The interplay between extracellular and intercellular auxin signaling in plants.

The phytohormone auxin exerts control over remarkable developmental processes in plants. It moves from cell to cell, resulting in the creation of both extracellular auxin and intracellular auxin, which are recognized by distinct auxin receptors. These two auxin signaling systems govern different auxin responses while working together to regulate plant development. In this review, we outline the latest research advancements in unraveling these auxin signaling pathways, encompassing auxin perception and signaling transductions. We emphasize the interaction between extracellular auxin and intercellular auxin, which contributes to the intricate role of auxin in plant development.

Atmospheric nitrogen dioxide suppresses the activity of phytochrome interacting factor 4 to suppress hypocotyl elongation.

MAIN CONCLUSION: Ambient concentrations of atmospheric nitrogen dioxide (NO2) inhibit the binding of PIF4 to promoter regions of auxin pathway genes to suppress hypocotyl elongation in Arabidopsis. Ambient concentrations (10-50 ppb) of atmospheric nitrogen dioxide (NO2) positively regulate plant growth to the extent that organ size and shoot biomass can nearly double in various species, including Arabidopsis thaliana (Arabidopsis). However, the precise molecular mechanism underlying NO2-mediated processes in plants, and the involvement of specific molecules in these processes, remain unknown. We measured hypocotyl elongation and the transcript levels of PIF4, encoding a bHLH transcription factor, and its target genes in wild-type (WT) and various pif mutants grown in the presence or absence of 50 ppb NO2. Chromatin immunoprecipitation assays were performed to quantify binding of PIF4 to the promoter regions of its target genes. NO2 suppressed hypocotyl elongation in WT plants, but not in the pifq or pif4 mutants. NO2 suppressed the expression of target genes of PIF4, but did not affect the transcript level of the PIF4 gene itself or the level of PIF4 protein. NO2 inhibited the binding of PIF4 to the promoter regions of two of its target genes, SAUR46 and SAUR67. In conclusion, NO2 inhibits the binding of PIF4 to the promoter regions of genes involved in the auxin pathway to suppress hypocotyl elongation in Arabidopsis. Consequently, PIF4 emerges as a pivotal participant in this regulatory process. This study has further clarified the intricate regulatory mechanisms governing plant responses to environmental pollutants, thereby advancing our understanding of how plants adapt to changing atmospheric conditions.

Metabolomic and transcriptomic analyses of peach leaves and fruits in response to pruning.

BACKGROUND: Pruning is an important cultivation management option that has important effects on peach yield and quality. However, the effects of pruning on the overall genetic and metabolic changes in peach leaves and fruits are poorly understood. RESULTS: The transcriptomic and metabolomic profiles of leaves and fruits from trees subjected to pruning and unpruning treatments were measured. A total of 20,633 genes and 622 metabolites were detected. Compared with those in the control, 1,127 differentially expressed genes (DEGs) and 77 differentially expressed metabolites (DEMs) were identified in leaves from pruned and unpruned trees (pdLvsupdL), whereas 423 DEGs and 29 DEMs were identified in fruits from the pairwise comparison pdFvsupdF. The content of three auxin analogues was upregulated in the leaves of pruned trees, the content of all flavonoids detected in the leaves decreased, and the expression of almost all genes involved in the flavonoid biosynthesis pathway decreased. The phenolic acid and amino acid metabolites detected in fruits from pruned trees were downregulated, and all terpenoids were upregulated. The correlation analysis revealed that DEGs and DEMs in leaves were enriched in tryptophan metabolism, auxin signal transduction, and flavonoid biosynthesis. DEGs and DEMs in fruits were enriched in flavonoid and phenylpropanoid biosynthesis, as well as L-glutamic acid biosynthesis. CONCLUSIONS: Pruning has different effects on the leaves and fruits of peach trees, affecting mainly the secondary metabolism and hormone signalling pathways in leaves and amino acid biosynthesis in fruits.

A Single-step Generation of AlissAID-based Conditional Knockdown Strains Using Nanobody that Targets GFP or mCherry in Budding Yeast.

The Auxin-inducible degron (AID) system is a genetic tool that induces rapid target protein depletion in an auxin-dependent manner. Recently, two advanced AID systems-the super-sensitive AID and AID 2-were developed using an improved pair of synthetic auxins and mutated TIR1 proteins. In these AID systems, a nanomolar concentration of synthetic auxins is sufficient as a degradation inducer for target proteins. However, despite these advancements, AID systems still require the fusion of an AID tag to the target protein for degradation, potentially affecting its function and stability. To address this limitation, we developed an affinity linker-based super-sensitive AID (AlissAID) system using a single peptide antibody known as a nanobody. In this system, the degradation of GFP- or mCherry-tagged target proteins is induced in a synthetic auxin (5-Ad-IAA)-dependent manner. Here, we introduce a simple method for generating AlissAID strains targeting GFP or mCherry fusion proteins in budding yeasts. Key features • AlissAID system enables efficient degradation of the GFP or mCherry fusion proteins in a 5-Ad-IAA-depending manner. • Transforming the pAlissAID plasmids into strains with GFP- or mCherry- tagged proteins.

Hierarchical global and local auxin signals coordinate cellular interdigitation in Arabidopsis.

The development of multicellular tissues requires both local and global coordination of cell polarization, however, the mechanisms underlying their interplay are poorly understood. In Arabidopsis, leaf epidermal pavement cells (PC) develop a puzzle-piece shape locally coordinated through apoplastic auxin signaling. Here we show auxin also globally coordinates interdigitation by activating the TIR1/AFB-dependent nuclear signaling pathway. This pathway promotes a transient maximum of auxin at the cotyledon tip, which then moves across the leaf activating local PC polarization, as demonstrated by locally uncaged auxin globally rescuing defects in tir1;afb1;afb2;afb4;afb5 mutant but not in tmk1;tmk2;tmk3;tmk4 mutants. Our findings show that hierarchically integrated global and local auxin signaling systems, which respectively depend on TIR1/AFB-dependent gene transcription in the nucleus and TMK-mediated rapid activation of ROP GTPases at the cell surface, control PC interdigitation patterns in Arabidopsis cotyledons, revealing a mechanism for coordinating a local cellular process with the development of whole tissues.

Nucleolin acute degradation reveals novel functions in cell cycle progression and division in TNBC.

Nucleoli are large nuclear sub-compartments where vital processes, such as ribosome assembly, take place. Technical obstacles still limit our understanding of the biological functions of nucleolar proteins in cell homeostasis and cancer pathogenesis. Since most nucleolar proteins are essential, their abrogation cannot be achieved through conventional approaches. Additionally, the biological activities of many nucleolar proteins are connected to their physiological concentration. Thus, artificial overexpression might not fully recapitulate their endogenous functions. Proteolysis-based approaches, such as the Auxin Inducible Degron (AID) system paired with CRISPR/Cas9 knock-in gene-editing, have the potential to overcome these limitations, providing unprecedented characterization of the biological activities of endogenous nucleolar proteins. We applied this system to endogenous nucleolin (NCL), one of the most abundant nucleolar proteins, and characterized the impact of its acute depletion on Triple-Negative Breast Cancer (TNBC) cell behavior. Abrogation of endogenous NCL reduced proliferation and caused defective cytokinesis, resulting in bi-nucleated tetraploid cells. Bioinformatic analysis of patient data, and quantitative proteomics using our experimental NCL-depleted model, indicated that NCL levels are correlated with the abundance of proteins involved in chromosomal segregation. In conjunction with its effects on sister chromatid dynamics, NCL abrogation enhanced the anti-proliferative effects of chemical inhibitors of mitotic modulators such as the Anaphase Promoting Complex. In summary, using the AID system in combination with CRISPR/Cas9 for endogenous gene editing, our findings indicate a novel role for NCL in supporting the completion of the cell division in TNBC models, and that its abrogation could enhance the therapeutic activity of mitotic-progression inhibitors.

The auxin response factor (ARF) gene family in Cyclocarya paliurus: genome-wide identification and their expression profiling under heat and drought stresses.

Auxin response factors (ARFs), as the main components of auxin signaling, play a crucial role in various processes of plant growth and development, as well as in stress response. So far, there have been no reports on the genome-wide identification of the ARF transcription factor family in Cyclocarya paliurus, a deciduous tree plant in the family Juglaceae. In this study, a total of 34 CpARF genes were identified based on whole genome sequence, and they were unevenly distributed on 16 chromosomes, with the highest distribution on chromosome 6. Domain analysis of CpARF proteins displayed that 31 out of 34 CpARF proteins contain a typical B3 domain (DBD domain), except CpARF12/ CpARF14/CpARF31, which all belong to Class VI. And 20 CpARFs (58.8%) contain an auxin_IAA binding domain, and are mainly distributed in classes I, and VI. Phylogenetic analysis showed that CpARF was divided into six classes (I-VI), each containing 4, 4, 1, 8, 4, and 13 members, respectively. Gene duplication analysis showed that there are 14 segmental duplications and zero tandem repeats were identified in the CpARF gene family of the C. paliurus genome. The Ka/Ks ratio of duplicate gene pairs indicates that CpARF genes are subjected to strong purification selection pressure. Synteny analysis showed that C. paliurus shared the highest homology in 74 ARF gene pairs with Juglans regia, followed by 73, 51, 25, and 11 homologous gene pairs with Populus trichocarpa, Juglans cathayensis, Arabidopsis, and rice, respectively. Promoter analysis revealed that 34 CpARF genes had cis-elements related to hormones, stress, light, and growth and development except for CpARF12. The expression profile analysis showed that almost all CpARF genes were differentially expressed in at least one tissue, and several CpARF genes displayed tissue-specific expression. Furthermore, 24 out of the 34 CpARF genes have significantly response to drought stress (P < 0.05), and most of them (16) being significantly down-regulated under moderate drought treatment. Meanwhile, the majority of CpARF genes (28) have significantly response to drought stress (P < 0.05), and most of them (26) are significantly down-regulated under severe drought treatment. Furthermore, 32 out of the 34 CpARF genes have significantly response to high, middle, and low salt stress under salt treatment (P < 0.05). Additionally, subcellular localization analysis confirmed that CpARF16 and CpARF32 were all localized to nucleus. Thus, our findings expand the understanding of the function of CpARF genes and provide a basis for further functional studies on CpARF genes in C. paliurus. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-024-01474-1.

AZGs: a new family of cytokinin transporters.

Cytokinins (CKs) are phytohormones structurally similar to purines that play important roles in various aspects of plant physiology and development. The local and long-distance distribution of CKs is very important to control their action throughout the plant body. Over the past decade, several novel CK transporters have been described, many of which have been linked to a physiological function rather than simply their ability to transport the hormone in vitro. Purine permeases, equilibrative nucleotide transporters and ATP-binding cassette transporters are involved in the local and long-range distribution of CK. In addition, members of the Arabidopsis AZA-GUANINE RESISTANT (AZG) protein family, AZG1 and AZG2, have recently been shown to mediate CK uptake at the plasma membrane and endoplasmic reticulum. Despite sharing ∼50% homology, AZG1 and AZG2 have unique transport mechanisms, tissue-specific expression patterns, and subcellular localizations that underlie their distinct physiological functions. AZG2 is expressed in a small group of cells in the overlying tissue around the lateral root primordia, where its expression is induced by auxins and it is involved in the regulation of lateral root growth. AZG1 is ubiquitously expressed, with high levels in the division zone of the root apical meristem. Here, it binds and stabilises the auxin efflux carrier PIN1, thereby shaping root architecture, particularly under salt stress. This review highlights the latest findings on the protein properties, transport mechanisms and cellular functions of this new family of CK transporters and discusses perspectives for future research in this field.

OsMYB14, an R2R3-MYB Transcription Factor, Regulates Plant Height through the Control of Hormone Metabolism in Rice.

Plant growth must be regulated throughout the plant life cycle. The MYB TF family is one of the largest TF families and is involved in metabolism, lignin biosynthesis and developmental processes. Here, we showed that OsMYB14, a rice R2R3-MYB TF, was expressed in leaves and roots, especially in rice culm and panicles, and that it localized to the nucleus. Overexpression of OsMYB14 (OsMYB14-ox) in rice resulted in a 30% reduction in plant height compared to that of the wild type (WT), while the height of the osmyb14-ko mutant generated using the CRISPR/Cas9 system was not significantly different. Microscopic observations of the first internode revealed that the cell size did not differ significantly among the lines. RNA-seq analysis revealed that genes associated with plant development, regulation, lipid metabolism, carbohydrate metabolism, and gibberellin and auxin metabolic processes were downregulated in the OsMYB14-ox line. Hormone quantitation revealed that inactive GA19 accumulated in OsMYB14-ox but not in the WT or knockout plants, suggesting that GA20 generation was repressed. IAA and IAA-Asp accumulated in OsMYB14-ox and osmyb14-ko, respectively. Indeed, real-time PCR analysis revealed that the expression of OsGA20ox1, encoding Gibberellin20 oxidase 1, and OsGH3-2, encoding IAA-amido synthetase, was downregulated in OsMYB14-ox and upregulated in osmyb14-ko. A protein binding microarray (PBM) revealed the presence of a consensus DNA-binding sequence, the ACCTACC-like motif, in the promoters of the OsGA20ox1 and GA20ox2 genes. These results suggest that OsMYB14 may act as a negative regulator of biological processes affecting plant height in rice by regulating GA biosynthesis and auxin metabolism.

Integrated Methylome and Transcriptome Analysis between Wizened and Normal Flower Buds in Pyrus pyrifolia Cultivar 'Sucui 1'.

Here, cytosine methylation in the whole genome of pear flower buds was mapped at a single-base resolution. There was 19.4% methylation across all sequenced C sites in the Pyrus pyrifolia cultivar 'Sucui 1' flower bud genome. Meantime, the CG, CHG, and CHH sequence contexts (where H = A, T or C) exhibited 47.4%, 33.3%, and 11.9% methylation, respectively. Methylation in different gene regions was revealed through combining methylome and transcriptome analysis, which presented various transcription trends. Genes with methylated promoters exhibited lower expression levels than genes with non-methylated promoters, while body-methylated genes displayed an obvious negative correlation with their transcription levels. The methylation profiles of auxin- and cytokinin-related genes were estimated. And some of them proved to be hypomethylated, with increased transcription levels, in wizened buds. More specifically, the expression of the genes PRXP73, CYP749A22, and CYP82A3 was upregulated as a result of methylation changes in their promoters. Finally, auxin and cytokinin concentrations were higher in wizened flower buds than in normal buds. The exogenous application of paclobutrazol (PP333) in the field influenced the DNA methylation status of some genes and changed their expression level, reducing the proportion of wizened flower buds in a concentration-dependent manner. Overall, our results demonstrated the relationship between DNA methylation and gene expression in wizened flower buds of P. pyrifolia cultivar 'Sucui 1', which was associated with changes in auxin and cytokinin concentrations.

Low-oxygen-induced root bending is altered by phytoglobin1 through mediation of ethylene response factors (ERFs) and auxin signaling.

MAIN CONCLUSION: phytoglobin1 positively regulates root bending in hypoxic Arabidopsis roots through regulation of ethylene response factors and auxin transport. Hypoxia-induced root bending is known to be mediated by the redundant activity of the group VII ethylene response factors (ERFVII) RAP2.12 and HRE2, causing changes in polar auxin transport (PAT). Here, we show that phytoglobin1 (Pgb1), implicated in hypoxic adaptation through scavenging of nitric oxide (NO), can alter root direction under low oxygen. Hypoxia-induced bending is exaggerated in roots over-expressing Pgb1 and attenuated in those where the gene is suppressed. These effects were attributed to Pgb1 repressing both RAP2.12 and HRE2. Expression, immunological and genetic data place Pgb1 upstream of RAP2.12 and HRE2 in the regulation of root bending in oxygen-limiting environments. The attenuation of slanting in Pgb1-suppressing roots was associated with depletion of auxin activity at the root tip because of depression in PAT, while exaggeration of root bending in Pgb1-over-expressing roots with the retention of auxin activity. Changes in PIN2 distribution patterns, suggestive of redirection of auxin movement during hypoxia, might contribute to the differential root bending responses of the transgenic lines. In the end, Pgb1, by regulating NO levels, controls the expression of 2 ERFVIIs which, in a cascade, modulate PAT and, therefore, root bending.

ZmSPL10, ZmSPL14 and ZmSPL26 act together to promote stigmatic papilla formation in maize through regulating auxin signaling and ZmWOX3A expression.

Maize silk is a specialized type of stigma, covered with numerous papillae for pollen grain capture. However, the developmental process of stigmatic papillae and the underlying regulatory mechanisms have remained largely unknown. Here, we combined the cytological, genetic and molecular studies to demonstrate that three homologous genes ZmSPL10, ZmSPL14 and ZmSPL26 play a central role in promoting stigmatic papilla formation in maize. We show that their triple knockout mutants are nearly complete lack of stigmatic papilla, resulting in a severe reduction in kernel setting. Cellular examination reveals that stigmatic papilla is developed from a precursor cell, which is the smaller daughter cell resulting from asymmetric cell division of a silk epidermal cell. In situ hybridization shows that ZmSPL10, ZmSPL14 and their target genes SPI1, ZmPIN1b, ZmARF28 and ZmWOX3A are preferentially expressed in the precursor cells of stigmatic papillae. Moreover, ZmSPL10, ZmSPL14 and ZmSPL26 directly bind to the promoters of SPI1, ZmPIN1b, ZmARF28 and ZmWOX3A and promote their expression. Further, Zmwox3a knockout mutants display severe defects in stigmatic papilla formation and reduced seed setting. Collectively, our results demonstrate that ZmSPL10, ZmSPL14 and ZmSPL26 act together to promote stigmatic papilla development through regulating auxin signaling and ZmWOX3A expression.

BIG coordinates auxin and SHORT ROOT to promote asymmetric stem cell divisions in Arabidopsis roots.

KEY MESSAGE: BIG regulates ground tissue formative divisions by bridging the auxin gradient with SHR abundance in Arabidopsis roots. The formative divisions of cortex/endodermis initials (CEIs) and CEI daughter cells (CEIDs) in Arabidopsis roots are coordinately controlled by the longitudinal auxin gradient and the radial SHORT ROOT (SHR) abundance. However, the mechanism underlying this coordination remains poorly understood. In this study, we demonstrate that BIG regulates ground tissue formative divisions by bridging the auxin gradient with SHR abundance. Mutations in BIG gene repressed cell cycle progression, delaying the formative divisions within the ground tissues and impairing the establishment of endodermal and cortical identities. In addition, we uncovered auxin's suppressive effect on BIG expression, triggering CYCLIND6;1 (CYCD6;1) activation in an SHR-dependent fashion. Moreover, the degradation of RETINOBLASTOMA-RELATED (RBR) is jointly regulated by BIG and CYCD6;1. The loss of BIG function led to RBR protein accumulation, detrimentally impacting the SHR/SCARECROW (SCR) protein complex and the CEI/CEID formative divisions. Collectively, these findings shed light on a fundamental mechanism wherein BIG intricately coordinates the interplay between SHR/SCR and auxin, steering ground tissue patterning within Arabidopsis root tissue.

Tip of the iceberg? Three novel TOPLESS-interacting effectors of the gall-inducing fungus Ustilago maydis.

Ustilago maydis is a biotrophic pathogen causing smut disease in maize. It secretes a cocktail of effector proteins, which target different host proteins during its biotrophic stages in the host plant. One such class of proteins we identified previously is TOPLESS (TPL) and TOPLESS-RELATED (TPR) transcriptional corepressors. Here, we screened 297 U. maydis effector candidates for their ability to interact with maize TPL protein RAMOSA 1 ENHANCER LOCUS 2 LIKE 2 (RELK2) and their ability to induce auxin signaling and thereby identified three novel TPL-interacting protein effectors (Tip6, Tip7, and Tip8). Structural modeling and mutational analysis allowed the identification of TPL-interaction motifs of Tip6 and Tip7. In planta interaction between Tip6 and Tip7 with RELK2 occurs mainly in nuclear compartments, whereas Tip8 colocalizes with RELK2 in a compartment outside the nucleus. Overexpression of Tip8 in nonhost plants leads to cell death, indicating recognition of the effector or its activity. By performing infection assays with single and multideletion mutants of U. maydis, we demonstrate a positive role of Tip6 and Tip7 in U. maydis virulence. Transcriptional profiling of maize leaves infected with Tip effector mutants in comparison with SG200 strain suggests Tip effector activities are not merely redundant.

Putting heads together: Developmental genetics of the Asteraceae capitulum.

Inflorescence architecture is highly variable across plant lineages yet is critical for facilitating reproductive success. The capitulum-type inflorescence of the Asteraceae is marked as a key morphological innovation that preceded the family's diversification and expansion. Despite its evolutionary significance, our understanding of capitulum development and evolution is limited. This review highlights our current perspective on capitulum evolution through the lens of both its molecular and developmental underpinnings. We attempt to summarize our understanding of the capitulum by focusing on two key characteristics: patterning (arrangement of florets on a capitulum) and floret identity specification. Note that these two features are interconnected such that the identity of florets depends on their position along the inflorescence axis. Phytohormones such as auxin seemingly determine both pattern progression and floret identity specification through unknown mechanisms. Floret morphology in a head is controlled by differential expression of floral symmetry genes regulating floret identity specification. We briefly summarize the applicability of the ABCE quartet model of flower development in regulating the floret organ identity of a capitulum in Asteraceae. Overall, there have been promising advancements in our understanding of capitula; however, comprehensive functional genetic analyses are necessary to fully dissect the molecular pathways and mechanisms involved in capitulum development.

VIK-Mediated Auxin Signaling Regulates Lateral Root Development in Arabidopsis.

The crucial role of TIR1-receptor-mediated gene transcription regulation in auxin signaling has long been established. In recent years, the significant role of protein phosphorylation modifications in auxin signal transduction has gradually emerged. To further elucidate the significant role of protein phosphorylation modifications in auxin signaling, a phosphoproteomic analysis in conjunction with auxin treatment has identified an auxin activated Mitogen-activated Protein Kinase Kinase Kinase (MAPKKK) VH1-INTERACTING Kinase (VIK), which plays an important role in auxin-induced lateral root (LR) development. In the vik mutant, auxin-induced LR development is significantly attenuated. Further investigations show that VIK interacts separately with the positive regulator of LR development, LATERAL ORGAN BOUNDARIES-DOMAIN18 (LBD18), and the negative regulator of LR emergence, Ethylene Responsive Factor 13 (ERF13). VIK directly phosphorylates and stabilizes the positive transcription factor LBD18 in LR formation. In the meantime, VIK directly phosphorylates the negative regulator ERF13 at Ser168 and Ser172 sites, causing its degradation and releasing the repression by ERF13 on LR emergence. In summary, VIK-mediated auxin signaling regulates LR development by enhancing the protein stability of LBD18 and inducing the degradation of ERF13, respectively.

New insights into plasmodesmata: complex 'protoplasmic connecting threads'.

Intercellular communication in plants, as in other multicellular organisms, allows cells in tissues to coordinate their responses for development and in response to environmental stimuli. Much of this communication is facilitated by plasmodesmata (PD), consisting of membranes and cytoplasm, that connect adjacent cells to each other. PD have long been viewed as passive conduits for the movement of a variety of metabolites and molecular cargoes, but this perception has been changing over the last two decades or so. Research from the last few years has revealed the importance of PD as signaling hubs and as crucial players in hormone signaling. The adoption of advanced biochemical approaches, molecular tools and high-resolution imaging modalities have led to several recent breakthroughs in our understanding of the roles of PD, revealing the structural and regulatory complexity of these 'protoplasmic connecting threads'. We highlight several of these findings that we think well illustrate the current understanding of PD as functioning at the nexus of plant physiology, development, and acclimation to the environment.

Quantitative imaging reveals the role of MpARF proteasomal degradation during gemma germination.

The auxin signaling molecule controls a variety of growth and developmental processes in land plants. Auxin regulates gene expression through a nuclear auxin signaling pathway (NAP) consisting of a ubiquitin ligase auxin receptor TIR1/AFB, its Aux/IAA degradation substrate, and DNA-binding ARF transcription factors. While extensive qualitative understanding of the pathway and its interactions has been obtained, mostly by studying the flowering plant Arabidopsis thaliana, it is so far unknown how these translate to quantitative system behaviour in vivo, a problem that is confounded by large NAP gene families in most species. Here we used the minimal NAP of the liverwort Marchantia polymorpha to quantitatively map NAP protein accumulation and dynamics in vivo through the use of knock-in fluorescent fusion proteins. Beyond revealing the dynamic native accumulation profile of the entire NAP protein network, we discovered that the two central ARFs, MpARF1 and MpARF2, are proteasomally degraded. This auxin-independent degradation tunes ARF protein stoichiometry to favor gene activation, thereby reprogramming auxin response during developmental progression. Thus, quantitative analysis of the entire NAP allowed us to identify ARF degradation and stoichiometries of activator and repressor ARFs as a potential mechanism for controlling gemma germination.

Demequina capsici sp. nov., a novel plant growth-promoting actinomycete isolated from the rhizosphere of bell pepper (Capsicum annuum).

Demequina, commonly found in coastal and marine environments, represents a genus of Actinomycetes. In this study, strains Demequina PMTSA13T and OYTSA14 were isolated from the rhizosphere of Capsicum annuum, leading to the discovery of a novel species, Demequina capsici. Bacteria play a significant role in plant growth, yet there have been no reports of the genus Demequina acting as plant growth-promoting bacteria (PGPB). Comparative genomics analysis revealed ANI similarity values of 74.05-80.63% for PMTSA13T and 74.02-80.54% for OYTSA14, in comparison to various Demequina species. The digital DNA-DNA hybridization (dDDH) values for PMTSA13T ranged from 19 to 39%, and 19.1-38.6% for OYTSA14. Genome annotation revealed the presence of genes associated with carbohydrate metabolism and transport, suggesting a potential role in nutrient cycling and availability for plants. These strains were notably rich in genes related to 'carbohydrate metabolism and transport (G)', according to their Cluster of Orthologous Groups (COG) classification. Additionally, both strains were capable of producing auxin (IAA) and exhibited enzymatic activities for cellulose degradation and catalase. Furthermore, PMTSA13T and OYTSA14 significantly induced the growth of Arabidopsis thaliana seedlings primarily attributed to their capacity to produce IAA, which plays a crucial role in stimulating plant growth and development. These findings shed light on the potential roles of Demequina strains in plant-microbe interactions and agricultural applications. The type strain is Demequina capsici PMTSA13T (= KCTC 59028T = GDMCC 1.4451T), meanwhile OYTSA14 is identified as different strains of Demequina capsici.

Alternate bearing in 'Hass' avocado - Fruit load-induced changes in bud auxin homeostasis are associated with flowering repression.

In 'Hass' avocado (Persea americana), fruit presence reduces next season flowering. Recent fruit tree studies proposed that heavy fruit load (HFL) generates an auxin (IAA) signal in the buds, which represses flowering. However, the nature of this signal remains unknown. Here, we investigated the effect of avocado HFL on bud IAA accumulation and flowering transition. We found that IAA-aspartate and IAA-glutamate conjugate levels were significantly higher in buds from 'on' (fully loaded) than 'off' (low-loaded) trees, hinting that free IAA levels were higher in the former. Expression analysis showed that coinciding with flowering reduction, HFL induced the floral repressor PaTFL1, and suggested that accumulation of IAA in buds as imposed by HFL was associated with its conjugation to aspartate and glutamate and resulted both from de novo IAA synthesis, as well as from reduced IAA export. Accordingly, experiments involving radiolabelled 14C-IAA demonstrated that HFL reduced shoot basipetal IAA transport. Lastly, we confirmed the negative effects of IAA on flowering, showing that IAA and PAT blocker (TIBA) treatments delayed 'off' trees inflorescence development, reducing their inflorescence axis and inducing PaTFL1 transcript. Together, our data suggest that avocado HFL generates IAA signalling in buds that induces PaTFL1, which represses inflorescence development.