Auxin Response Factor Research Articles

Identification and characterization of the auxin-response factor family in moso bamboo reveals that PeARF41 negatively regulates second cell wall formation.

Auxin response factors (ARFs) are key transcriptional factors mediating the transcriptional of auxin-related genes that play crucial roles in a range of plant metabolic activities. The characteristics of 47 PeARFs, identified in moso bamboo and divided into three classes, were evaluated. Structural feature analysis showed that intron numbers ranged from 3 to 14, while Motif 1, 2, 7 and 10 were highly conserved, altogether forming DNA-binding and ARF domains. Analysis of RNA-seq from different tissues revealed that PeARFs showed tissue-specificity. Additionally, abundant hormone-response and stress-related elements were enriched in promoters of PeARFs, supporting the hypothesis that the expression of PeARFs was significantly activated or inhibited by ABA and cold treatments. Further, PeARF41 overexpression inhibited SCW formation by reducing hemicellulose, cellulose and lignin contents. Moreover, a co-expression network, containing 28 genes with PeARF41 at its core was predicted, and the results of yeast one hybridization (Y1H), electrophoretic mobility shift assay (EMSA) and dual-luciferase (Dul-LUC) assays showed that PeARF41 bound the PeSME1 promoter to inhibit its expression. We conclude that a 'PeARF41-PeSME1' regulatory cascade mediates SCW formation. Our findings provided a solid theoretical foundation for further research on the role of PeARFs.

Inhibition of histone deacetylase in Arabidopsis root calli promotes de novo shoot organogenesis

De novo organogenesis from somatic cells to the entire plant represents a remarkable biological phenomenon, but the underlying regulatory mechanism, particularly at the epigenetic level, remains obscure. In this work, we demonstrate the important role of histone deacetylases (HDACs) in shoot organogenesis. HDAC inhibition by trichostatin A (an HDAC inhibitor) at the callus induction stage promotes shoot formation in wounded roots and circumvents tissue wounding to initiate shoot regeneration in unwounded roots. This HDAC inhibition-mediated promotion of shoot organogenesis in wounded roots is associated with the concomitant upregulation of the wound signaling pathway (WOUND INDUCED DEDIFFERENTIATION 4, ENHANCER OF SHOOT REGENERATION1, ISOPENTENYLTRANSFERASE 5, CUP-SHAPED COTYLEDON 2 etc.) and the ARF-LBD pathway (AUXIN RESPONSE FACTOR 19, LATERAL ORGAN BOUNDARIES-DOMAIN 29, etc.) and the downregulation of auxin biosynthesis and reduced auxin content. Furthermore, inhibiting HDACs enhances the local enrichment of histone 3 lysine 9/lysine 14 acetylation at ISOPENTENYLTRANSFERASE 5, supporting the role of histone acetylation in its transcriptional regulation. On the other hand, the HDAC inhibition-associated activation of shoot organogenesis from unwounded roots is coupled with increased expression of the ARF-LBD pathway gene LATERAL ORGAN BOUNDARIES-DOMAIN 29 while bypassing the wound signaling or auxin biosynthetic genes. These findings provide novel insights into the regulatory mechanisms underlying de novo shoot organogenesis and lay a foundation for the improvement of plant transformation technologies.

The whole-genome dissection of root system architecture provides new insights for the genetic improvement of alfalfa (Medicago sativa L.).

Appropriate root system architecture (RSA) can improve alfalfa yield, yet its genetic basis remains largely unexplored. This study evaluated six RSA traits in 171 alfalfa genotypes grown under controlled greenhouse conditions. We also analyzed five yield-related traits in normal and drought stress environments and found a significant correlation (0.50) between root dry weight (RDW) and alfalfa dry weight under normal conditions (N_DW). A genome-wide association study (GWAS) was performed using 1 303 374 single-nucleotide polymorphisms (SNPs) to explore the relationships between RSA traits. Sixty significant SNPs (-log 10 (P) ≥ 5) were identified, with genes within the 50kb upstream and downstream ranges primarily enriched in GO terms related to root development, hormone synthesis, and signaling, as well as morphological development. Further analysis identified 19 high-confidence candidate genes, including AUXIN RESPONSE FACTORs (ARFs), LATERAL ORGAN BOUNDARIES-DOMAIN (LBD), and WUSCHEL-RELATED HOMEOBOX (WOX). We verified that the forage dry weight under both normal and drought conditions exhibited significant differences among materials with different numbers of favorable haplotypes. Alfalfa containing more favorable haplotypes exhibited higher forage yields, whereas favorable haplotypes were not subjected to human selection during alfalfa breeding. Genomic prediction (GP) utilized SNPs from GWAS and machine learning for each RSA trait, achieving prediction accuracies ranging from 0.70 for secondary root position (SRP) to 0.80 for root length (RL), indicating robust predictive capability across the assessed traits. These findings provide new insights into the genetic underpinnings of root development in alfalfa, potentially informing future breeding strategies aimed at improving yield.

The Identification of Auxin Response Factors and Expression Analyses of Different Floral Development Stages in Roses.

Background/Objectives:Auxin response factors (ARFs) are important in plant growth and development, especially flower development. However, there is limited research on the comprehensive identification and characterization of ARF genes in roses. Methods: We employed bioinformatics tools to identify the ARF genes of roses. These genes were characterized for their phylogenetic relationships, chromosomal positions, conserved motifs, gene structures, and expression patterns. Results: In this study, a total of 17 ARF genes were identified in the genomes of Rosa chinensis 'OB', R. chinensis 'CH', R. rugosa, and R. wichurana. Based on RNA-seq analyses, we found that the ARF genes had diverse transcript patterns in various tissues and cultivars. In 'CH', the expression levels of RcCH_ARFs during different flower-development stages were classified into four clusters. In cluster 3 and cluster 4, RcCH_ARFs were specifically high and low in different stages of floral evocation. Gene expression and phylogenetic analyses showed that RcCH_ARF3, RcCH_ARF4, and RcCH_ARF18 were likely to be the key genes for rose flower development. Conclusions: The identification and characterization of ARF genes in Rosa were investigated. The results presented here provide a theoretical basis for the molecular mechanisms of ARF genes in plant development and flowering for roses, with a broader application for other species in the rose family and for the development of novel cultivars.

Feedback regulation of m6A modification creates local auxin maxima essential for rice microsporogenesis.

N6-methyladenosine (m6A) RNA modification and its effectors control various plant developmental processes, yet whether and how these effectors are transcriptionally controlled to confer functional specificity so far remain elusive. Herein, we show that a rice C2H2 zinc-finger protein, OsZAF, specifically activates the expression of OsFIP37 encoding a core component of the m6A methyltransferase complex during microsporogenesis in rice anthers. OsFIP37, in turn, facilitates m6A modification and stabilization of an auxin biosynthesis gene OsYUCCA3 to promote auxin biosynthesis in anthers. This elevates auxin levels coinciding with upregulation of an auxin response factor OsARF12 that positively controls OsZAF, thus creating a positive feedback circuit whereby OsFIP37 is continuously activated for local auxin production. Our findings suggest that OsZAF-dependent feedback regulation of m6A modification is integral to local auxin biosynthesis and signaling in anthers, which facilitates the timely generation of auxin maxima required for male meiosis in rice.

Genome-wide characterization of auxin response factor (ARF) genes in bermudagrass and ectopically functional analysis of CdARF6-B2 gene in Arabidopsis

Genome-wide characterization of auxin response factor (ARF) genes in bermudagrass and ectopically functional analysis of CdARF6-B2 gene in Arabidopsis

The effects of different hormone combinations on the growth of Panax notoginseng anther callus based on metabolome analysis

Panax notoginseng saponins (PNS), the primary active components of Panax notoginseng (Burk.) F.H.Chen, a traditional and precious Chinese medicinal herb, are mainly derived from the roots of the plant. However, due to the long cultivation period and specific environmental requirements, the PNS supply is often limited. And, callus cultures of P. notoginseng, which grow rapidly, have short production cycles, and can be cultured under controlled conditions, provide a more efficient source for the quick acquisition of saponins. In this study, anthers of P. notoginseng were used as explants, and twelve hormone combinations were tested to induce callus formation. Eight kinds of hormone combinations successfully induced P. notoginseng anther callus. Among these, callus induced by combinations 5 and 7 had the highest saponin content, while those induced by combinations 1 and 3 exhibited the highest relative growth rates. Metabolomic analysis of these four callus types revealed that there were a total of 99 differential metabolites between combinations 5 and 7, 30 between combinations 1 and 3, 123 between combinations 3 and 7, and 116 between combinations 1 and 5. Further analysis showed that the tricarboxylic acid (TCA) cycle metabolites in callus induced by combinations 1 and 3 were significantly upregulated, with corresponding genes showing high expression levels, increased ATP accumulation, and low responses of the auxin response factor PnARF-3 and cytokinin response factor PnCRF-3. The abundance of metabolites in the PNS biosynthesis pathway in callus induced by combinations 5 and 7 increased significantly, with related genes showing high expression levels, increased IPP accumulation, and high responses of PnARF-3 and PnCRF-3. Overexpression of PnARF-3 and PnCRF-3 in callus induced by combination 3 promoted the production of IPP and saponins while reducing ATP production. In conclusion, different hormone combinations affect the distribution of Acetyl-CoA through PnARF-3 and PnCRF-3, resulting in the relative growth rate and saponin of P. notoginseng anther callus differences.

MCTP controls nucleocytoplasmic partitioning of AUXIN RESPONSE FACTORs during lateral root development.

The plant hormone auxin orchestrates almost all aspects of plant growth and development. AUXIN RESPONSE FACTORs (ARFs) control the transcription of auxin-responsive genes, forming cytoplasmic condensates to modulate auxin sensitivity and diversify auxin response regulation. However, the dynamic control of ARF distribution across different subcellular compartments remains largely obscure. Here, we show that three MULTIPLE C2 DOMAIN AND TRANSMEMBRANE REGION PROTEINs (MCTPs), MCTP3, MCTP4, and MCTP6, control ARF nucleocytoplasmic partitioning and determine lateral root development. MCTP3/4/6 are highly expressed in lateral roots and specifically interact with ARF7 and ARF19 to dissolve their cytoplasmic condensates. This promotes ARF nuclear localization in lateral root primordia and enhances auxin signaling during lateral root formation. Our findings confer MCTP as a key switch to modulate auxin responses and outline an MCTP-ARF signaling cascade that is crucial for the establishment of the plant root system.

Endoplasmic reticulum-anchored proteins in control of AUXIN RESPONSE FACTOR condensation.

Sequestration of AUXIN RESPONSE FACTOR (ARF) transcription factors in cytoplasmic condensates represents a specialized mechanism for modulating cellular auxin responsiveness. In this issue of Developmental Cell, Xuan etal. show that MULTIPLE C2-DOMAIN AND TRANSMEMBRANE REGION PROTEIN (MCTP) proteins stimulate lateral root development by antagonizing ARF7 and ARF19 condensation.

Silencing of the MP Gene via dsRNA Affects Root Development and Growth in the Invasive Weed Mikania micrantha.

Mikania micrantha ("mile-a-minute" weed) is a global invasive alien weed that can cause severe damage to agroforestry ecosystems and significant agricultural losses worldwide. Although chemical, manual, or mechanical control methods are widely used to control M. micrantha, RNA interference (RNAi)-based biocontrol methods have rarely been reported for this species. The MONOPTEROS (MP) gene, encoding an auxin response factor, plays an essential role in embryonic root initiation in Arabidopsis thaliana. In this study, we identified the MP gene from M. micrantha via orthologous gene analysis. A total of 37 MP orthologous genes was identified in 4 plants, including 9 MP candidate genes in M. micrantha, 13 in Helianthus annuus, 6 in Chrysanthemum nankingense, and 9 in Lactuca sativa. Phylogenetic analysis revealed that an MP candidate gene in M. micrantha (Mm01G000655, named MmMP) was clustered into one clade with the MP gene in A. thaliana (AtMP). In addition, both MmMP and AtMP contain a B3-DNA binding domain that is shared by transcription factors that regulate plant embryogenesis. To study gene function, dsRNA against MmMP (dsMmMP) was applied to the roots of M. micrantha. Compared with those of the controls, the expression of MmMP was reduced by 43.3%, 22.1%, and 26.2% on the first, third, and fifth days after dsMmMP treatment, respectively. The dsMmMP-treated plants presented several morphological defects, mostly in the roots. Compared with water-treated plants, the dsMmMP-treated plants presented reduced developmental parameters, including root length, number of adventitious roots, root fresh and dry weights, plant height, and aboveground biomass. Additionally, safety assessment suggested that this dsMmMP treatment did not silence MP genes from non-target plants, including rice and tomato; nor did it inhibit root growth in those species. Collectively, these results suggest that MmMP plays an important role in root development in M. micrantha and provides a potential target for the development of species-specific RNAi-based herbicides.

Deciphering the Genetic and Biochemical Drivers of Fruit Cracking in Akebia trifoliata.

This study investigates the molecular mechanisms underlying fruit cracking in Akebia trifoliata, a phenomenon that significantly impacts fruit quality and marketability. Through comprehensive physiological, biochemical, and transcriptomic analyses, we identified key changes in cell wall components and enzymatic activities during fruit ripening. Our results revealed that ventral suture tissues exhibit significantly elevated activities of polygalacturonase (PG) and β-galactosidase compared to dorsoventral line tissues, indicating their crucial roles in cell wall degradation and structural weakening. The cellulose content in VS tissues peaked early and declined during ripening, while DL tissues maintained relatively stable cellulose levels, highlighting the importance of cellulose dynamics in fruit cracking susceptibility. Transcriptomic analysis revealed differentially expressed genes (DEGs) associated with pectin biosynthesis and catabolism, cell wall organization, and oxidoreductase activities, indicating significant transcriptional regulation. Key genes like AKT032945 (pectinesterase) and AKT045678 (polygalacturonase) were identified as crucial for cell wall loosening and pericarp dehiscence. Additionally, expansin-related genes AKT017642, AKT017643, and AKT021517 were expressed during critical stages, promoting cell wall loosening. Genes involved in auxin-activated signaling and oxidoreductase activities, such as AKT022903 (auxin response factor) and AKT054321 (peroxidase), were also differentially expressed, suggesting roles in regulating cell wall rigidity. Moreover, weighted gene co-expression network analysis (WGCNA) identified key gene modules correlated with traits like pectin lyase activity and soluble pectin content, pinpointing potential targets for genetic manipulation. Our findings offer valuable insights into the molecular basis of fruit cracking in A. trifoliata, laying a foundation for breeding programs aimed at developing crack-resistant varieties to enhance fruit quality and commercial viability.

VvFHY3 links auxin and endoplasmic reticulum stress to regulate grape anthocyanin biosynthesis at high temperatures.

Anthocyanins affect quality in fruits such as grape (Vitis vinifera). High temperatures reduce anthocyanin levels by suppressing the expression of anthocyanin biosynthesis genes and decreasing the biosynthetic rate. However, the regulatory mechanisms that coordinate these 2 processes remain largely unknown. In this study, we demonstrate that high-temperature-mediated inhibition of anthocyanin biosynthesis in grape berries depends on the auxin and endoplasmic reticulum (ER) stress pathways. Inactivation of these pathways restores anthocyanin accumulation under high temperatures. We identified and characterized FAR-RED ELONGATED HYPOCOTYL3 (FHY3), a high-temperature-modulated transcription factor that activates multiple anthocyanin biosynthesis genes by binding to their promoters. The auxin response factor VvARF3 interacts with VvFHY3 and represses its transactivation activity, antagonizing VvFHY3-induced anthocyanin biosynthesis. Additionally, we found that the ER stress sensor VvbZIP17 represses anthocyanin biosynthesis. VvFHY3 suppresses VvbZIP17 activity by directly binding to the VvbZIP17 promoter to repress its transcription and by physically interacting with VvbZIP17 to block its DNA binding ability. Furthermore, AUXIN RESPONSE FACTOR 3 (ARF3) interferes with the VvFHY3-VvbZIP17 interaction, releasing VvbZIP17 to activate the unfolded protein response and further suppress anthocyanin production. Our results unravel the VvARF3-VvFHY3-VvbZIP17 regulatory module, which links the auxin and ER stress pathways to coordinately repress anthocyanin structural gene expression and biosynthesis under high-temperature stress.

Exploring Genomic Regions Associated with Fruit Traits in Pepper: Insights from Multiple GWAS Models.

This study utilized 303 pepper accessions from diverse Capsicum species to explore fruit traits, including length, width, wall thickness, and weight. Descriptive statistics revealed a mean fruit length of 66.19 mm, width of 23.48 mm, wall thickness of 1.89 mm, and weight of 15.29 g, with significant variability, particularly in fruit weight. Correlation analysis demonstrated strong positive relationships between fruit width, weight, and fruit wall thickness (r = 0.89 and r = 0.86, respectively), while fruit length showed weaker correlations with these traits. Analysis of fruit positions revealed that the majority of accessions had a pendent fruit position (156), followed by erect (85) and intermediate (8). In terms of fruit shape, triangular and narrow triangular shapes were the most common, observed in 102 and 98 accessions, respectively. Genome-wide association studies (GWAS) identified significant single nucleotide polymorphisms (SNPs) associated with fruit traits across four models (Blink, FarmCPU, MLM, MLMM). The number of significantly associated SNPs were as follows: fruit length (89), fruit width (55), fruit weight (63), fruit wall thickness (48), fruit shape (151), and fruit position (51). Several genes were also identified where the SNPs are located or adjacent to, providing candidate genes for further exploration of the genetic basis of fruit morphology. Notably, genes such as E3 ubiquitin-protein ligase RGLG1 (associated with fruit width), Homeobox-leucine zipper protein HDG11 (involved in fruit width), Auxin response factor 23 (linked to fruit shape), and ATP-dependent zinc metalloprotease FtsH (related to fruit weight) were identified. These findings enhance our understanding of the genetic basis of fruit morphology in Capsicum, offering valuable insights for breeding and agricultural practices.

Fast and simple fluorometric measurement of phloem loading exposes auxin-dependent regulation of Arabidopsis sucrose transporter AtSUC2.

The rate of sucrose export from leaves is a major factor in balancing whole-plant carbon and energy partitioning. A comprehensive study of its dynamics and relationship to photosynthesis, sink demand, and other relevant processes is hampered by the shortcomings of current methods for measuring sucrose phloem loading. We utilize the ability of sucrose transporter proteins, known as SUCs or SUTs, to specifically transport the fluorescent molecule esculin in a novel assay to measure phloem loading rates. Esculin was administered to source leaves and its fluorescence in the leaf extract was measured after 1 or 2 h. Dicot plants with an active phloem loading strategy showed an export-dependent reduction of esculin fluorescence. Relative leaf esculin export rates correlated with leaf export rates of isotopic carbon and phloem exudate sucrose levels. We used esculin experiments to examine the effects of phytohormones on phloem loading in Arabidopsis, showing, for example, that auxin induces phloem loading while cytokinin reduces it. Transcriptional regulation of AtSUC2 by AUXIN RESPONSE FACTOR1 (ARF1) corroborated the link between auxin signaling and phloem loading. Unlike established methods, the esculin assay is rapid and does not require specialized equipment. Potential applications and limitations of the esculin assay are discussed.

A mobile miR160-triggered transcriptional axis controls root stem cell niche maintenance and regeneration in Arabidopsis.

In multicellular organisms, communication between cells is vital for their fate determination. In plants, the quiescent center (QC) signals to adjacent stem cells to maintain them undifferentiated. However, how surrounding stem cells instruct the QC remains poorly understood. Here, we show that in the Arabidopsis root, microRNA160 (miR160) moves from stele stem cells (SSCs) to the QC, where it degrades the mRNAs of two auxin response factors, ARF10 and ARF17. This degradation relieves BRAVO from direct transcriptional repression, maintaining QC quiescence. We further identify that blocking miR160 movement due to DNA damage-induced SSC death and restricted symplastic transport reduces BRAVO and WOX5 expression, leading to QC division to replenish damaged stem cells during root regeneration. Together, our results demonstrate that a transcriptional axis initiated by mobile miR160 regulates the QC and stem cell behavior, advancing our understanding of the communication between stem cells and their surrounding cellular environment.

The OsMAPK5-OsWRKY72 module negatively regulates grain length and grain weight in rice.

Grain size and grain weight are important determinants for grain yield. In this study, we identify a novel OsMAPK5-OsWRKY72 module that negatively regulates grain length and grain weight in rice. We found that loss-of-function of OsMAPK5 leads to larger cell size of the rice spikelet hulls and a significant increase in both grain length and grain weight in an indica variety Minghui 86 (MH86). OsMAPK5 interacts with OsMAPKK3/4/5 and OsWRKY72 and phosphorylates OsWRKY72 at T86 and S88. Similar to the osmapk5 MH86 mutants, the oswrky72 knockout MH86 mutants exhibited larger size of spikelet hull cells and increased grain length and grain weight, whereas the OsWRKY72-overexpression MH86 plants showed opposite phenotypes. OsWRKY72 targets the W-box motifs in the promoter of OsARF6, an auxin response factor involved in auxin signaling. Dual-luciferase reporter assays demonstrated that OsWRKY72 activates OsARF6 expression. The activation effect of the phosphorylation-mimicking OsWRKY72T86D/S88D on OsARF6 expression was significantly enhanced, whereas the effects of the OsWRKY72 phosphorylation-null mutants were significantly reduced. In addition, auxin levels in young panicles of the osmapk5 and oswrky72 mutants were significantly higher than that in the wild-type MH86. Collectively, our study uncovered novel connections of the OsMAPKK3/4/5-OsMAPK5-mediated MAPK signaling, OsWRKY72-mediated transcription regulation, and OsARF6-mediated auxin signaling pathways in regulating grain length and grain weight in an indica-type rice, providing promising targets for molecular breeding of rice varieties with high yield and quality.

Plant hormone signaling is involved in regulating flower bud size of daylily

To explore the role and metabolic differences of plant hormones in regulating the flower bud size of daylily, we collected the flower buds from two daylily varieties 'Datong Huanghua' and 'Dongbei Huanghua' at the young bud, green, yellowing, and yellow stages for transcriptome sequencing. The differentially expressed genes (DEGs) were screened, and the exogenous plant hormone spraying experiments were conducted. A total of 199 DEGs related to the biosynthesis and metabolism of plant hormones was screened out at different flower development stages of 'Datong Huanghua' and 'Dongbei Huanghua'. These genes regulated the biosynthesis and metabolism of six plant hormones: abscisic acid, gibberellin, auxin, jasmonate, cytokinin, and ethylene. The DEGs associated with auxin were the most, which suggested that auxin played a role in regulating flower bud development. The auxin response factor (ARF) presented up-regulated expression at all the four stages of flower bud development, indicating that ARF played a positive regulatory role throughout the flower bud development of daylily. The experiments with exogenous spraying of six hormones further verified that indole-3-acetic acid (IAA) significantly promoted the growth and increased the nutrient content in the flower buds of 'Datong Huanghua', suggesting that IAA played a role in regulating flower bud development. Our results laid a theoretical foundation for probing into the regulatory mechanism of flower bud development of 'Datong Huanghua' and 'Dongbei Huanghua'.

Tomato SlARF5 participate in the flower organ initiation process and control plant height

Plant height is a critical agronomic trait closely linked to yield, primarily regulated by Gibberellins (GA) and auxins, which interact in complex ways. However, the mechanism underlying their interactions remain incompletely understood. In this study, we identified a tomato mutant exhibiting significantly reduced plant height. Through gene cloning and bulked segregant analysis (BSA) sequencing, we found that the mutant gene corresponds to the tomato auxin response factor gene SlARF5/MP. Here, we show that overexpression of SlARF5/MP significantly enhances plant height. Additionally, treatment with GA3 restored the plant height of the mutant to wild-type (WT) levels, indicating that GA content is a key factor influencing plant height. We also observed significant upregulation of GA-biosynthesis genes, including GA2-oxidases GA20ox3 and GA20ox4, as well as the GA3 biosynthesis gene GA3ox1, in SlARF5-overexpressing plants. Furthermore, we demonstrated that SlARF5 directly binds to SlGA2ox3, which mediates the conversion of GA3 to inactive GA, therebyregulating its expression. Our findings suggest that SlARF5 modulates GA3 metabolism by regulating GA synthesis genes, ultimately leading to alterations in plant height.

GhGRF4/GhARF2-GhGASA24 module regulates fiber cell wall thickness by modulating cellulose biosynthesis in upland cotton (Gossypium hirsutum).

Fiber elongation rate is an essential characteristic of cotton fiber in the textile industry, yet it has been largely overlooked in genetic studies. Gibberellins (GAs) and auxin (IAA) are recognized for their role in directing numerous developmental processes in plants by influencing cell differentiation and elongation. However, the degree to which GA-IAA interaction governs cellular elongation in cotton fiber cells remains to be fully understood. In this study, we identified a causal gene, Gibberellic Acid-Stimulated in Arabidopsis 24 (GhGASA24), that appears to be responsible for fiber elongation rate via regulating fiber cell wall thickness. Subsequent experiments revealed that GhGASA24 influences cell wall formation by promoting the expression of GhCesA8 and GhCesA10. Our findings suggest that Auxin Response Factor 2 (GhARF2) regulates fiber elongation rate by directly binding to the AuxRE elements in GhGASA24 promoter. In addition, we identified Growth Regulation Factor 4 (GhGRF4) as a transcription factor that interacts with GhARF2 to form a heterodimer complex, which also transcriptionally activates GhGASA24. Intriguingly, GhGRF4 regulates GhARF2 expression by directly binding to its promoter, thereby acting as a cascade regulator to enhance the transcriptional levels of GhGASA24. We propose that the GhGRF4/GhARF2-GhGASA24-GhCesAs module may contribute to fiber cell wall thickness by modulating cellulose biosynthesis, and provide a theoretical basis for improvement of fiber quality.

Pseudomonas chlororaphis subsp. aurantiaca Stimulates Lateral Root Development by Integrating Auxin and Reactive Oxygen Species Signaling in Arabidopsis.

Plant growth-promoting rhizobacteria (PGPR) can promote lateral root formation, while the underlying mechanisms are not fully understood. Here, we found that Pseudomonas chlororaphis subsp. aurantiaca inoculation enhanced auxin accumulation in lateral root primordia (LRP). Upon reaching LRPs, auxin activated the AUXIN RESPONSE FACTOR 7 and 19 (ARF7/19) and promoted lateral root formation in Arabidopsis. Moreover, we found that reactive oxygen species (ROS) is required for auxin-dependent lateral root emergence, and P. chlororaphis upregulated the expression of RESPIRATORY BURST OXIDASE D and F (RBOHD/F), leading to the accumulation of ROS in LRP. Although scavenging ROS or rbohd/f mutants exhibited decreased lateral roots after P. chlororaphis inoculation, the bacteria-triggered auxin signals were not altered. Conversely, the application of auxin or mutants defective in auxin signaling disturbed P. chlororaphis-derived ROS accumulation in lateral roots. Collectively, these results suggest that ARF7/19-dependent auxin signaling activates RBOHD/F to produce ROS, coordinately facilitating lateral root development after P. chlororaphis treatment.