YUC Genes Research Articles

Plant Hormone Pathway Is Involved in Regulating the Embryo Development Mechanism of the Hydrangea macrophylla Hybrid.

The research is aimed to elucidate the role of plant hormones in regulating the development of hybrid embryos in Hydrangea macrophylla. Fruits from the intraspecific cross of H. macrophylla 'Otaksa' × 'Coerulea' were selected at the globular, heart, and torpedo stages of embryo development. Transcriptome sequencing and differential gene expression analysis were conducted. The results showed that fruit growth followed a single "S-shaped growth curve, with globular, heart, and torpedo embryos appearing at 30, 40, and 50 d post-pollination, respectively, and the embryo maintaining the torpedo shape from 60 to 90 d. A total of 12,933 genes was quantified across the three developmental stages, with 3359, 3803, and 3106 DEGs in the S1_vs_S2, S1_vs_S3, and S2_vs_S3 comparisons, respectively. Among these, 133 genes related to plant hormone biosynthesis and metabolism were differentially expressed, regulating the synthesis and metabolism of eight types of plant hormones, including cytokinin, auxin, gibberellin, abscisic acid, and jasmonic acid. The pathways with the most differentially expressed genes were cytokinin, auxin, and gibberellin, suggesting these hormones may play crucial roles in embryo development. In the cytokinin pathway, CKX (Hma1.2p1_0579F.1_g182670.gene, Hma1.2p1_1194F.1_g265700.gene, and NewGene_12164) genes were highly expressed during the globular embryo stage, promoting rapid cell division in the embryo. In the auxin pathway, YUC (Hma1.2p1_0271F.1_g109005.gene and Hma1.2p1_0271F.1_g109020.gene) genes were progressively up-regulated during embryo growth; the early response factor AUX/IAA (Hma1.2p1_0760F.1_g214260.gene) was down-regulated, while the later transcriptional activator ARF (NewGene_21460, NewGene_21461, and Hma1.2p1_0209F.1_g089090.gene) was up-regulated, sustaining auxin synthesis and possibly preventing the embryo from transitioning to maturity. In the gibberellin pathway, GA3ox (Hma1.2p1_0129F.1_g060100.gene) expression peaked during the heart embryo stage and then declined, while the negative regulator GA2ox (Hma1.2p1_0020F.1_g013915.gene) showed the opposite trend; and the gibberellin signaling repressor DELLA (Hma1.2p1_1054F.1_g252590.gene) increased over time, potentially inhibiting embryo development and maintaining the torpedo shape until fruit maturity. These findings preliminarily uncover the factors affecting the development of hybrid H. macrophylla embryos, laying a foundation for further research into the regulatory mechanisms of H. macrophylla hybrid embryo development.

Identification of YUC genes associated with leaf wrinkling trait in Tacai variety of Chinese cabbage.

Chinese cabbage (Brassica campestris L. ssp. chinensis (L.) Makino) stands as a widely cultivated leafy vegetable in China, with its leaf morphology significantly influencing both quality and yield. Despite its agricultural importance, the precise mechanisms governing leaf wrinkling development remain elusive. This investigation focuses on 'Wutacai', a representative cultivar of the Tacai variety (Brassica campestris L. ssp. chinensis var. rosularis Tsen et Lee), renowned for its distinct leaf wrinkling characteristics. Within the genome of 'Wutacai', we identified a total of 18 YUCs, designated as BraWTC_YUCs, revealing their conservation within the Brassica genus, and their close homology to YUCs in Arabidopsis. Expression profiling unveiled that BraWTC_YUCs in Chinese Cabbage exhibited organ-specific and leaf position-dependent variation. Additionally, transcriptome sequencing data from the flat leaf cultivar 'Suzhouqing' and the wrinkled leaf cultivar 'Wutacai' revealed differentially expressed genes (DEGs) related to auxin during the early phases of leaf development, particularly the YUC gene. In summary, this study successfully identified the YUC gene family in 'Wutacai' and elucidated its potential function in leaf wrinkling trait, to provide valuable insights into the prospective molecular mechanisms that regulate leaf wrinkling in Chinese cabbage.

Application of Long-Chained Auxin Conjugates Influenced Auxin Metabolism and Transcriptome Response in Brassica rapa L. ssp. pekinensis.

Auxin amino acid conjugates are considered to be storage forms of auxins. Previous research has shown that indole-3-acetyl-L-alanine (IAA-Ala), indole-3-propionyl-L-alanine (IPA-Ala) and indole-3-butyryl-L-alanine (IBA-Ala) affect the root growth of Brassica rapa seedlings. To elucidate the potential mechanism of action of the conjugates, we treated B. rapa seedlings with 0.01 mM IAA-, IPA- and IBA-Ala and investigated their effects on the auxin metabolome and transcriptome. IBA-Ala and IPA-Ala caused a significant inhibition of root growth and a decrease in free IAA compared to the control and IAA-Ala treatments. The identification of free auxins IBA and IPA after feeding experiments with IBA-Ala and IPA-Ala, respectively, confirms their hydrolysis in vivo and indicates active auxins responsible for a stronger inhibition of root growth. IBA-Ala caused the induction of most DEGs (807) compared to IPA-Ala (417) and IAA-Ala (371). All treatments caused similar trends in transcription profile changes when compared to control treatments. The majority of auxin-related DEGs were found after IBA-Ala treatment, followed by IPA-Ala and IAA-Ala, which is consistent with the apparent root morphology. In addition to most YUC genes, which showed a tendency to be downregulated, transcripts of auxin-related DEGs that were identified (UGT74E2, GH3.2, SAUR, IAA2, etc.) were more highly expressed after all treatments. Our results are consistent with the hypothesis that the hydrolysis of conjugates and the release of free auxins are responsible for the effects of conjugate treatments. In conclusion, free auxins released by the hydrolysis of all auxin conjugates applied affect gene regulation, auxin homeostasis and ultimately root growth inhibition.

Genome-Wide Analysis and Expression Profiling of YUCCA Gene Family in Developmental and Environmental Stress Conditions in Tea Plant (Camellia sinensis)

The tea plant is a perennial leaf-used economical crop and cultivated all over the world. Indole-3-acetic acid (IAA) plays key roles in plant development and environmental stress. YUCCA (YUC) flavin monooxygenases are the rate-limiting enzymes of the TAA/YUC pathway, which is the most important IAA biosynthetic pathway in plants. The YUC gene family in tea plants has not been systematically studied so far. A total of 17 CsYUC members were identified from a tea plant genome database and phylogenetically classified into three subfamilies. Phylogenetic analysis showed that the CsYUC gene family is evolutionarily conserved. The physical and chemical properties, gene structures, and conserved domains were analyzed. The expression profiles of CsYUCs were analyzed on the basis of open available RNA-seq data, as well as by RNA-seq and qRT-PCR assays. Combined with previous studies, it can be concluded that YUC10 may play key roles in seed development. The results also showed that CsYUC2.1 may play important roles in the coordinated regulation of the growth of leaf buds and flower buds induced by pruning. Low temperature markedly induced the expression of CsYUC2.2, -11.8, and -11.9. Furthermore, CsYUC genes that might play key roles in the specific development stages and involve enhancing the resistance to drought and NaCl stress were screened, respectively. This study could provide a research basis for deeply studying the gene functions of the CsYUC family in the tea plant.

Auxin biosynthesis gene FveYUC4 is critical for leaf and flower morphogenesis in woodland strawberry.

Auxin plays an essential role in plant growth and development, particularly in fruit development. The YUCCA (YUC) genes encode flavin monooxygenases that catalyze a rate-limiting step in auxin biosynthesis. Mutations that disrupt YUC gene function provide useful tools for dissecting general and specific functions of auxin during plant development. In woodland strawberry (Fragaria vesca), two ethyl methanesulfonate mutants, Y422 and Y1011, have been identified that exhibit severe defects in leaves and flowers. In particular, the width of the leaf blade is greatly reduced, and each leaflet in the mutants has fewer and deeper serrations. In addition, the number and shape of the floral organs are altered, resulting in smaller fruits. Mapping by sequencing revealed that both mutations reside in the FveYUC4 gene, and were therefore renamed as yuc4-1 and yuc4-2. Consistent with a role for FveYUC4 in auxin synthesis, free auxin and its metabolites are significantly reduced in the yuc4 leaves and flowers. This role of FveYUC4 in leaf and flower development is supported by its high and specific expression in young leaves and flower buds using GUS reporters. Furthermore, germline transformation of pYUC4::YUC4, which resulted in elevated expression of FveYUC4 in yuc4 mutants, not only rescued the leaf and flower defects but also produced parthenocarpic fruits. Taken together, our data demonstrate that FveYUC4 is essential for leaf and flower morphogenesis in woodland strawberry by providing auxin hormone at the proper time and in the right tissues.

Analysis of YUC and TAA/TAR Gene Families in Tomato

Auxin is a vital phytohormone, but its synthesis pathway is poorly understood. This study used bioinformatic analysis to identify and analyze the gene family members that encode tomato auxin biosynthesis. The FZY gene family members encoding flavin-containing monooxygenases were retrieved from the tomato genome database. DNAMAN analysis revealed nine genes within the landmark domain WL(I/V)VATGENAE, between the FAD and NADPH domains. Phylogenetic analysis showed that the FZY gene family in tomato is closely related to the YUC gene family in Arabidopsis thaliana. A qRT-PCR showed that SlFZY2, SlFZY3, SlFZY4-1, and SlFZY5 were highly expressed in tomato flower organs. The analysis of promoter cis-acting elements revealed light-responsive elements in the promoters of all nine members in tomato, indicating their sensitivity to light signals. Furthermore, the promoters of SlFZY4-2, SlFZY5, and SlFZY7 contain low-temperature-responsive elements. This study demonstrated that SlTAA5 expression was 2.22 times that of SlTAA3 in the roots, and SlTAA3 expression in the pistils was 83.58 times that in the stamens during the tomato flowering stage. Therefore, various members of the tomato FZY gene family are involved in regulating the development of tomato floral organs and are responsive to abiotic stresses, such as low temperature and weak light.

Significance of NatB-mediated N-terminal acetylation of auxin biosynthetic enzymes in maintaining auxin homeostasis in Arabidopsis thaliana

The auxin IAA (Indole-3-acetic acid) plays key roles in regulating plant growth and development, which depends on an intricate homeostasis that is determined by the balance between its biosynthesis, metabolism and transport. YUC flavin monooxygenases catalyze the rate-limiting step of auxin biosynthesis via IPyA (indole pyruvic acid) and are critical targets in regulating auxin homeostasis. Despite of numerous reports on the transcriptional regulation of YUC genes, little is known about those at the post-translational protein level. Here, we show that loss of function of CKRC3/TCU2, the auxiliary subunit (Naa25) of Arabidopsis NatB, and/or of its catalytic subunit (Naa20), NBC, led to auxin-deficiency in plants. Experimental evidences show that CKRC3/TCU2 can interact with NBC to form a NatB complex, catalyzing the N-terminal acetylation (NTA) of YUC proteins for their intracellular stability to maintain normal auxin homeostasis in plants. Hence, our findings provide significantly new insight into the link between protein NTA and auxin biosynthesis in plants.

Auxin Biosynthesis Genes in Allotetraploid Oilseed Rape Are Essential for Plant Development and Response to Drought Stress.

Crucial studies have verified that IAA is mainly generated via the two-step pathway in Arabidopsis, in which tryptophan aminotransferase (TAA) and YUCCA (YUC) are the two crucial enzymes. However, the role of the TAA (or TAR) and YUC genes in allotetraploid oilseed rape underlying auxin biosynthesis and development regulation remains elusive. In the present study, all putative TAR and YUC genes were identified in B. napus genome. Most TAR and YUC genes were tissue that were specifically expressed. Most YUC and TAR proteins contained trans-membrane regions and were confirmed to be endoplasmic reticulum localizations. Enzymatic activity revealed that YUC and TAR protein members were involved in the conversion of IPA to IAA and Trp to IPA, respectively. Transgenic plants overexpressing BnaYUC6a in both Arabidopsis and B. napus displayed high auxin production and reduced plant branch angle, together with increased drought resistance. Moreover, mutation in auxin biosynthesis BnaTARs genes by CRISPR/Cas9 caused development defects. All these results suggest the convergent role of BnaYUC and BnaTAR genes in auxin biosynthesis. Different homoeologs of BnaYUC and BnaTAR may be divergent according to sequence and expression variation. Auxin biosynthesis genes in allotetraploid oilseed rape play a pivotal role in coordinating plant development processes and stress resistance.

Systematical characterization of YUCCA gene family in five cotton species, and potential functions of YUCCA22 gene in drought resistance of cotton

Auxin plays an essential role in the normal growth and development of plants. The tryptophan aminotransferase of Arabidopsis (TAA)/YUCCA (YUC) enzymes functions as flavin monooxygenases (FMOs), which are the key enzymes in auxin synthesis. However, comprehensive characterization of the YUC gene family in cotton has not yet been completed. In order to reveal the functions of YUC genes in cotton, we systematically identified and characterized the YUC gene family in five species of cotton including analysis of the member, characterization, intragenomic duplication, and collinear relationships. Transcriptomic analysis indicates that GhYUCs participate in abiotic stress processes in cotton. The GhYUC22 gene that is responsive to polyethylene glycol (PEG) and abscisic acid (ABA) was functionally identified via virus-induced gene silencing (VIGS). Subsequent natural drought simulation experiments and physiological index data demonstrated that partial silencing of GhYUC22 gene endowed cotton with drought resistance by modulating indole-3-acetic acid (IAA) and ABA signaling pathways. In conclusion, our findings support the role of that GhYUC22 gene in modulating both endogenous auxin and ABA homeostasis and regulating the drought resistance in cotton.

Nicotiana benthamiana as a Transient Expression Host to Produce Auxin Analogs.

Plant secondary metabolites have applications for the food, biofuel, and pharmaceutical industries. Recent advances in pathway elucidation and host expression systems now allow metabolic engineering of plant metabolic pathways to produce “new-to-nature” derivatives with novel biological activities, thereby amplifying the range of industrial uses for plant metabolites. Here we use a transient expression system in the model plant Nicotiana benthamiana to reconstitute the two-step plant-derived biosynthetic pathway for auxin (indole acetic acid) to achieve accumulation up to 500 ng/g fresh mass (FM). By expressing these plant-derived enzymes in combination with either bacterial halogenases and alternative substrates, we can produce both natural and new-to-nature halogenated auxin derivatives up to 990 ng/g FM. Proteins from the auxin synthesis pathway, tryptophan aminotransferases (TARs) and flavin-dependent monooxygenases (YUCs), could be transiently expressed in combination with four separate bacterial halogenases to generate halogenated auxin derivatives. Brominated auxin derivatives could also be observed after infiltration of the transfected N. benthamiana with potassium bromide and the halogenases. Finally, the production of additional auxin derivatives could also be achieved by co-infiltration of TAR and YUC genes with various tryptophan analogs. Given the emerging importance of transient expression in N. benthamiana for industrial scale protein and product expression, this work provides insight into the capacity of N. benthamiana to interface bacterial genes and synthetic substrates to produce novel halogenated metabolites.

YUCCA-Mediated Biosynthesis of the Auxin IAA Is Required during the Somatic Embryogenic Induction Process in Coffea canephora.

Despite the existence of considerable research on somatic embryogenesis (SE), the molecular mechanism that regulates the biosynthesis of auxins during the SE induction process remains unknown. Indole-3-acetic acid (IAA) is an auxin that is synthesized in plants through five pathways. The biosynthetic pathway most frequently used in this synthesis is the conversion of tryptophan to indol-3-pyruvic acid (IPA) by tryptophan aminotransferase of Arabidopsis (TAA) followed by the conversion of IPA to IAA by enzymes encoded by YUCCA (YUC) genes of the flavin monooxygenase family; however, it is unclear whether YUC-mediated IAA biosynthesis is involved in SE induction. In this study, we report that the increase of IAA observed during SE pre-treatment (plants in MS medium supplemented with 1-naphthaleneacetic acid (NAA) 0.54 µM and kinetin (Kin) 2.32 µM for 14 days) was due to its de novo biosynthesis. By qRT-PCR, we demonstrated that YUC gene expression was consistent with the free IAA signal found in the explants during the induction of SE. In addition, the use of yucasin to inhibit the activity of YUC enzymes reduced the signal of free IAA in the leaf explants and dramatically decreased the induction of SE. The exogenous addition of IAA restored the SE process in explants treated with yucasin. Our findings suggest that the biosynthesis and localization of IAA play an essential role during the induction process of SE in Coffea canephora.

The viral suppressor HCPro decreases DNA methylation and activates auxin biosynthesis genes

Auxin has profound effects on plant growth and development. In addition to participating in plant growth and development, the auxin signaling pathway is involved in plant defense against pathogens. In this study, we investigated the molecular mechanism by which helper-component protease (HCPro) encoded by the Tobacco vein banding mosaic virus (TVBMV) activates auxin biosynthesis genes (YUCs) and interferes with the auxin signaling pathway. Our results demonstrated that the viral suppressor HCPro decreased the DNA methylation of dispersed repeats (DRs) within the promoters of YUC1, YUC5 and YUC10 and transcriptional activated these YUC genes targeted by RNA-directed DNA methylation (RdDM), leading to an increase in auxin accumulation in plants. Furthermore, we found that the induction of these YUCs by HCPro was attenuated in ros1 mutant plants, suggesting that HCPro-mediated transcriptional activation of the genes was partly dependent on ROS1-mediated DNA demethylation.

The Roles of Auxin Biosynthesis YUCCA Gene Family in Plants

Auxin plays essential roles in plant normal growth and development. The auxin signaling pathway relies on the auxin gradient within tissues and cells, which is facilitated by both local auxin biosynthesis and polar auxin transport (PAT). The TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA)/YUCCA (YUC) pathway is the most important and well-characterized pathway that plants deploy to produce auxin. YUCs function as flavin-containing monooxygenases (FMO) catalyzing the rate-limiting irreversible oxidative decarboxylation of indole-3-pyruvate acid (IPyA) to form indole-3-acetic acid (IAA). The spatiotemporal dynamic expression of different YUC gene members finely tunes the local auxin biosynthesis in plants, which contributes to plant development as well as environmental responses. In this review, the recent advances in the identification, evolution, molecular structures, and functions in plant development and stress response regarding the YUC gene family are addressed.

Cell Death Triggered by the YUCCA-like Bs3 Protein Coincides with Accumulation of Salicylic Acid and Pipecolic Acid But Not of Indole-3-Acetic Acid.

The pepper (Capsicum annuum) resistance gene bacterial spot3 (Bs3) is transcriptionally activated by the matching Xanthomonas euvesicatoria transcription-activator-like effector (TALE) AvrBs3. AvrBs3-induced Bs3 expression triggers a rapid and local cell death reaction, the hypersensitive response (HR). Bs3 is most closely related to plant flavin monooxygenases of the YUCCA (YUC) family, which catalyze the final step in auxin biosynthesis. Targeted mutagenesis of predicted NADPH- and FAD-cofactor sites resulted in Bs3 derivatives that no longer trigger HR, thereby suggesting that the enzymatic activity of Bs3 is crucial to Bs3-triggered HR. Domain swap experiments between pepper Bs3 and Arabidopsis (Arabidopsis thaliana) YUC8 uncovered functionally exchangeable and functionally distinct regions in both proteins, which is in agreement with a model whereby Bs3 evolved from an ancestral YUC gene. Mass spectrometric measurements revealed that expression of YUCs, but not expression of Bs3, coincides with an increase in auxin levels, suggesting that Bs3 and YUCs, despite their sequence similarity, catalyze distinct enzymatic reactions. Finally, we found that expression of Bs3 coincides with increased levels of the salicylic acid and pipecolic acid, two compounds that are involved in systemic acquired resistance.

Emerging functions of chromatin modifications in auxin biosynthesis in response to environmental alterations

Auxin is one of the most important hormone groups in plants. It has been documented to play various functions in plant growth and development. In this phytohormone group, indole-3-acetic acid (IAA) is widely considered as a main natural auxin. To date, many lines of evidence have revealed that the alterations of ambient environment such as light and temperature conditions can affect the IAA biosynthesis which consequently redirects the growth and development of the plants so that they can adapt to the new environmental conditions. Current studies have shown the large impact of chromatin modifications in the regulation of eukaryotic gene expression. Previous studies have elucidated different epigenetic factors in the regulation of auxin signaling pathway in the plants. This review aimed to provide a precise and systemic overview of the chromatin modifications at the auxin biosynthesis gene loci, namely YUCCA (YUC) genes, and their effects on the expression of these genes. Based on these emerging data, we propose different hypothetical models demonstrating the functions of epigenetic factors as well as chromatin modifications in the regulation of YUC genes which can subsequently determine the auxin accumulation in the plants.

The YUCCA-Auxin-WOX11 Module Controls Crown Root Development in Rice.

A well-developed root system in rice and other crops can ensure plants to efficiently absorb nutrients and water. Auxin is a key regulator for various aspect of root development, but the detailed molecular mechanisms by which auxin controls crown root development in rice are not understood. We show that overexpression of a YUC gene, which encodes the rate-limiting enzyme in auxin biosynthesis, causes massive proliferation of crown roots. On the other hand, we find that disruption of TAA1, which functions upstream of YUC genes, greatly reduces crown root development. We find that YUC overexpression-induced crown root proliferation requires the presence of the transcription factor WOX11. Moreover, the crown rootless phenotype of taa1 mutants was partially rescued by overexpression of WOX11. Furthermore, we show that WOX11 expression is induced in OsYUC1 overexpression lines, but is repressed in the taa1 mutants. Our results indicate that auxin synthesized by the TAA/YUC pathway is necessary and sufficient for crown root development in rice. Auxin activates WOX11 transcription, which subsequently drives crown root initiation and development, establishing the YUC-Auxin-WOX11 module for crown root development in rice.

Auxin is Involved in Lateral Root Formation Induced by Drought Stress in Tobacco Seedlings

Drought stress is a common abiotic stress that affects plant root development. The goal of this study was to identify the role of auxin on aspects of root growth under water-deficient conditions in Nicotiana tabacum L. In this study, time-course development of lateral root (LR) growth in response to water deficiency (2.5% polyethylene glycol 6000, PEG) was analyzed in tobacco seedlings. LR formation in tobacco plants in response to drought stress depended on the experimental duration. First- and second-order LR formation was induced, respectively, by 43 and 28% on day 5 and by 57 and 40% on day 7 relative to control treatment. Thereafter, PEG-induced LR formation was not observed, and a decrease of 16% was recorded in first-order LR formation on day 11. A root pruning study suggested that PEG-induced LR formation plays a pivotal role in maintaining tobacco plant growth during drought stress. The change in the indole-3-acetic acid (IAA) concentration in leaves and roots was consistent with that of LR formation. This was corroborated by elevated DR5::GUS expression levels on day 5 and by decreased expression levels on day 9. Application of N-1-naphthylphthalamic acid (NPA) to PEG-treated seedlings reduced LR formation to levels similar to those of the control treatment; DR5::GUS expression was also similar between these treatments after NPA application. Results were similar following α-naphthylacetic acid application to control-treated seedlings. Measurement of [3H]IAA transport indicated that polar auxin transport from shoots to roots was increased by 43% under PEG application. Quantitative reverse transcription PCR revealed higher expression of YUC and PIN genes in PEG-treated plants, indicating that they play key roles in auxin synthesis and transport regulation in drought stress. Overall, these suggest that drought stress regulates LR formation in tobacco seedlings via modification of auxin synthesis and polar transport depending on the experimental stage.

Transcriptomic and Hormonal Analyses Reveal that YUC-Mediated Auxin Biogenesis Is Involved in Shoot Regeneration from Rhizome in Cymbidium.

Cymbidium, one of the most important orchid genera in horticulture, can be classified into epiphytic and terrestrial species. Generally, epiphytic Cymbidium seedlings can be easily propagated by tissue culture, but terrestrial seedlings are difficult to propagate. To date, the molecular mechanisms underlying the differences in the ease with which terrestrial and epiphytic cymbidiums can be propagated are largely unknown. Using RNA-sequencing, quantitative reverse transcription PCR and enzyme-linked immunosorbent assay, Cymbidium ‘Xiaofeng’ (CXF), which can be efficiently micropropagated, and terrestrial Cymbidium sinense ‘Qijianbaimo’ (CSQ), which has a low regeneration ability, were used to explore the molecular mechanisms underlying the micropropagation ability of Cymbidium species. To this end, 447 million clean short reads were generated, and 31,264 annotated unigenes were obtained from 10 cDNA libraries. A total of 1,290 differentially expressed genes (DEGs) were identified between CXF and CSQ during shoot induction. Gene ontology (GO) enrichment analysis indicated that the DEGs were significantly enriched in auxin pathway-related GO terms. Further analysis demonstrated that YUC and GH3 family genes, which play crucial roles in the regulation of auxin/IAA (indole-3-acetic acid) metabolism, acted quickly in response to shoot induction culture in vitro and were closely correlated with variation in shoot regeneration between CXF and CSQ. In addition, the study showed that IAA accumulated rapidly and significantly during shoot induction in CXF compared to that in CSQ; in contrast, no significant changes in other hormones were observed between CXF and CSQ. Furthermore, shoot regeneration in CXF was inhibited by a yucasin-auxin biosynthesis inhibitor, indicating that increased IAA level is required for high-frequency shoot regeneration in CXF. In conclusion, our study revealed that YUC-mediated auxin biogenesis is involved in shoot regeneration from rhizome in Cymbidium.

Auxin signaling through SCFTIR1/AFBs mediates feedback regulation of IAA biosynthesis.

We previously reported that exogenous application of auxin to Arabidopsis seedlings resulted in downregulation of indole-3-acetic acid (IAA) biosynthesis genes in a feedback manner. In this study, we investigated the involvement of the SCFTIR1/AFB-mediated signaling pathway in feedback regulation of the indole-3-pyruvic acid-mediated auxin biosynthesis pathway in Arabidopsis. Application of PEO-IAA, an inhibitor of the IAA signal transduction pathway, to wild-type seedlings resulted in increased endogenous IAA levels in roots. Endogenous IAA levels in the auxin-signaling mutants axr2-1, axr3-3, and tir1-1afb1-1afb2-1afb3-1 also increased. Furthermore, YUCCA (YUC) gene expression was repressed in response to auxin treatment, and expression of YUC7 and YUC8 increased in response to PEO-IAA treatment. YUC genes were also induced in auxin-signaling mutants but repressed in TIR1-overexpression lines. These observations suggest that the endogenous IAA levels are regulated by auxin biosynthesis in a feedback manner, and the Aux/IAA and SCFTIR1/AFB-mediated auxin-signaling pathway regulates the expression of YUC genes.

YUCCA-mediated auxin biogenesis is required for cell fate transition occurring during de novo root organogenesis in Arabidopsis.

Many plant organs have the ability to regenerate a new plant after detachment or wounding via de novo organogenesis. During de novo root organogenesis from Arabidopsis thaliana leaf explants, endogenic auxin is essential for the fate transition of regeneration-competent cells to become root founder cells via activation of WUSCHEL-RELATED HOMEOBOX 11 (WOX11). However, the molecular events from leaf explant detachment to auxin-mediated cell fate transition are poorly understood. In this study, we used an assay to determine the concentration of indole-3-acetic acid (IAA) to provide direct evidence that auxin is produced after leaf explant detachment, a process that involves YUCCA (YUC)-mediated auxin biogenesis. Inhibition of YUC prevents expression of WOX11 and fate transition of competent cells, resulting in the blocking of rooting. Further analysis showed that YUC1 and YUC4 act quickly (within 4 hours) in response to wounding after detachment in both light and dark conditions and promote auxin biogenesis in both mesophyll and competent cells, whereas YUC5, YUC8, and YUC9 primarily respond in dark conditions. In addition, YUC2 and YUC6 contribute to rooting by providing a basal auxin level in the leaf. Overall, our study indicates that YUC genes exhibit a division of labour during de novo root organogenesis from leaf explants in response to multiple signals.