Exogenous Application Of Auxin Research Articles

Re-harvest application of 2-(3-chlorophenoxy) propionic acid on pineapple plants

The application of plant regulators such as exogenous auxin may provide effects on the translocation of carbohydrates to plant sinks, which may result in larger parthenocarpic fruits. The objective of the study was to evaluate the effects of the application of 2-(3-chlorophenoxy) propionic acid on the growth and quality of pineapple fruits. The experiment was carried out in a randomized block design. After floral induction, 2-(3-chlorophenoxy) propionic acid (CPA) was applied directly on the inflorescences at the following doses: 0 mg L-1; 40.0 mg L-1; 80.0 mg L-1; 120.0 mg L-1 and 160.0 mg L-1. Growth evaluations continued until 84 days after application, measuring fruit length (cm) with and without crown, crown length (cm), leaf D dry matter, fruit weight with and without crown (g), calculating if also, the absolute and relative growth rates. The post-harvest and quality characteristics of the fruits were also evaluated, as well as the harvest index. The application of CPA significantly reduces the length and weight of the crown of the fruits, however, the exogenous application of auxin provided an increase in the weight of the fruit. Regarding the post-harvest analysis, the application of CPA reduced the content of soluble solids in the fruit pulp.

Insights into the molecular basis of beet curly top resistance in sugar beet through a transcriptomic approach at the early stage of symptom development

Curly top disease caused by Beet curly top virus (BCTV) is a limiting factor for sugar beet production. The most economical and sustainable control of BCTV in sugar beet would be via the growth of resistant cultivars, although most commercial cultivars possess only low-to-moderate quantitative resistance. A double haploid line (KDH13) showed a high level of resistance to BCTV infection. However, the mechanism of resistance and response of this line to BCTV infection is unknown. Here, we tested the response of this line to both local and systemic BCTV infections. The virus replicated at a high level in locally infected tissue but lower than in susceptible KDH19 plants. Resistant KDH13 plants systemically infected with BCTV showed only mild enation without leaf curling after 30 days. In contrast, severe leaf curling appeared after 12 days in susceptible plants with higher virus accumulation. Transcriptome analysis of the BCTV-infected KDH13 plants at the early stage of symptom development showed only 132 genes that were exclusively deregulated compared to the regulation of a large number of genes (1018 genes) in KDH19 plants. Pathway enrichment analysis showed that differentially expressed genes were predominantly involved in hormone metabolism, DNA methylation, immune response, cell cycle, biotic stress and oxidative stress. The auxin level in both resistant and susceptible plants increased in response to BCTV infection. Remarkably, exogenous application of auxin caused leaf curling phenotype in the absence of the virus. This study demonstrates the response of resistant and susceptible plants to BCTV infection at both local and systemic infections and highlights the defence-related genes and metabolic pathways including auxin for their contribution towards BCTV symptom development and resistance in sugar beet.

Impact of Various IBA Concentrations on Rooting in Apical Shoot Cutting and Stem Cuttings of Callistemon lanceolatus (Sm.) Sweet in Polytunnel Conditions

The study was undertaken to identify the optimal concentration of IBA and type of cuttings suitable for propagation of Callistemon lanceolatus and it was conducted at the Vanavarayar Institute of Agriculture, Pollachi, Coimbatore, India from December 2022 to September 2023. The experiment addressed the challenges of seed propagation, such as their seed capsules need to be activated by fire and the unpredictable nature of seed germination, which results in high progeny diversity due to genetic recombination. The investigation focused on apical and stem cuttings subjected to fifteen different treatments with three replications each; the Tukey test was used for statistical analysis; the cuttings were treated with various concentrations of Indole-3-butyric acid (IBA) and placed under polytunnel conditions; observations were made after 45 days, measuring sprouting percentage, rooting percentage, mean number of leaves, shoot length, mean number of roots, and root length per cutting. In light of these issues, the study explored clonal propagation as an alternative for mass multiplication of elite trees. The results of the study depicted that the maximum rooting percentage and root length were observed in T6 (73.28±8.87%) and (12.54±0.00cm) due to the exogenous application of auxin. On the whole, the result of this investigation suggest that apical shoot cuttings with IBA at 6000ppm can be made to induce maximum rooting and to produce high quality planting stock material for clonal propagation in Callistemon lanceolatus.

Comparative transcriptome and functional analyses provide insights into the key factors regulating shoot regeneration in highbush blueberry.

Establishing an efficient plant regeneration system is a crucial prerequisite for genetic engineering technology in plants. However, the regeneration rate exhibits considerable variability among genotypes, and the key factors underlying shoot regeneration capacity remain largely elusive. Blueberry leaf explants cultured on a medium rich in cytokinins exhibit direct shoot organogenesis without prominent callus formation, which holds promise for expediting genetic transformation while minimizing somatic mutations during culture. The objective of this study is to unravel the molecular and genetic determinants that govern cultivar-specific shoot regeneration potential in highbush blueberry (Vaccinium corymbosum L.). We conducted comparative transcriptome analysis using two highbush blueberry genotypes: 'Blue Muffin' ('BM') displaying a high regeneration rate (>80%) and 'O'Neal' ('ON') exhibiting a low regeneration rate (<10%). The findings revealed differential expression of numerous auxin-related genes; notably, 'BM' exhibited higher expression of auxin signaling genes compared to 'ON'. Among blueberry orthologs of transcription factors involved in meristem formation in Arabidopsis, expression of VcENHANCER OF SHOOT REGENERATION (VcESR), VcWUSCHEL (VcWUS), and VcCUP-SHAPED COTYLEDON 2.1 were significantly higher in 'BM' relative to 'ON'. Exogenous application of auxin promoted regeneration, as well as VcESR and VcWUS expression, whereas inhibition of auxin biosynthesis yielded the opposite effects. Overexpression of VcESR in 'BM' promoted shoot regeneration under phytohormone-free conditions by activating the expression of cytokinin- and auxin-related genes. These findings provide new insights into the molecular mechanisms underlying blueberry regeneration and have practical implications for enhancing plant regeneration and transformation techniques.

Response of Dragon Fruit (Hylocereus sp.) Cuttings to Different Plant Growth Regulators.

Dragon fruit (Hylocereus sp.) is an exotic crop with a great potential for its cultivation in semi arid tracts throughout India. Its planting is mainly confined to harsh climates and degraded lands facing challenges in its establishment. Hence, availability of quality planting material is essential for attaining success. Due to long juvenile phase of the sexually propagated seedlings it can be propagated asexually by stem cuttings but proper rooting is not possible without exogenous auxin application. Hence, during 2022-2023 a research was carried out at the Horticultural Experimental area of Khalsa College, Amritsar to standardize the concentration of plant growth regulators viz. IBA, NAA and PHB for rooting and success rate in stem cuttings comprising of sixteen treatments with three replications arranged in randomized block design. The results revealed that the stem cuttings treated with IBA 4000 ppm proved to be superior for the sprouting and survival of the cuttings resulting in the improved vegetative growth with profuse, longer, thicker and the heaviest roots. Hence, the cutting treatment of IBA 4000 ppm can be proposed for dragon fruit plant propagation to meet the market demand in India.

Biomass ash as soil fertilizers: Supercharging biomass accumulation by shifting auxin distribution

Growing quantities of biomass ashes (phyto-ashs) are currently produced worldwide due to the increasing biomass consumption in energy applications. Utilization of phyto-ash in agriculture is environmentally friendly solution. However, mechanisms involving the coordination of carbon metabolism and distribution in plants and soil amendment are not well known. In the present study, tobacco plants were chemically-fertilized with or without 2‰ phyto-ash addition. The control had sole chemical fertilizer; for two phyto-ash treatments, the one (T1) received comparable levels of nitrogen, phophorus, and potassium from phyto-ash and fertilizers as the control and another (T2) had 2‰ of phyto-ash and the same rates of fertilizers as the control. Compared with the control, phyto-ash addition improved the soil pH from 5.94 to about 6.35; T2 treatment enhanced soil available potassium by 30% but no difference of other elements was recorded among three treatments. Importantly, bacterial (but not fungal) communities were significantly enriched by phyto-ash addition, with the rank of richness as: T2 > T1 > control. Consistent with amelioration of soil properties, phyto-ash promoted plant growth through enlarged leaf area and photosynthesis and induced outgrowth of lateral roots (LRs). Interestingly, increased auxin content was recorded in 2nd and 3rd leaves and roots under phyto-ash application, also with the rank level as T2 > T1 > control, paralleling with higher transcripts of auxin synthetic genes in the topmost leaf and stronger [3H]IAA activity under phyto-ash addition. Furthermore, exogenous application of analog exogenous auxin (NAA) restored leaf area, photosynthesis and LR outgrowth to the similar level as T2 treatment; conversely, application of auxin transport inhibitor (NPA) under T2 treatment retarded leaf and root development. We demonstrated that phyto-ash addition improved soil properties and thus facilitated carbon balance within plants and biomass accumulation in which shifting auxin distribution plays an important role.

Ethylene regulates auxin-mediated root gravitropic machinery and controls root angle in cereal crops.

Root angle is a critical factor in optimising the acquisition of essential resources from different soil depths. The regulation of root angle relies on the auxin-mediated root gravitropism machinery. While the influence of ethylene on auxin levels is known, its specific role in governing root gravitropism and angle remains uncertain, particularly when Arabidopsis (Arabidopsis thaliana) core ethylene signaling mutants show no gravitropic defects. Our research, focusing on rice (Oryza sativa L.) and maize (Zea mays), clearly reveals the involvement of ethylene in root angle regulation in cereal crops through the modulation of auxin biosynthesis and the root gravitropism machinery. We elucidated the molecular components by which ethylene exerts its regulatory effect on auxin biosynthesis to control root gravitropism machinery. The ethylene-insensitive mutants ethylene insensitive2 (osein2) and ethylene insensitive like1 (oseil1), exhibited substantially shallower crown root angle compared to the wild type. Gravitropism assays revealed reduced root gravitropic response in these mutants. Hormone profiling analysis confirmed decreased auxin levels in the root tips of the osein2 mutant, and exogenous auxin (NAA) application rescued root gravitropism in both ethylene-insensitive mutants. Additionally, the auxin-biosynthetic mutant mao hu zi10 (mhz10)/tryptophan aminotransferase2 (ostar2) showed impaired gravitropic response and shallow crown root angle phenotypes. Similarly, maize ethylene-insensitive mutants (zmein2) exhibited defective gravitropism and root angle phenotypes. In conclusion, our study highlights that ethylene controls the auxin-dependent root gravitropism machinery to regulate root angle in rice and maize, revealing a functional divergence in ethylene signaling between Arabidopsis and cereal crops. These findings contribute to a better understanding of root angle regulation and have implications for improving resource acquisition in agricultural systems.

A Comprehensive Analysis of Transcriptomics and Metabolomics Revealed Key Pathways Involved in Saccharum spontaneum Defense against Sporisorium scitamineum.

Sugarcane smut, caused by Sporisorium scitamineum, poses a severe threat to sugarcane production. The genetic basis of sugarcane resistance to S. scitamineum remains elusive. A comparative transcriptomic and metabolomic study was conducted on two wild Saccharum species of S. spontaneum with contrast smut resistance. Following infection, the resistant line exhibited greater down-regulation of genes and metabolites compared to the susceptible line, indicating distinct biological processes. Lignan and lignin biosynthesis and SA signal transduction were activated in the resistant line, while flavonoid biosynthesis and auxin signal transduction were enhanced in the susceptible line. TGA2.2 and ARF14 were identified as playing positive and negative roles, respectively, in plant defense. Exogenous auxin application significantly increased the susceptibility of S. spontaneum to S. scitaminum. This study established the significant switching of defense signaling pathways in contrast-resistant S. spontaneum following S. scitamineum infection, offering a hypothetical model and candidate genes for further research into sugarcane smut disease.

A Useful Pathway for Gnetum Planting Material Production: Effect of Exogenous Application of Auxin on Root and Shoot Expression of Gnetum Cuttings

A Useful Pathway for Gnetum Planting Material Production: Effect of Exogenous Application of Auxin on Root and Shoot Expression of Gnetum Cuttings

The effects of heat stress on male reproduction and tillering in Sorghum bicolor

AbstractDue to global climate change, heat stress is increasingly harming the growth, development, overall biomass, and grain yield of numerous crops. Heat stress impairs pollen development and thus reduces seed set in Sorghum bicolor (L.) Moench; however, the effects of heat stress on anther development at specific stages and tiller formation remain incompletely understood. Here we report that exposure to heat stress [42°C/32°C (day/night)] at pollen mother cell (PMC) and booting stages profoundly disrupts tapetum and pollen development, resulting in a significant decrease in grain yield in sorghum. Sorghum plants subjected to 9 days or less of heat stress at the PMC stage exhibited normal pollen viability, but 12 days of heat stress caused almost complete loss of grain yield and the formation of nonviable pollen grains. Similarly, sorghum plants that were heat‐stressed for 3 days at the booting stage produced few seeds. Further analysis revealed that aberrant tapetum and pollen development contributed to the sterility of pollen in these heat‐stressed plants. Notably, in addition to inhibiting plant height, a 12‐day heat stress at the PMC stage promoted the formation of basal tillers, whereas a 3‐day heat stress at the booting stage stimulated the formation of apical tillers, which helped salvage seed yield under heat stress conditions. Moreover, the application of exogenous auxin promoted the formation of apical tillers and leaf numbers per apical tiller. Collectively, our findings suggest that sorghum is susceptible to heat stress during both early and late anther development, and auxin might be involved in governing the formation of apical tillers.

Insight into regulation of adventitious root formation by arbuscular mycorrhizal fungus and exogenous auxin in tea plant (Camellia sinensis L.) cuttings.

Adventitious root (AR) development, affected by various biotic and abiotic factors, is the most important procedure in tea plant (Camellia sinensis L.) cutting propagation. Establishing symbiotic relationships with most terrestrial plants, AMF (Arbuscular mycorrhizal fungus) can mediate the AR formation of several herbaceous and woody plants in previous studies. In this paper, effects of combined application of AMF and exogenous auxin on AR formation of cuttings from different tea plant varieties ('Pingyangtezao', 'Longjing 43' and 'Longjingchangye') were studied. Then we also performed RNA-Seq analysis with 'Pingyangtezao' cuttings aiming to find the possible auxin-related pathway of AM fungal regulation on AR formation. To accurately uncover the regulatory mechanism of AMF on AR formation of tea cuttings, rooting process were separated into four stages (S0, non-rooting; S1, AR protrusion; S2, AR formation and S3, AR elongation) at the same sampling time. Results showed that IBA treatment increased the mycorrhizal colonization rate, especially in 'Pingyangtezao' variety (from 37.58% to 46.29%). Both inoculating AMF and addition of IBA promoted the AR formation, and rooting of different tea plant varieties showed different dependence on auxin. AMF could alleviate the effect of auxin-related inhibitors (2,3,5-triiodobenzoic acid, L-α-(Aminooxy)-β-phenylpropionic acid and α-(phenylethyl-2-oxo)-IAA) on rooting of tea cuttings, even though the colonization of AMF was hindered at various degrees. Transcriptomic analysis showed that different numbers of differentially expressed genes (DEGs) at various rooting stages of tea cuttings with the most at S2 stage (1360 DEGs), indicating the increasing regulation by AMF with the development of AR. Similar trend was found in auxin-related DEGs, and family genes of YUC, GH, PIN, LAX, SAUR, AUX, and ABP involved in the AM fungal regulation on AR formation of tea cuttings. Additionally, AMF strongly mediated auxin transport and signal transduction pathways in tea cuttings as showed by the results of correlation analysis. Overall, interaction of AMF and exogenous auxin in promoting rooting and the preliminary mechanism of AMF regulating AR formation of tea cuttings was deciphered in this paper, which may provide a basis for further deep mechanistic research and cutting propagation of tea production.

Spatially activated conserved auxin-transcription factor regulatory module controls de novo root organogenesis in rice.

This study reveals that the process of crown root development and auxin-induced de novo root organogenesis during in vitro plantlet regeneration share a common auxin-OsWOX10 regulatory module in rice. In the fibrous-type root system of rice, the crown roots (CR) are developed naturally from the shoot tissues. Generation of robust auxin response, followed by activation of downstream cell fate determinants and signaling pathways at the onset of crown root primordia (CRP) establishment is essential for new root initiation. During rice tissue culture, embryonic calli are induced to regenerate shoots in vitro which undergo de novo root organogenesis on an exogenous auxin-supplemented medium, but the mechanism underlying spatially restricted root organogenesis remains unknown. Here, we reveal the dynamics of progressive activation of genes involved in auxin homeostasis and signaling during initiation and outgrowth of rice crown root primordia. By comparative global dataset analysis, we identify the crown root primordia-expressed genes whose expression is also regulated by auxin signaling. In-depth spatio-temporal expression pattern analysis shows that the exogenous application of auxin induces a set of key transcription factors exclusively in the spatially positioned CRP. Further, functional analysis of rice WUSCHEL-RELATED HOMEOBOX 10 (OsWOX10) during in vitro plantlet regeneration from embryogenic calli shows that it promotes de novo root organogenesis from regenerated shoots. Expression of rice OsWOX10 also induces adventitious roots (AR) in Arabidopsis, independent of homologous endogenous Arabidopsis genes. Together, our findings reveal that a common auxin-transcription factor regulatory module is involved in root organogenesis under different conditions.

Exogenous application of synthetic auxin (2,4-dichlorophenoxyacetic acid) impacts on growth, yield, and nutritional parameters of lentil (Lens culinaris M.)

An experiment was conducted to evaluate the impacts of exogenous application of synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) on lentil (Lens culinaris M.) growth, yield, and nutritional parameters in the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh. Six treatments of 2,4-D (T0 = 0; T1 = 0.3; T2 = 0.5; T3 = 0.8; T4 = 1; and T5 = 1.2 ppm 2,4-D) with three replications were used in this study. Data on growth, yield, and nutritional parameters were collected and analyzed. The response of exogenous application of 2,4-D was significant in improving the performance of all the growth and yield contributing parameters as compared to untreated control plants. Exogenous application of 1 ppm 2,4-D was found to be effective for increasing plant height, branch number, root length, root-shoot fresh, and dry weight, nodule number, flower number, pod number, pod length, number of grains plant-1, 100-grain weight, and yield. Exogenous 2,4-D treatment significantly reduced the maturity time of lentil grain. The lowest date of maturity was found at 0.8, 1.0, and 1.2 ppm 2,4-D treatments. In this study, results showed a significant increase of different macro- (N, P, K) and micro- (Fe, Mn, Zn) nutrient content, uptake, and protein content in lentil grains with 1 ppm 2,4-D. It has been also revealed that the minimum requirement of 2,4-D to produce 80% lentil yield was 0.83 ppm. As a result, it was determined that the exogenous application of 2,4-D treatments is promising for enhancing the growth and productivity of lentil.

The changes in the maize root cell walls after exogenous application of auxin in the presence of cadmium.

Cadmium (Cd) is a transition metal and hazardous pollutant that has many toxic effects on plants. This heavy metal poses a health risk for both humans and animals. The cell wall is the first structure of a plant cell that is in contact with Cd; therefore, it can change its composition and/or ratio of wall components accordingly. This paper investigates the changes in the anatomy and cell wall architecture of maize (Zea mays L.) roots grown for 10 days in the presence of auxin indole-3-butyric acid (IBA) and Cd. The application of IBA in the concentration 10-9 M delayed the development of apoplastic barriers, decreased the content of lignin in the cell wall, increased the content of Ca2+ and phenols, and influenced the composition of monosaccharides in polysaccharide fractions when compared to the Cd treatment. Application of IBA improved the Cd2+ fixation to the cell wall and increased the endogenous concentration of auxin depleted by Cd treatment. The proposed scheme from obtained results may explain the possible mechanisms of the exogenously applied IBA and its effects on the changes in the binding of Cd2+ within the cell wall, and on the stimulation of growth that resulted in the amelioration of Cd stress.

The mRNA decapping machinery targets LBD3/ASL9 to mediate apical hook and lateral root development.

Multicellular organisms perceive and transduce multiple cues to optimize development. Key transcription factors drive developmental changes, but RNA processing also contributes to tissue development. Here, we report that multiple decapping deficient mutants share developmental defects in apical hook, primary and lateral root growth. More specifically, LATERAL ORGAN BOUNDARIES DOMAIN 3 (LBD3)/ASYMMETRIC LEAVES 2-LIKE 9 (ASL9) transcripts accumulate in decapping deficient plants and can be found in complexes with decapping components. Accumulation of ASL9 inhibits apical hook and lateral root formation. Interestingly, exogenous auxin application restores lateral roots formation in both ASL9 over-expressors and mRNA decay-deficient mutants. Likewise, mutations in the cytokinin transcription factors type-B ARABIDOPSIS RESPONSE REGULATORS (B-ARRs) ARR10 and ARR12 restore the developmental defects caused by over-accumulation of capped ASL9 transcript upon ASL9 overexpression. Most importantly, loss-of-function of asl9 partially restores apical hook and lateral root formation in both dcp5-1 and pat triple decapping deficient mutants. Thus, the mRNA decay machinery directly targets ASL9 transcripts for decay, possibly to interfere with cytokinin/auxin responses, during development.

A stratagem for primary root elongation under moderate salt stress in the halophyte Schrenkiella parvula.

Schrenkiella parvula, an Arabidopsis-related halophyte, grows around Lake Tuz (Salt) in Turkey and can survive up to 600 mM NaCl. Here, we performed physiological studies on the roots of S. parvula and A. thaliana seedlings cultivated under a moderate salt condition (100 mM NaCl). Interestingly, S. parvula germinated and grew at 100 mM NaCl, but germination did not occur at salt concentrations above 200 mM. In addition, primary roots elongated much faster at 100 mM NaCl, while being thinner with fewer roots hair, than under NaCl-free conditions. Salt-induced root elongation was due to epidermal cell elongation, but meristem size and meristematic DNA replication were reduced. The expression of genes related to auxin response and biosynthesis was also reduced. Application of exogenous auxin abolished the changes in primary root elongation, suggesting that auxin reduction is the main trigger for root architectural changes in response to moderate salinity in S. parvula. In A. thaliana seeds, germination was maintained up to 200 mM NaCl, but post-germination root elongation was significantly inhibited. Furthermore, primary roots did not promote elongation even under fairly low salt conditions. Compared to A. thaliana, cell death and ROS content in primary roots of salt-stressed plants were significantly lower in S. parvula. These changes in the roots of S. parvula seedlings may be an adaptive strategy to reach lower salinity by advancing into deeper soils, while being impaired by moderate salt stress. This article is protected by copyright. All rights reserved.

The cellulose–lignin balance mediated by auxin signal transduction affects the twisted growth of Yunnan pine trunk

Trunk twisting, a special phenomenon observed during plant growth, leads to remarkable changes in plant phenotypic plasticity and adaptability. However, it is a debate whether the trunk twisting belongs to environmental alteration or genetic variation. To understand the mechanisms underlying trunk twisting in Yunnan pine (Pinus yunnanensis Franch.), through a diallel cross experiment, we first determined that trunk twisting was controlled by recessive genes. Anatomical analysis identified that straight and twisty types differed significantly in xylem and phloem. RNA-seq of materials enriched by laser microdissection revealed several metabolic pathways with significant enrichment in twisty pines, including auxin signal transduction, photosynthetic carbon fixation and sucrose metabolism, etc. Application of exogenous auxin and auxin transport inhibitors (TIBA) can only change the growth rate, but cannot change the twisted or straight of the trunk. When auxin signaling inhibitors (auxinole) were added, the straight pines produce a tendency to twisty growth. Combined with enzyme activity assay and immunohistochemistry, we propose a working model. ARF can not only downregulate POR to block chlorophyll synthesis and photosynthesis but also upregulated Susy expression, and allows a large amount of sucrose to synthesize cellulose. Nevertheless, due to downregulated CBH expression and abnormal cellulolysis, cellulose accumulates and the lignin content decreases, eventually making the trunk highly prone to twisted growth. These results reveal the molecular mechanism of trunk twisting, and suggest that ARF expression method can be vital in trunk shape screening during the early growth stages of Yunnan pines.

Auxin Application at the Flowering Stage of Rice Alleviates the Negative Impact of Heat Stress on Spikelet Fertility and Yield Attributes

The reproductive stage of rice is vulnerable to heat stress, which reduces spikelet fertility and yield. Auxin significantly influences reproductive development, hence the research aimed to enhance spikelet fertility and grain attributes in rice plants by exploring the application efficiency of Indole-3-acetic acid (IAA) and 1-naphthaleneacetic acid (NAA) under heat stress. This study investigated the effects of IAA (10 μmol L−1) and NAA (100 μmol L−1) on spikelet fertility rate in six rice genotypes during the flowering stage. Compared to the heat stress (HS) treatment, the spikelet production rate and grain yield per plant were higher by 61.16%, 37.25%, and 33.07%, and 72.84%, 44.48%, and 32.71% in control, HS + NAA, and HS + IAA treatments, respectively. In addition, panicle weight, primary branches number panicle−1, and 1000-grains weight were significantly (p &lt; 0.05) improved with HS + IAA and HS + NAA application under heat stress conditions. Auxin application enhanced photosynthetic and transpiration rate, while contrarily, leaf temperature diminished. The higher photosynthetic rate showed positive relationships with spikelet fertility (r = 0.64) and yield plant−1 (r = 0.63). Additionally, leaf temperature had a strongly negative correlation (r = −0.81) with the spikelet fertility rate. The application of auxin increased the number of filled grains panicle−1, which showed a positive relationship (r = 0.75) with grain yield plant−1. The variation of spikelet fertility rate among genotypes was dependent on the variety tolerance rate. Overall, these findings indicate that exogenous auxin application can mitigate the negative impact of heat stress on rice and improve spikelet fertility and grain yield.

Analysis of the effect of exogenous auxin on the regulatory relationship between miRNAs and their target genes in rose using high-throughput sequencing

ABSTRACT Rose (Rosa hybrida L.) is one of the major cut flowers in the world. Studying the molecular mechanism of auxin regulation in growth is of great significance for enhancing the understanding of the growth and development processes in rose and informing accurate exogenous auxin application in rose production. However, the response mechanism of rose to miRNA-mediated auxin signal transduction is unclear. In this study, rose plants were treated with IAA, and 75 known miRNAs and 168 novel miRNAs were identified by small RNA sequencing. Among them, 19 known miRNAs and 42 miRNAs were differentially expressed. Many differential miRNAs demonstrated staged responses to auxin treatment. The targeted relationship between miRNA and key transcription factors regulated by auxin in rose was analysed, and the target genes in the ARF family and AUX/IAA family were screened. By using quantitative real-time PCR(qRT-PCR) to verify the expression patterns of the miRNA regulating the auxin signal transduction pathway and its target gene, we found that miR156a, miR160a, miR164a, miR167d, miR396b-3p, novel_miR_189, novel_miR_74, novel_miR_8, and novel_miR_207 were anti-correlated with the ARF family, and miR390a-3p and novel_miR_101 were anti-correlated with the AUX/IAA family. These results provide a theoretical basis for further studies on the auxin regulatory mechanisms in rose.

Factor of DNA methylation 1 affects woodland strawberry plant stature and organ size via DNA methylation.

RNA-directed DNA methylation (RdDM) is an epigenetic process that directs silencing to specific genomic regions and loci. The biological functions of RdDM are not well studied in horticultural plants. Here, we isolated the ethyl methane-sulfonate-induced mutant reduced organ size (ros) producing small leaves, flowers, and fruits in woodland strawberry (Fragaria vesca) due to reduced cell numbers compared with that in the wild-type (WT). The candidate mutation causes a premature stop codon in FvH4_6g28780, which shares high similarity to Arabidopsis (Arabidopsis thaliana) Factor of DNA Methylation1 (FDM1) encoding an RdDM pathway component and was named FveFDM1. Consistently, the fvefdm1CR mutants generated by CRISPR/Cas9 also produced smaller organs. Overexpressing FveFDM1 in an Arabidopsis fdm1-1 fdm2-1 double mutant restored DNA methylation at the RdDM target loci. FveFDM1 acts in a protein complex with its homolog Involved in De Novo 2 (FveIDN2). Furthermore, whole-genome bisulfite sequencing revealed that DNA methylation, especially in the CHH context, was remarkably reduced throughout the genome in fvefdm1. Common and specific differentially expressed genes were identified in different tissues of fvefdm1 compared to in WT tissues. DNA methylation and expression levels of several gibberellic acid (GA) biosynthesis and cell cycle genes were validated. Moreover, the contents of GA and auxin were substantially reduced in the young leaves of fvefdm1 compared to in the WT. However, exogenous application of GA and auxin could not recover the organ size of fvefdm1. In addition, expression levels of FveFDM1, FveIDN2, Nuclear RNA Polymerase D1 (FveNRPD1), Domains Rearranged Methylase 2 (FveDRM2), and cell cycle genes were greatly induced by GA treatment. Overall, our work demonstrated the critical roles of FveFDM1 in plant growth and development via RdDM-mediated DNA methylation in horticultural crops.