lead to better cultivars for water- and P-limited environments. This review discusses the interplay of P and water availability and highlights specific root traits that enhance the exploration and exploitation of optimal resource-rich soil strata while reducing metabolic costs. We propose root ideotype models, including 'topsoil foraging', 'subsoil foraging', and 'topsoil/subsoil foraging' for maize (monocot) and common bean (dicot). These models integrate beneficial root traits and guide the development of water- and P-efficient cultivars for challenging environments.

Regulation of regeneration in Arabidopsis thaliana

We employed several algorithms with high efficacy to analyze the public transcriptomic data, aiming to identify key transcription factors (TFs) that regulate regeneration in Arabidopsis thaliana. Initially, we utilized CollaborativeNet, also known as TF-Cluster, to construct a collaborative network of all TFs, which was subsequently decomposed into many subnetworks using the Triple-Link and Compound Spring Embedder (CoSE) algorithms. Functional analysis of these subnetworks led to the identification of nine subnetworks closely associated with regeneration. We further applied principal component analysis and gene ontology (GO) enrichment analysis to reduce the subnetworks from nine to three, namely subnetworks 1, 12, and 17. Searching for TF-binding sites in the promoters of the co-expressed and co-regulated (CCGs) genes of all TFs in these three subnetworks and Triple-Gene Mutual Interaction analysis of TFs in these three subnetworks with the CCGs involved in regeneration enabled us to rank the TFs in each subnetwork. Finally, six potential candidate TFs-WOX9A, LEC2, PGA37, WIP5, PEI1, and AIL1 from subnetwork 1-were identified, and their roles in somatic embryogenesis (GO:0010262) and regeneration (GO:0031099) were discussed, so were the TFs in Subnetwork 12 and 17 associated with regeneration. The TFs identified were also assessed using the CIS-BP database and Expression Atlas. Our analyses suggest some novel TFs that may have regulatory roles in regeneration and embryogenesis and provide valuable data and insights into the regulatory mechanisms related to regeneration. The tools and the procedures used here are instrumental for analyzing high-throughput transcriptomic data and advancing our understanding of the regulation of various biological processes of interest.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-023-00121-9.

MdAIL5 overexpression promotes apple adventitious shoot regeneration by regulating hormone signaling and activating the expression of shoot development-related genes

Adventitious shoot (AS) regeneration is a significant factor in the genetic transformation of horticultural plants. It is also a noteworthy approach to their vegetative propagation. AS regeneration remains highly dependent on the genotype or maturity of explants. We here found that the AS regeneration abilities of apple leaves were positively correlated with MdAIL5 expression. MdAIL5 overexpression dramatically increased AS regeneration efficiency. Notably, MdAIL5 overexpression could restore the AS formation ability of explants to a certain extent, which was lost with an increase in maturity. Endogenous hormone detection revealed that MdAIL5 overexpression changed the contents of auxin, cytokinin (CK), and other hormones in apple leaves. Transcriptome analysis revealed that many genes related to auxin, CK, and brassinolide signaling pathways were significantly and differentially expressed between MdAIL5-overexpressing transgenic apple and wild-type apple plants. Yeast one-hybrid assays, the electrophoretic mobility shift assay, and the dual-luciferase reporter assay revealed that MdAIL5 directly binds to MdARF9 and MdHB14 promoters and positively affects their expression. We here established a model of MdAIL5 regulating AS formation, which acts as a theoretical basis for facilitating genotype- or explant maturity-independent AS regeneration in the future.

Differences in both expression and protein activity contribute to the distinct functions of AINTEGUMENTA compared with AINTEGUMENTA-LIKE 5 and AINTEGUMENTA-LIKE 7

Three members of the Arabidopsis AINTEGUMENTA-LIKE/PLETHORA (AIL/PLT) transcription factor family, AIL5/PLT5, AIL6/PLT3, and AIL7/PLT7, exhibit partially overlapping roles with AINTEGUMENTA (ANT) during flower development. Loss of ANT function alone results in smaller floral organs and female sterility indicating that some ANT functions cannot be provided by these related transcription factors. Previously, we showed that expression of AIL6 at the same levels and spatial pattern as ANT could largely rescue the defects of ant mutants. This suggested that the functional differences between ANT and AIL6 were primarily a consequence of expression differences. Here, we investigated the functional differences between ANT and both AIL5 and AIL7 by expressing these two AILs under the control of the ANT promoter. We found that only ANT:gAIL5 lines with much higher amounts of AIL5 mRNA as compared with ANT could compensate for loss of ANT function. ANT:gAIL7 lines with AIL7 mRNA levels similar to those of ANT were able to rescue some but not all aspects of the ant mutant phenotype. Thus, expression differences alone cannot explain the functional differences between ANT and these two related proteins. Studies in yeast show that AIL5 and AIL7 have lower transcriptional activation activities as compared with ANT and AIL6 when bound to the consensus ANT DNA binding site. Our results suggest that differences in both expression and protein activity contribute to the functional specificity of ANT compared with AIL5 and AIL7.

FUSCA3-induced AINTEGUMENTA-like 6 manages seed dormancy and lipid metabolism

FUSCA 3 (FUS3), a seed master regulator, plays critical role in seed dormancy and oil accumulation. However, its downstream regulation mechanisms remain poorly understood. Here, we explored the roles of AINTEGUMENTA-like 6 (AIL6), a seed transcription factor, in these processes. The activation of AIL6 by FUS3 was demonstrated by dual-LUC assay. Seeds of ail6 mutants showed alterations in fatty acid compositions, and both AtAIL6 (AIL6 from Arabidopsis thaliana) and BnaAIL6 (AIL6 from Brassica napus) rescued the phenotype. Over-expression (OE) of AIL6s reversed changes in seed fatty acid composition. Notably, OE lines showed low seed germination rates down to 12% compared to 100% of wild-type Col-0. Transcriptome analysis of the mutant and an OE line indicated widespread expression changes of genes involved in lipid metabolism and phytohormone pathways. In OE mature seeds, GA4 content decreased more than 15-fold, while abscisic acid and indole-3-acetic acid (IAA) contents clearly increased. Exogenous GA3 treatments did not effectively rescue the low germination rate. Nicking seed coats increased germination rates from 25% to nearly 80% while the wild-type rdr6-11 is 100% and 98% respectively, and elongation of storage time also improved seed germination. Furthermore, dormancy imposed by AIL6 was fully released in the della quintuple mutant. Together, our results indicate AIL6 acts as a manager downstream of FUS3 in seed dormancy and lipid metabolism.

The MIO1-MtKIX8 module regulates the organ size in Medicago truncatula

Plant organ size is an important agronomic trait tightly related to crop yield. However, the molecular mechanisms underlying organ size regulation remain largely unexplored in legumes. We previously characterized a key regulator F-box protein MINI ORGAN1 (MIO1)/SMALL LEAF AND BUSHY1 (SLB1), which controls plant organ size in the model legume Medicago truncatula. In order to further dissect the molecular mechanism, MIO1 was used as the bait to screen its interacting proteins from a yeast library. Subsequently, a KIX protein, designated MtKIX8, was identified from the candidate list. The interaction between MIO1 and MtKIX8 was confirmed further by Y2H, BiFC, split-luciferase complementation and pull-down assays. Phylogenetic analyses indicated that MtKIX8 is highly homologous to Arabidopsis KIX8, which negatively regulates organ size. Moreover, loss-of-function of MtKIX8 led to enlarged leaves and seeds, while ectopic expression of MtKIX8 in Arabidopsis resulted in decreased cotyledon area and seed weight. Quantitative reverse-transcription PCR and in situ hybridization showed that MtKIX8 is expressed in most developing organs. We also found that MtKIX8 serves as a crucial molecular adaptor, facilitating interactions with BIG SEEDS1 (BS1) and MtTOPLESS (MtTPL) proteins in M. truncatula. Overall, our results suggest that the MIO1-MtKIX8 module plays a significant and conserved role in the regulation of plant organ size. This module could be a good target for molecular breeding in legume crops and forages.

Genome-wide identification of Apetala2 gene family in Hypericum perforatum L and expression profiles in response to different abiotic and hormonal treatments

The Apetala2 (AP2) gene family of transcription factors (TFs) play important functions in plant development, hormonal response, and abiotic stress. To reveal the biological functions and the expression profiles of AP2 genes in Hypericum perforatum, genome-wide identification of HpAP2 family members was conducted.

Methods

We identified 21 AP2 TFs in H. perforatum using bioinformatic methods; their physical and chemical properties, gene structures, conserved motifs, evolutionary relationships, cis-acting elements, and expression patterns were investigated.

Results

We found that based on the structural characteristics and evolutionary relationships, the HpAP2 gene family can be divided into three subclasses: euANT, baselANT, and euAP2. A canonical HpAP2 TF shared a conserved protein structure, while a unique motif 6 was found in HpAP2_1, HpAP2_4, and HpAP2_5 from the euANT subgroup, indicating potential biological and regulatory functions of these genes. Furthermore, a total of 59 cis-acting elements were identified, most of which were associated with growth, development, and resistance to stress in plants. Transcriptomics data showed that 57.14% of the genes in the AP2 family were differentially expressed in four organs. For example, HpAP2_18 was specifically expressed in roots and stems, whereas HpAP2_17 and HpAP2_11 were specifically expressed in leaves and flowers, respectively. HpAP2_5, HpAP2_11, and HpAP2_18 showed tissue-specific expression patterns and responded positively to hormones and abiotic stresses.

Conclusion

These results demonstrated that the HpAP2 family genes are involved in diverse developmental processes and generate responses to abiotic stress conditions in H. perforatum. This article, for the first time, reports the identification and expression profiles of the AP2 family genes in H. perforatum, laying the foundation for future functional studies with these genes.

The evolutionary patterns, expression profiles, and genetic diversity of expanded genes in barley

Gene duplication resulting from whole-genome duplication (WGD), small-scale duplication (SSD), or unequal hybridization plays an important role in the expansion of gene families. Gene family expansion can also mediate species formation and adaptive evolution. Barley (Hordeum vulgare) is the world's fourth largest cereal crop, and it contains valuable genetic resources due to its ability to tolerate various types of environmental stress. In this study, 27,438 orthogroups in the genomes of seven Poaceae were identified, and 214 of them were significantly expanded in barley. The evolutionary rates, gene properties, expression profiles, and nucleotide diversity between expanded and non-expanded genes were compared. Expanded genes evolved more rapidly and experienced lower negative selection. Expanded genes, including their exons and introns, were shorter, they had fewer exons, their GC content was lower, and their first exons were longer compared with non-expanded genes. Codon usage bias was also lower for expanded genes than for non-expanded genes; the expression levels of expanded genes were lower than those of non-expanded genes, and the expression of expanded genes showed higher tissue specificity than that of non-expanded genes. Several stress-response-related genes/gene families were identified, and these genes could be used to breed barley plants with greater resistance to environmental stress. Overall, our analysis revealed evolutionary, structural, and functional differences between expanded and non-expanded genes in barley. Additional studies are needed to clarify the functions of the candidate genes identified in our study and evaluate their utility for breeding barley plants with greater stress resistance.

Genome-wide characterization of AINTEGUMENTA-LIKE family in Medicago truncatula reveals the significant roles of AINTEGUMENTAs in leaf growth

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

Ovule initiation: the essential step controlling offspring number in Arabidopsis

Seed is the offspring of angiosperms. Plants produce large numbers of seeds to ensure effective reproduction and survival in varying environments. Ovule is a fundamentally important organ and is the precursor of the seed. In Arabidopsis and other plants characterized by multi-ovulate ovaries, ovule initiation determines the maximal ovule number, thus greatly affecting seed number per fruit and seed yield. Investigating the regulatory mechanism of ovule initiation has both scientific and economic significance. However, the genetic and molecular basis underlying ovule initiation remains unclear due to technological limitations. Very recently, rules governing the multiple ovules initiation from one placenta have been identified, the individual functions and crosstalk of phytohormones in regulating ovule initiation have been further characterized, and new regulators of ovule boundary are reported, therefore expanding the understanding of this field. In this review, we present an overview of current knowledge in ovule initiation and summarize the significance of ovule initiation in regulating the number of plant offspring, as well as raise insights for the future study in this field that provide potential routes for the improvement of crop yield.

My favorite flowering image: 'giant' Arabidopsis flowers

A fascinating aspect of floral diversity is the dramatic difference in flower size observed in nature. The largest flowers in the world, Rafflesia arnoldii, span several feet while flowers of the genus Wolffia are microscopic. My own particular interest in flower size started when I overexpressed the Arabidopsis gene AINTEGUMENTA (ANT) and observed a larger flower phenotype.

Regulatory Networks of Flowering Genes in Angelica sinensis during Vernalization

Angelica sinensis is a low-temperature and long-day perennial herb that has been widely used for cardio-cerebrovascular diseases in recent years. In commercial cultivation, up to 40% of flowering decreases the officinal yield of roots and accumulation of bioactive compounds. Although the regulatory mechanism of flowering genes during the photoperiod has been revealed, the networks during vernalization have not been mapped. Here, transcriptomics profiles of A. sinensis with uncompleted (T1), completed (T2) and avoided vernalization (T3) were performed using RNA-seq, and genes expression was validated with qRT-PCR. A total of 61,241 isoforms were annotated on KEGG, KOG, Nr and Swiss-Prot databases; 4212 and 5301 differentially expressed genes (DEGs) were observed; and 151 and 155 genes involved in flowering were dug out at T2 vs. T1 and T3 vs. T1, respectively. According to functional annotation, 104 co-expressed genes were classified into six categories: FLC expression (22; e.g., VILs, FCA and FLK), sucrose metabolism (12; e.g., TPSs, SUS3 and SPSs), hormone response (18; e.g., GID1B, RAP2s and IAAs), circadian clock (2; i.e., ELF3 and COR27), downstream floral integrators and meristem identity (15; e.g., SOC1, AGL65 and SPLs) and cold response (35; e.g., PYLs, ERFs and CORs). The expression levels of candidate genes were almost consistent with FPKM values and changes in sugar and hormone contents. Based on their functions, four pathways that regulate flowering during vernalization were mapped, including the vernalization pathway, the autonomic pathway, the age pathway and the GA (hormone) pathway. This transcriptomic analysis provides new insights into the gene-regulatory networks of flowering in A. sinensis.

Impact of phosphorous-deficit conditions on morpho-physiological traits and phosphorous metabolism in chickpea genotypes

Chickpea, an important food legume, is primarily grown on marginal soils with low soil fertility. Although chickpea can fix N, soil phosphorus (P) deficiency in crop growing areas is a major limiting factor for chickpea production. This study was undertaken to evaluate twenty-five chickpea cultivars for morpho-physiological traits and yield under low and normal phosphorous conditions. Based on morpho-physiological traits such as length and area of roots and shoots, root length density, root and shoot biomass, chlorophyll content, number of nodules and root tips, tolerance indices and yield, these cultivars were characterised into susceptible (ICC67, ICC1915, ICC2593, ICC5337, ICC5879, ICC8950, ICC13441, ICC1483, ICC15606 and ICC15888), tolerant (ICC10755, IG72070, ICCV97105, ICCV2, ICCV92809, ICCV92337 and ICCV95423) and the remaining cultivars were moderately tolerant to phosphorous-deficit conditions. Higher activities of enzymes of phosphorous metabolism such as acid phosphatase and phytase in roots and nodules of tolerant chickpea cultivars (ICCV97105, ICCV92337, ICCV95423) as compared to susceptible cultivars (ICC67, ICC15606, ICC15888) at different developmental stages might be attributing to their better performance for growth parameters and productivity traits under phosphorous-deficit conditions.

Transcription Factor RrANT1 of Rosa rugosa Positively Regulates Flower Organ Size in Petunia hybrida

The flower is the main organ that produces essential oils in many plants. The yield of raw flowers and the number of secretory epidermal cells are the main factors for essential oil production. The cultivated rose species “Pingyin 1” in China was used to study the effect of RrANT1 on floral organ development. Eighteen AP2 transcription factors with dual AP2 domains were identified from Rosa rugosa genome. RrANT1 belonged to euANT. The subcellular localization results showed that RrANT1 protein is localized in the nucleus. The relative expression level of RrANT1 in the receptacle is higher than that in petals in the developmental stages, and both decreased from the initial phase to senescence. Compared with the RrANT1 expression level in petals in the blooming stage, RrANT1 expression level was significant in petals (~48.8) and highest in the receptacle (~102.5) in the large bud stage. It was only highly expressed in the receptacle (~39.4) in the blooming period. RrANT1 overexpression significantly increased petunia flower and leaf sizes (~1.2), as well as flower fresh weight (~30%). The total number of epidermis cells in the petals of overexpressing plants significantly increased (>40%). This study concluded that RrANT1 overexpression can increase the size and weight of flowers by promoting cell proliferation, providing a basis for creating new rose germplasm to increase rose and essential oil yield.

Transcriptome analysis of transgenic apple fruit overexpressing microRNA172 reveals candidate transcription factors regulating apple fruit development at early stages

Background

MicroRNA172 (miR172) has been proven to be critical for fruit growth, since elevated miR172 activity blocks the growth of apple (Malus x domestica Borkh.) fruit. However, it is not clear how overexpression of miR172 affects apple fruit developmental processes.

Methods

To answer this question, the present study, analyzed global transcriptional changes in miR172-overexpressing (miR172OX) and nongenetically modified wild-type (WT) apple fruit at two developmental stages and in different fruit tissues via RNA-seq. In addition, two cultivars, ‘Hanfu’ and ‘M9’, which have naturally fruit size variation, were included to identify miR172-dependent DEGs. qRT–PCRwas used to verify the reliability of our RNA-seq data.

Results

Overexpression of miR172 altered the expression levels of many cell proliferation- and cell expansion-related genes. Twenty-four libraries were generated, and 10,338 differentially expressed genes (DEGs) were detected between miR172OX and WT fruit tissues. ‘Hanfu’ and ‘M9’ are two common cultivars that bear fruit of different sizes (250 g and 75 g, respectively). Six libraries were generated, and 3,627 DEGs were detected between ‘Hanfu’ and ‘M9’. After merging the two datasets, 6,888 candidate miR172-specific DEGs were identified. The potential networks associated with fruit size triggered traits were defined among genes belonging to the families of hormone synthesis, signaling pathways, and transcription factors. Our comparative transcriptome analysis provides insights into transcriptome responses to miR172 overexpression in apple fruit and a valuable database for future studies to validate functional genes and elucidate the fruit developmental mechanisms in apple.

Identification and Analysis of the AP2 Subfamily Transcription Factors in the Pecan (Carya illinoinensis)

The AP2 transcriptional factors (TFs) belong to the APETALA2/ ethylene-responsive factor (AP2/ERF) superfamily and regulate various biological processes of plant growth and development, as well as response to biotic and abiotic stresses. However, genome-wide research on the AP2 subfamily TFs in the pecan (Carya illinoinensis) is rarely reported. In this paper, we identify 30 AP2 subfamily genes from pecans through a genome-wide search, and they were unevenly distributed on the pecan chromosomes. Then, a phylogenetic tree, gene structure and conserved motifs were further analyzed. The 30 AP2 genes were divided into euAP2, euANT and basalANT three clades. Moreover, the cis-acting elements analysis showed many light responsive elements, plant hormone-responsive elements and abiotic stress responsive elements are found in CiAP2 promoters. Furthermore, a qPCR analysis showed that genes clustered together usually shared similar expression patterns in euAP2 and basalANT clades, while the expression pattern in the euANT clade varied greatly. In developing pecan fruits, CiAP2-5, CiANT1 and CiANT2 shared similar expression patterns, and their expression levels decreased with fruit development. CiANT5 displayed the highest expression levels in developing fruits. The subcellular localization and transcriptional activation activity assay demonstrated that CiANT5 is located in the nucleus and functions as a transcription factor with transcriptional activation activity. These results help to comprehensively understand the pecan AP2 subfamily TFs and lay the foundation for further functional research on pecan AP2 family genes.

Genome-wide survey and identification of AP2/ERF genes involved in shoot and leaf development in Liriodendron chinense

BACKGROUND

Liriodendron chinense is a distinctive ornamental tree species due to its unique leaves and tulip-like flowers. The discovery of genes involved in leaf development and morphogenesis is critical for uncovering the underlying genetic basis of these traits. Genes in the AP2/ERF family are recognized as plant-specific transcription factors that contribute to plant growth, hormone-induced development, ethylene response factors, and stress responses.

RESULTS

In this study, we identified 104 putative AP2/ERF genes in the recently released L. chinense genome and transcriptome database. In addition, all 104 genes were grouped into four subfamilies, the AP2, ERF, RAV, and Soloist subfamilies. This classification was further supported by the results of gene structure and conserved motif analyses. Intriguingly, after application of a series test of cluster analysis, three AP2 genes, LcERF 94, LcERF 96, and LcERF 98, were identified as tissue-specific in buds based on the expression profiles of various tissues. These results were further validated via RT-qPCR assays and were highly consistent with the STC analysis. We further investigated the dynamic changes of immature leaves by dissecting fresh shoots into seven discontinuous periods, which were empirically identified as shoot apical meristem (SAM), leaf primordia and tender leaf developmental stages according to the anatomic structure. Subsequently, these three candidates were highly expressed in SAM and leaf primordia but rarely in tender leaves, indicating that they were mainly involved in early leaf development and morphogenesis. Moreover, these three genes displayed nuclear subcellular localizations through the transient transformation of tobacco epidermal cells.

CONCLUSIONS

Overall, we identified 104 AP2/ERF family members at the genome-wide level and discerned three candidate genes that might participate in the development and morphogenesis of the leaf primordium in L. chinense.

An apple (Malus domestica) AP2/ERF transcription factor modulates carotenoid accumulation

Color is an important trait for horticultural crops. Carotenoids are one of the main pigments for coloration and have important implications for photosynthesis in plants and benefits for human health. Here, we identified an APETALA2 (AP2)/ETHYLENE RESPONSE FACTOR (ERF) transcription factor named MdAP2-34 in apple (Malus domestica Borkh.). MdAP2-34 expression exhibited a close correlation with carotenoid content in 'Benin Shogun' and 'Yanfu 3' fruit flesh. MdAP2-34 promotes carotenoid accumulation in MdAP2-34-OVX transgenic apple calli and fruits by participating in the carotenoid biosynthesis pathway. The major carotenoid contents of phytoene and β-carotene were much higher in overexpressing MdAP2-34 transgenic calli and fruit skin, yet the predominant compound of lutein showed no obvious difference, indicating that MdAP2-34 regulates phytoene and β-carotene accumulation but not lutein. MdPSY2-1 (phytoene synthase 2) is a major gene in the carotenoid biosynthesis pathway in apple fruit, and the MdPSY2-1 gene is directly bound and transcriptionally activated by MdAP2-34. In addition, overexpressing MdPSY2-1 in apple calli mainly increases phytoene and total carotenoid contents. Our findings will advance and extend our understanding of the complex molecular mechanisms of carotenoid biosynthesis in apple, and this research is valuable for accelerating the apple breeding process.

Interkingdom Comparison of Threonine Metabolism for Stem Cell Maintenance in Plants and Animals

In multicellular organisms, tissue generation, maintenance, and homeostasis depend on stem cells. Cellular metabolic status is an essential component of different differentiated states, from stem to fully differentiated cells. Threonine (Thr) metabolism has emerged as a critical factor required to maintain pluripotent/multipotent stem cells in both plants and animals. Thus, both kingdoms conserved or converged upon this fundamental feature of stem cell function. Here, we examine similarities and differences in Thr metabolism-dependent mechanisms supporting stem cell maintenance in these two kingdoms. We then consider common features of Thr metabolism in stem cell maintenance and predict and speculate that some knowledge about Thr metabolism and its role in stem cell function in one kingdom may apply to the other. Finally, we outline future research directions to explore these hypotheses.

The effect of AINTEGUMENTA-LIKE 7 over-expression on seed fatty acid biosynthesis, storage oil accumulation and the transcriptome in Arabidopsis thaliana

AIL7 over-expression modulates fatty acid biosynthesis and triacylglycerol accumulation in Arabidopsis developing seeds through the transcriptional regulation of associated genes. Seed fatty acids (FAs) and triacylglycerol (TAG) contribute to many functions in plants, and seed lipids have broad food, feed and industrial applications. As a result, an enormous amount of attention has been dedicated towards uncovering the regulatory cascade responsible for the fine-tuning of the lipid biosynthetic pathway in seeds, which is regulated in part through the action of LEAFY COTYLEDON1, ABSCISSIC ACID INSENSITIVE 3, FUSCA3 and LEC2 (LAFL) transcription factors. Although AINTEGUMENTA-LIKE 7 (AIL7) is involved in meristematic function and shoot phyllotaxy, its effect in the context of lipid biosynthesis has yet to be assessed. Here, we generated AIL7 seed-specific over-expression lines and found that they exhibited significant alterations in FA composition and decreased total lipid accumulation in seeds. Seeds and seedlings from transgenic lines also exhibited morphological deviations compared to wild type. Correspondingly, RNA-Seq analysis demonstrated that the expression of many genes related to FA biosynthesis and TAG breakdown were significantly altered in developing siliques from transgenic lines compared to wild-type plants. The seed-specific over-expression of AIL7 also altered the expression profiles of many genes related to starch metabolism, photosynthesis and stress response, suggesting further roles for AIL7 in plants. These findings not only advance our understanding of the lipid biosynthetic pathway in seeds, but also provide evidence for additional functions of AIL7, which could prove valuable in downstream breeding and/or metabolic engineering endeavors.

A multiscale analysis of early flower development in Arabidopsis provides an integrated view of molecular regulation and growth control

We have analyzed the link between the gene regulation and growth during the early stages of flower development in Arabidopsis. Starting from time-lapse images, we generated a 4D atlas of early flower development, including cell lineage, cellular growth rates, and the expression patterns of regulatory genes. This information was introduced in MorphoNet, a web-based platform. Using computational models, we found that the literature-based molecular network only explained a minority of the gene expression patterns. This was substantially improved by adding regulatory hypotheses for individual genes. Correlating growth with the combinatorial expression of multiple regulators led to a set of hypotheses for the action of individual genes in morphogenesis. This identified the central factor LEAFY as a potential regulator of heterogeneous growth, which was supported by quantifying growth patterns in a leafy mutant. By providing an integrated view, this atlas should represent a fundamental step toward mechanistic models of flower development.

The Evolution of euAPETALA2 Genes in Vascular Plants: From Plesiomorphic Roles in Sporangia to Acquired Functions in Ovules and Fruits

The field of evolutionary developmental biology can help address how morphological novelties evolve, a key question in evolutionary biology. In Arabidopsis thaliana, APETALA2 (AP2) plays a role in the development of key plant innovations including seeds, flowers, and fruits. AP2 belongs to the AP2/ETHYLENE RESPONSIVE ELEMENT BINDING FACTOR family which has members in all viridiplantae, making it one of the oldest and most diverse gene lineages. One key subclade, present across vascular plants is the euAPETALA2 (euAP2) clade, whose founding member is AP2. We reconstructed the evolution of the euAP2 gene lineage in vascular plants to better understand its impact on the morphological evolution of plants, identifying seven major duplication events. We also performed spatiotemporal expression analyses of euAP2/TOE3 genes focusing on less explored vascular plant lineages, including ferns, gymnosperms, early diverging angiosperms and early diverging eudicots. Altogether, our data suggest that euAP2 genes originally contributed to spore and sporangium development, and were subsequently recruited to ovule, fruit and floral organ development. Finally, euAP2 protein sequences are highly conserved; therefore, changes in the role of euAP2 homologs during development are most likely due to changes in regulatory regions.

AINTEGUMENTA and AINTEGUMENTA-LIKE6 directly regulate floral homeotic, growth, and vascular development genes in young Arabidopsis flowers

Arabidopsis flower primordia give rise to organ primordia in stereotypical positions within four concentric whorls. Floral organ primordia in each whorl undergo distinct developmental programs to become one of four organ types (sepals, petals, stamens, and carpels). The Arabidopsis transcription factors AINTEGUMENTA (ANT) and AINTEGUMENTA-LIKE6 (AIL6) are required for correct positioning of floral organ initiation, contribute to the specification of floral organ identity, and regulate the growth and morphogenesis of developing floral organs. To gain insight into the molecular mechanisms by which ANT and AIL6 contribute to floral organogenesis, we identified the genome-wide binding sites of both ANT and AIL6 in stage 3 flower primordia, the developmental stage at which sepal primordia become visible and class B and C floral homeotic genes are first expressed. AIL6 binds to a subset of ANT sites, suggesting that AIL6 regulates some but not all of the same target genes as ANT. ANT- and AIL6-binding sites are associated with genes involved in many biological processes related to meristem and flower organ development. Comparison of genes associated with both ANT and AIL6 ChIP-Seq peaks and those differentially expressed after perturbation of ANT and/or AIL6 activity identified likely direct targets of ANT and AIL6 regulation. These include class B and C floral homeotic genes, growth regulatory genes, and genes involved in vascular development.

ANT and AIL6: masters of the master regulators during flower development

This article comments on: Krizek BA, Bantle AT, Heflin JM, Han H, Freese NH, Loraine AE. 2021. AINTEGUMENTA and AINTEGUMENTA-LIKE6 directly regulate floral homeotic, growth, and vascular development genes in young Arabidopsis flowers. Journal of Experimental Botany 72, 5478–5493.

LEAFY, a Pioneer Transcription Factor in Plants: A Mini-Review

A subset of eukaryotic transcription factors (TFs) possess the ability to reprogram one cell type into another. Genes important for cellular reprograming are typically located in closed chromatin, which is covered by nucleosomes. Pioneer factors are a special class of TFs that can initially engage their target sites in closed chromatin prior to the engagement with, opening of, or modification of the sites by other factors. Although many pioneer factors are known in animals, a few have been characterized in plants. The TF LEAFY (LFY) acts as a pioneer factor specifying floral fate in Arabidopsis. In response to endogenous and environmental cues, plants produce appropriate floral inducers (florigens). During the vegetative phase, LFY is repressed by the TERMINAL FLOWER 1 (TFL1)-FD complex, which functions as a floral inhibitor, or anti-florigen. The florigen FLOWERING LOCUS T (FT) competes with TFL1 to prevent the binding of the FD TF to the LFY locus. The resulting FT-FD complex functions as a transient stimulus to activate its targets. Once LFY has been transcribed in the appropriate spatiotemporal manner, LFY binds to nucleosomes in closed chromatin regions. Subsequently, LFY opens the chromatin by displacing H1 linker histones and recruiting the SWI/SNF chromatin-remodeling complex. Such local changes permit the binding of other TFs, leading to the expression of the floral meristem identity gene APETALA1. This mini-review describes the latest advances in our understanding of the pioneer TF LFY, providing insight into the establishment of gene expression competence through the shaping of the plant epigenetic landscape.

GWAS Mediated Elucidation of Heterosis for Metric Traits in Cotton (Gossypium hirsutum L.) Across Multiple Environments

For about a century, plant breeding has widely exploited the heterosis phenomenon-often considered as hybrid vigor-to increase agricultural productivity. The ensuing F₁ hybrids can substantially outperform their progenitors due to heterozygous combinations that mitigate deleterious mutations occurring in each genome. However, only fragmented knowledge is available concerning the underlying genes and processes that foster heterosis. Although cotton is among the highly valued crops, its improvement programs that involve the exploitation of heterosis are still limited in terms of significant accomplishments to make it broadly applicable in different agro-ecological zones. Here, F₁ hybrids were derived from mating a diverse Upland Cotton germplasm with commercially valuable cultivars in the Line × Tester fashion and evaluated across multiple environments for 10 measurable traits. These traits were dissected into five different heterosis types and specific combining ability (SCA). Subsequent genome-wide predictions along-with association analyses uncovered a set of 298 highly significant key single nucleotide polymorphisms (SNPs)/Quantitative Trait Nucleotides (QTNs) and 271 heterotic Quantitative Trait Nucleotides (hQTNs) related to agronomic and fiber quality traits. The integration of a genome wide association study with RNA-sequence analysis yielded 275 candidate genes in the vicinity of key SNPs/QTNs. Fiber micronaire (MIC) and lint percentage (LP) had the maximum number of associated genes, i.e., each with 45 related to QTNs/hQTNs. A total of 54 putative candidate genes were identified in association with HETEROSIS of quoted traits. The novel players in the heterosis mechanism highlighted in this study may prove to be scientifically and biologically important for cotton biologists, and for those breeders engaged in cotton fiber and yield improvement programs.

Genome-wide analysis of the AINTEGUMENTA-like (AIL) transcription factor gene family in pumpkin (Cucurbita moschata Duch.) and CmoANT1.2 response in graft union healing

AINTEGUMENTA-like (AIL) proteins are members of the APETALA 2/ETHYLENE RESPONSE FACTOR (AP2/ERF) domain family of transcription factors involved in plant growth, development, and abiotic stress responses. However, the biological functions of AIL members in pumpkin (Cucurbita moschata Duch.) remain unknown. In this study, we identified 12 AIL genes in the pumpkin genome encoding proteins predicted to be localized in the nucleus. Phylogenetic analysis showed that the AIL gene family could be classified into six major subfamilies, with each member encoding two AP2/ERF domains separated by a linker region. CmoAIL genes were expressed at varying levels in the examined tissues, and CmoANT genes showed different expression patterns under auxin (IAA), 1-naphthylphthalamic acid (NPA), and abscisic acid (ABA) treatments. Ectopic overexpression of CmoANT1.2 in Arabidopsis increased organ size and promoted growth of grafted plants by accelerating graft union formation. However, there was no significant difference at the graft junction for WT/WT and WT/ANT under IAA or NPA treatments. Taken together, the results of this study provide critical information about CmoAIL genes and their encoded proteins, and suggest future work should investigate the functions of CmoANT1.2 in the grafting process in pumpkin.

A Tissue-Specific Landscape of Alternative Polyadenylation, lncRNAs, TFs, and Gene Co-expression Networks in Liriodendron chinense

Liriodendron chinense is an economically and ecologically important deciduous tree species. Although the reference genome has been revealed, alternative polyadenylation (APA), transcription factors (TFs), long non-coding RNAs (lncRNAs), and co-expression networks of tissue-specific genes remain incompletely annotated. In this study, we used the bracts, petals, sepals, stamens, pistils, leaves, and shoot apex of L. chinense as materials for hybrid sequencing. On the one hand, we improved the annotation of the genome. We detected 13,139 novel genes, 7,527 lncRNAs, 1,791 TFs, and 6,721 genes with APA sites. On the other hand, we found that tissue-specific genes play a significant role in maintaining tissue characteristics. In total, 2,040 tissue-specific genes were identified, among which 9.2% of tissue-specific genes were affected by APA, and 1,809 tissue-specific genes were represented in seven specific co-expression modules. We also found that bract-specific hub genes were associated plant defense, leaf-specific hub genes were involved in energy metabolism. Moreover, we also found that a stamen-specific hub TF Lchi25777 may be involved in the determination of stamen identity, and a shoot-apex-specific hub TF Lchi05072 may participate in maintaining meristem characteristic. Our study provides a landscape of APA, lncRNAs, TFs, and tissue-specific gene co-expression networks in L. chinense that will improve genome annotation, strengthen our understanding of transcriptome complexity, and drive further research into the regulatory mechanisms of tissue-specific genes.

Plant cell totipotency: Insights into cellular reprogramming

Plant cells have a powerful capacity in their propagation to adapt to environmental change, given that a single plant cell can give rise to a whole plant via somatic embryogenesis without the need for fertilization. The reprogramming of somatic cells into totipotent cells is a critical step in somatic embryogenesis. This process can be induced by stimuli such as plant hormones, transcriptional regulators and stress. Here, we review current knowledge on how the identity of totipotent cells is determined and the stimuli required for reprogramming of somatic cells into totipotent cells. We highlight key molecular regulators and associated networks that control cell fate transition from somatic to totipotent cells. Finally, we pose several outstanding questions that should be addressed to enhance our understanding of the mechanisms underlying plant cell totipotency.

Morphogenic Regulators and Their Application in Improving Plant Transformation

Generation of plant lines with transgene or edited gene variants is the desired outcome of transformation technology. Conventional DNA-based plant transformation methods are the most commonly used technology but these approaches are limited to a small number of plant species with efficient transformation systems. The ideal transformation technologies are those that allow biotechnology applications across wide genetic background, especially within elite germplasm of major crop species. This chapter will briefly review key regulatory genes involved in plant morphogenesis with a focus on in vitro somatic embryogenesis and their application in improving plant transformation.

Molecular Bases for the Regulation of Adventitious Root Generation in Plants

The formation of adventitious roots (ARs) is an ecologically and economically important developmental process in plants. The evolution of AR systems is an important way for plants to cope with various environmental stresses. This review focuses on identified genes that have known to regulate the induction and initiation of ARs and offers an analysis of this process at the molecular level. The critical genes involved in adventitious rooting are the auxin signaling-responsive genes, including the AUXIN RESPONSE FACTOR (ARF) and the LATERAL ORGAN BOUNDARIES-DOMAIN (LOB) gene families, and genes associated with auxin transport and homeostasis, the quiescent center (QC) maintenance, and the root apical meristem (RAM) initiation. Several genes involved in cell wall modulation are also known to be involved in the regulation of adventitious rooting. Furthermore, the molecular processes that play roles in the ethylene, cytokinin, and jasmonic acid signaling pathways and their crosstalk modulate the generation of ARs. The crosstalk and interaction among many molecular processes generates complex networks that regulate AR generation.

Bioinformatic Tools in Arabidopsis Research

Bioinformatic tools are now an everyday part of a plant researcher's collection of protocols. They allow almost instantaneous access to large data sets encompassing genomes, transcriptomes, proteomes, epigenomes, and other "-omes," which are now being generated with increasing speed and decreasing cost. With the appropriate queries, such tools can generate quality hypotheses, sometimes without the need for new experimental data. In this chapter, we will investigate some of the tools used for examining gene expression and coexpression patterns, performing promoter analyses and functional classification enrichment for sets of genes, and exploring protein-protein and protein-DNA interactions in Arabidopsis. We will also cover additional tools that allow integration of data from several sources for improved hypothesis generation.

GRAS-Di system facilitates high-density genetic map construction and QTL identification in recombinant inbred lines of the wheat progenitor Aegilops tauschii

Due to large and complex genomes of Triticeae species, skim sequencing approaches have cost and analytical advantages for detecting genetic markers and building linkage maps. Here, we develop a high-density linkage map and identify quantitative trait loci (QTLs) for recombinant inbred lines of Aegilops tauschii, a D-genome donor of bread wheat, using the recently developed genotyping by Random Amplicon Sequencing-Direct (GRAS-Di) system, which facilitates skimming of the large and complicated genome and generates a large number of genetic markers. The deduced linkage groups based on the GRAS-Di genetic markers corresponded to the chromosome number of Ae. tauschii. We successfully identified stable QTLs for flowering time and spikelet shape-related traits. Genotype differences of RILs at the QTL-linked markers were significantly associated with the trait variations. In particular, one of the QTL-linked markers for flowering time was mapped close to VRN3 (also known as FLOWERING LOCUS T), which controls flowering. The GRAS-Di system is, therefore, an efficient and useful application for genotyping and linkage mapping in species with large and complex genomes, such as Triticeae species.

The SAP function in pistil development was proved by two allelic mutations in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

BACKGROUND

Pistil development is a complicated process in plants, and female sterile mutants are ideal material for screening and cloning pistil development-related genes. Using the female sterile mutant (fsm1), BraA04g009730.3C was previously predicted as a candidate mutant gene encoding the STERILE APETALA (SAP) transcriptional regulator. In the current study, a parallel female sterile mutant (fsm2) was derived from EMS mutagenesis of a Chinese cabbage DH line 'FT' seeds.

RESULTS

Both fsm2 and fsm1 mutant phenotypes exhibited pistil abortion and smaller floral organs. Genetic analysis indicated that the phenotype of mutant fsm2 was also controlled by a single recessive nuclear gene. Allelism testing showed that the mutated fsm1 and fsm2 genes were allelic. A single-nucleotide mutation (G-to-A) in the first exon of BraA04g009730.3C caused a missense mutation from GAA (glutamic acid) to GGA (glycine) in mutant fsm2 plants. Both allelic mutations of BraA04g009730.3C in fsm1 and fsm2 conferred the similar pistil abortion phenotype, which verified the SAP function in pistil development. To probe the mechanism of SAP-induced pistil abortion, we compared the mutant fsm1 and wild-type 'FT' pistil transcriptomes. Among the 3855 differentially expressed genes obtained, 29 were related to ovule development and 16 were related to organ size.

CONCLUSION

Our study clarified the function of BraA04g009730.3C and revealed that it was responsible for ovule development and organ size. These results lay a foundation to elucidate the molecular mechanism of pistil development in Chinese cabbage.

Fine mapping and candidate gene prediction of a major quantitative trait locus for tassel branch number in maize

Tassel branch number (TBN) is the principal component of tassel inflorescence architecture in the maize plant. TBN is believed to be controlled by a set of quantitative trait loci (QTLs). However, it is necessary to identify and genetically evaluate these QTLs before the TBN can be improved upon using a molecular breeding approach. Therefore, in this study, we developed the chromosome segment introgression line (CSIL) TBN1 with the Zong31 (Z31) background and a higher TBN, and then we utilized the CSIL-TBN1-derived populations and identified a major QTL, qTBN6a, by linkage analysis. Fine mapping of the qTBN6a QTL was validated using a set of sub-CSILs and located in a 240-kb genomic region (Bin6.07) in B73RefGen_v4. One allele included in the introgression fragment had a positive effect, noticeably increasing the TBN and demonstrating the potential to improve the TBN of Z31. Afterward, in the qTBN6a interval, gene expression, sequence alignment, functional analysis, and the analysis of motifs in the 5' UTR suggested that candidate genes of qTBN6a are important functional genes at the early stage of immature infected tassel development. Among these candidate genes, a long W22::Mu-insertion/deletion in exon one and an 11-bp insertion/deletion in the promoter region may affect the variation of the qTBN6a QTL observed between Z31 and TBN1. In addition, the candidate genes of qTBN6a were found to encode a pentatricopeptide repeat (PPR)-containing protein and a histone deacetylase (HDA), which are known to be closely associated with RNA editing and stability and chromatin state activity for the transcription of gene expression, respectively. Finally, a model of qTBN6a based on the synergistic regulation of PPR and HDA for the maintenance of inflorescence meristem (IM) identity and its differentiation to the branch meristem (BM) in TBN1 was suggested. Collectively, our results provide an available locus for the molecular improvement of TBN and the isolation of functional genes underlying this QTL.

Floral transcriptomes reveal gene networks in pineapple floral growth and fruit development

Proper flower development is essential for sexual reproductive success and the setting of fruits and seeds. The availability of a high quality genome sequence for pineapple makes it an excellent model for studying fruit and floral organ development. In this study, we sequenced 27 different pineapple floral samples and integrated nine published RNA-seq datasets to generate tissue- and stage-specific transcriptomic profiles. Pairwise comparisons and weighted gene co-expression network analysis successfully identified ovule-, stamen-, petal- and fruit-specific modules as well as hub genes involved in ovule, fruit and petal development. In situ hybridization confirmed the enriched expression of six genes in developing ovules and stamens. Mutant characterization and complementation analysis revealed the important role of the subtilase gene AcSBT1.8 in petal development. This work provides an important genomic resource for functional analysis of pineapple floral organ growth and fruit development and sheds light on molecular networks underlying pineapple reproductive organ growth.

Wang et al. perform RNA-Seq on pineapple floral samples and also use previously published RNA-Seq datasets to generate tissue- and stage-specific transcriptomic profiles. The authors use weighted gene co-expression network analysis to identify gene networks, bringing insight to underlying pineapple reproductive organ growth.

Phylogenomic analysis of the APETALA2 transcription factor subfamily across angiosperms reveals both deep conservation and lineage-specific patterns

The APETALA2 (AP2) subfamily of transcription factors are key regulators of angiosperm root, shoot, flower and embryo development. The broad diversity of anatomical and morphological structures is potentially associated with the genomic dynamics of the AP2 subfamily. However, a comprehensive phylogenomic analysis of the AP2 subfamily across angiosperms is lacking. We combined phylogenetic and synteny analysis of distinct AP2 subclades in the completed genomes of 107 angiosperm species. We identified major changes in copy number variation and genomic context within subclades across lineages, and discuss how these changes may have contributed to the evolution of lineage-specific traits. Multiple AP2 subclades show highly conserved patterns of copy number and synteny across angiosperms, while others are more dynamic and show distinct lineage-specific patterns. As examples of lineage-specific morphological divergence due to AP2 subclade dynamics, we hypothesize that loss of PLETHORA1/2 in monocots correlates with the absence of taproots, whereas independent lineage-specific changes of PLETHORA4/BABY BOOM and WRINKLED1 genes in Brassicaceae and monocots point towards regulatory divergence of embryogenesis between these lineages. Additionally, copy number expansion of TOE1 and TOE3/AP2 in asterids is implicated with differential regulation of flower development. Moreover, we show that the genomic context of AP2s is in general highly specialized per angiosperm lineage. To our knowledge, this study is the first to shed light on the evolutionary divergence of the AP2 subfamily subclades across major angiosperm lineages and emphasizes the need for lineage-specific characterization of developmental networks to understand trait variability further.

Genome-wide identification AINTEGUMENTA-like (AIL) genes in Brassica species and expression patterns during reproductive development in Brassica napus L

The AINTEGUMENTA-like (AIL) proteins, which belong to the AP2 family, play important roles in regulating the growth and development of plant organs. The AIL family has not yet been comprehensively studied in rapeseed (Brassica napus), an allotetraploid and model organism for the study of polyploid evolution. In the present study, 99 AIL family genes were identified and characterized from B. rapa, B. oleracea, B. napus, B. juncea, and B. nigra using a comprehensive genome-wide study, including analyses of phylogeny, gene structure, chromosomal localization, and expression pattern. Using a phylogenetic analysis, the AIL genes were divided into eight groups, which were closely related to the eight AtAIL genes, and which shared highly conserved structural features within the same subfamily. The non-synonymous/synonymous substitution ratios of the paralogs and orthologs were less than 1, suggesting that the AIL genes mainly experienced purifying selection during evolution. In addition, the RNA sequencing data and qRT-PCR analysis revealed that the B. napus AIL genes exhibited organ- and developmental stage-specific expression patterns. Certain genes were highly expressed in the developing seeds (BnaAIL1, BnaAIL2, BnaAIL5, and BnaAIL6), the roots (BnaANT, BnaAIL5, and BnaAIL6), and the stem (BnaAIL7B). Our results provide valuable information for further functional analysis of the AIL family in B. napus and related Brassica species.

Differential gene expression among three sex types reveals a MALE STERILITY 1 (CpMS1) for sex differentiation in papaya

BACKGROUND

Carica papaya is a trioecious plant species with a genetic sex-determination system defined by sex chromosomes. Under unfavorable environmental conditions male and hermaphrodite exhibit sex-reversal. Previous genomic research revealed few candidate genes for sex differentiation in this species. Nevertheless, more analysis is still needed to identify the mechanism responsible for sex flower organ development in papaya.

RESULTS

The aim of this study was to identify differentially expressed genes among male, female and hermaphrodite flowers in papaya during early (pre-meiosis) and later (post-meiosis) stages of flower development. RNA-seq was used to evaluate the expression of differentially expressed genes and RT-qPCR was used to verify the results. Putative functions of these genes were analyzed based on their homology with orthologs in other plant species and their expression patterns. We identified a Male Sterility 1 gene (CpMS1) highly up-regulated in male and hermaphrodite flower buds compared to female flower buds, which expresses in small male flower buds (3-8 mm), and that might be playing an important role in male flower organ development due to its homology to MS1 genes previously identified in other plants. This is the first study in which the sex-biased expression of genes related to tapetum development in the anther developmental pathway is being reported in papaya. Besides important transcription factors related to flower organ development and flowering time regulation, we identified differential expression of genes that are known to participate in ABA, ROS and auxin signaling pathways (ABA-8-hydroxylases, AIL5, UPBEAT 1, VAN3-binding protein).

CONCLUSIONS

CpMS1 was expressed in papaya male and hermaphrodite flowers at early stages, suggesting that this gene might participate in male flower organ development processes, nevertheless, this gene cannot be considered a sex-determination gene. Due to its homology with other plant MS1 proteins and its expression pattern, we hypothesize that this gene participates in anther development processes, like tapetum and pollen development, downstream gender specification. Further gene functional characterization studies in papaya are required to confirm this hypothesis. The role of ABA and ROS signaling pathways in papaya flower development needs to be further explored as well.

Genome-Wide Identification and Analysis of the AP2 Transcription Factor Gene Family in Wheat (Triticum aestivum L.)

The AP2 transcription factors play important roles in regulating plant growth and development. However, limited data are available on the contributions of AP2 transcription factors in wheat (Triticum aestivum L.). In the present study, a total of 62 AP2 genes were identified in wheat from a genome-wide search against the latest wheat genome data. Phylogenetic and sequence alignment analyses divided the wheat AP2 genes into 3 clusters, euAP2, euANT, and basalANT. Chromosomal distribution, gene structure and duplication, and motif composition were subsequently investigated. The 62 TaAP2 genes were unevenly distributed on 21 chromosomes. Twenty-four homologous gene sets among A, B, and D sub-genomes were detected, which contributed to the expansion of the wheat AP2 gene family. The expression levels of TaAP2 genes were examined using the WheatExp database; most detected genes exhibited tissue-specific expression patterns. The transcript levels of 9 randomly selected TaAP2 genes were validated through qPCR analyses. Overexpression of TaAP2-10-5D, the most likely homolog of Arabidopsis ANT gene, increased organ sizes in Arabidopsis. Our results extend our knowledge of the AP2 gene family in wheat, and contribute to further functional characterization of AP2s during wheat development with the ultimate goal of improving crop production.

Large-scale phylogenomic analysis suggests three ancient superclades of the WUSCHEL-RELATED HOMEOBOX transcription factor family in plants

The adaptation of plants to land required multiple morphological innovations. Among these include a variety of lateral organs that are initiated from apical meristems, in which the mantainance of undifferentiated stem cells is regulated by the homeodomain WUSCHEL-RELATED (WOX) transcription factors. Expansion of the WOX gene family has been associated with whole genome duplication (WGD) events and postulated to have been pivotal to the evolution of morphological complexity in land plants. Previous studies have classified the WOX gene family into three superclades (e.g., the ancient clade, the intermediate clade, and the modern clade). In order to improve our understanding of the evolution of the WOX gene family, we surveyed the WOX gene sequences from 38 genomes and 440 transcriptomes spanning the Viridiplantae and Rhodophyta. The WOX phylogeny inferred from 1039 WOX proteins drawn from 267 species with improved support along the backbone of the phylogeny suggests that the plant-specific WOX family contains three ancient superclades, which we term Type 1 (T1WOX, the WOX10/13/14 clade), Type 2 (T2WOX, the WOX8/9 and WOX11/12 clades), and Type 3 (T3WOX, the WUS, WOX1/6, WOX2, WOX3, WOX4 and WOX5/7 clades). Divergence of the T1WOX and T2WOX superclades may predate the diversification of vascular plants. Synteny analysis suggests contribution of WGD to expansion of the WOX family. Promoter analysis finds that the capacity of the WOX genes to be regulated by the auxin and cytokinin signaling pathways may be deeply conserved in the Viridiplantae. This study improves our phylogenetic context for elucidating functional evolution of the WOX gene family, which has likely contributed to the morphological complexity of land plants.

Transcriptional Regulation of Abscission Zones

Precise and timely regulation of organ separation from the parent plant (abscission) is consequential to improvement of crop productivity as it influences both the timing of harvest and fruit quality. Abscission is tightly associated with plant fitness as unwanted organs (petals, sepals, filaments) are shed after fertilization while seeds, fruits, and leaves are cast off as means of reproductive success or in response to abiotic/biotic stresses. Floral organ abscission in Arabidopsis has been a useful model to elucidate the molecular mechanisms that underlie the separation processes, and multiple abscission signals associated with the activation and downstream pathways have been uncovered. Concomitantly, large-scale analyses of omics studies in diverse abscission systems of various plants have added valuable insights into the abscission process. The results suggest that there are common molecular events linked to the biosynthesis of a new extracellular matrix as well as cell wall disassembly. Comparative analysis between Arabidopsis and soybean abscission systems has revealed shared and yet disparate regulatory modules that affect the separation processes. In this review, we discuss our current understanding of the transcriptional regulation of abscission in several different plants that has improved on the previously proposed four-phased model of organ separation.

Genome-wide investigation of the AP2/ERF gene family in tartary buckwheat (Fagopyum Tataricum)

BACKGROUND

AP2/ERF transcription factors perform indispensable functions in various biological processes, such as plant growth, development, biotic and abiotic stresses responses. The AP2/ERF transcription factor family has been identified in many plants, and several AP2/ERF transcription factors from Arabidopsis thaliana (A. thaliana) have been functionally characterized. However, little research has been conducted on the AP2/ERF genes of tartary buckwheat (Fagopyum tataricum), which is an important edible and medicinal crop. The recently published whole genome sequence of tartary buckwheat allowed us to study the tissue and expression profiles of AP2/ERF genes in tartary buckwheat on a genome-wide basis.

RESULTS

In this study, 134 AP2/ERF genes of tartary buckwheat (FtAP2/ERF) were identified and renamed according to the chromosomal distribution of the FtAP2/ERF genes. According to the number conserved domains and gene structure, the AP2/ERF genes were divided into three subfamilies by phylogenetic tree analysis, namely, AP2 (15 members), ERF (116 members) and RAV (3 members). A total of 10 motifs were detected in tartary buckwheat AP2/ERF genes, and some of the unique motifs were found to be important for the function of AP2/ERF genes.

CONCLUSION

A comprehensive analysis of AP2/ERF gene expression patterns in different tissues and fruit development stages by quantitative real-time PCR (qRT-PCR) showed that they played an important role in the growth and development of tartary buckwheat, and genes that might regulate flower and fruit development were preliminarily identified. This systematic analysis establishes a foundation for further studies of the functional characteristics of FtAP2/ERF genes and improvement of tartary buckwheat crops.

Genome-wide transcriptome analysis reveals the molecular mechanism of high temperature-induced floral abortion in Litchi chinensis

Background

Warm winter and hot spring attributed to global warming affected floral development and may induce floral abortion, resulted in poor flowering in litchi. To identify genes potentially involved in litchi floral abortion, six RNA-sequencing (RNA-Seq) libraries of the developing panicles (DPs) under low temperature (LT) conditions and the shrinking panicles (SPs) under high temperature (HT) conditions were constructed.

Results

3.07–8.97 × 10⁶ clean reads were generated. Digital expression of the DPs with that of the SPs was compared. As a result, 1320 up-regulated and 981 down-regulated differentially expressed genes (DEGs) were identified. From the enriched GO-term, 54 temperature responsive DEGs, 23 hormone homeostasis- or biosynthesis-related DEGs, 137 hormone signal transduction or responsive DEGs, and 18 flowering-related DEGs were identified. Partial Least Squares Structural Equation Modeling (PLS-SEM) analysis indicated that the effects of hormone-related DEGs on NACs, MYBs, WRKYs were stronger than that on flowering-related DEGs. Expression pattern analysis of the inflorescence in ‘Nuomici’ and ‘Huaizhi’ under LT and HT conditions showed that genes homologous to AIL6 (LcAIL6), LHY (LcLHY), MED16 (LcMED16), SKIP20 (LcSKIP20), POD20 (LcPOD20) in the two cultivars had similar expression trends.

Conclusion

This study elucidated the transcriptome in the HT-induced floral abortion and identified key genes involved in the process. NACs, MYBs, WRKYs may act as central players involved in the HT-induced floral abortion underlying hormonal control. Increased transcript in LcLHY, LcMED16, LcSKIP20, LcPOD20 and decreased transcript in LcAIL6 might be related to the inhibition of floral development. Our studies provided potential genes for the future molecular breeding of new cultivars that can reduce floral abortion under warm climates, and a novel clue to reveal the relationship of biological processes based on the RNA-seq data using PLS-SEM.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5493-8) contains supplementary material, which is available to authorized users.