Accumulation Of IAA Research Articles

Resveratrol and nitric oxide synergistically enhance resistance against B. cinerea in tomato fruit by regulating phytohormones

Resveratrol (RVT), a plant antitoxin, plays an important role in plant resistance against pathogens. While nitric oxide (NO) as an essential signaling factor in disease resistance enhancement is well documented, the potential molecular interplay RVT and NO in postharvest tomato fruit defense against Botrytis cinerea (B.cinerea) still needs exploration. In this study, exogenous RVT reduced gray mold caused by B.cinerea in tomato fruit, with 20 μM being the most effective. Tomato fruit were treated with 20 μM RVT enhanced resistance against B.cinerea, as indicated by reduced symptoms of disease and improved activity of disease resistance related enzymes (PAL, PPO and CHI). In addition, RVT treatment improved the expression of SlPR1, SlLoxd and SlMYC2, and promoted the accumulation of plant hormone IAA and ABA, but reduced the expression of SlNPR1 and the level of GA3. More importantly, the combined treatment of NO donor (SNP) and RVT notably enhanced disease resistance compared to RVT or SNP single treatment. However, the combination of NO inhibitor (L-NNA) and RVT treatment even reduced the positive effect of RVT. Meanwhile, the expression of SlPR1, SlLoxd and SlMYC2 and the accumulation of IAA and ABA in RVT + SNP treated fruit were higher than those in the RVT or SNP single treatment. Thus, our data demonstrate that RVT and NO synergistically enhance resistance against B. cinerea in tomato fruit by regulating phytohormones.

Multi-Omics analysis reveals the important role of indole-3-acetic acid homeostasis in male fertility of cotton

Auxin (Indole-3-acetic acid, IAA) is essential for anther development and male fertility, but little is known about its homeostasis in developing anthers due to its complex and diverse synthesis pathways. Here, we employed transcriptomic, targeted metabolomic, and amino acid analyses on a wild type (WT) cotton (Gossypium hirsutum) line SD98–6 and its nearly-isogenic male sterile (MS) line SD98–6A, to delve into the relationship between IAA and anther fertility. In WT anthers, IAA homeostasis was achieved mainly through self-synthesis, conjugate hydrolysis, and polar transport, and accumulation of IAA exhibited an inverted "U" pattern with the highest content observed at the tetrad stage. In MS anthers, no IAA accumulation was observed after the meiosis stage and the IAA content remained constantly low, mainly due to reduction of the substrates (phenylalanine and tryptophan) for IAA synthesis, and significantly decreased expression of the genes involved in IAA synthesis. Meanwhile, carbohydrate metabolism pathways directly contributing to IAA synthesis and synthesis of amino acids were malfunctional in MS anthers based on the expression profile of the metabolic genes and content measurement. These results provide valuable insights into the IAA homeostasis in cotton anthers and imply that genes related to IAA homeostasis are potential targets for development of IAA-sensitive male sterile cotton lines.

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

In 'Hass' avocado (Persea americana), fruit presence reduces next season flowering. Recent fruit tree studies proposed that heavy fruit load (HFL) generates an auxin (indole-3-acetic acid, IAA) signal in the buds that represses flowering. However, the nature of this signal remains unknown. Here, we investigated the effect of avocado HFL on bud IAA accumulation and flowering transition. We found that IAA-aspartate and IAA-glutamate conjugate levels were significantly higher in buds from fully loaded ('on') than low-loaded ('off') trees, hinting that free IAA levels were higher in the former. Expression analysis showed that coinciding with flowering reduction, HFL induced the floral repressor PaTFL1, and suggested that accumulation of IAA in buds as imposed by HFL was associated with its conjugation to aspartate and glutamate and resulted both from de novo IAA synthesis and from reduced IAA export. Accordingly, experiments involving radiolabelled [14C]IAA demonstrated that HFL reduced shoot basipetal IAA transport. Finally, we confirmed the negative effects of IAA on flowering, showing that IAA and polar auxin transport blocker (2,3,5-triiodobenzoic acid) treatments delayed 'off' trees' inflorescence development, reducing their inflorescence axis and inducing PaTFL1 expression. Together, our data indicate that avocado HFL generates IAA signalling in buds that induces PaTFL1, leading to repression of inflorescence development.

A rice exocyst subunit gene SEC3A is required for anther dehiscence

Anther dehiscence controls optimal interaction between pollen and stigma, thereby determining the successful sexual reproduction. The regulators or mechanisms of this process remain elusive. Here, two CRISPR/Cas9 mutants of a rice exocyst subunit gene SEC3A, sec3a-1 and sec3a-2, showed anther indehiscence at anthesis and male sterility at maturity. Pollen viability and germination in the mutants were partly defective, whereas their female gametes undergone a normal development. Hybrid or self-pollinated seeds could be produced by artificial pollination, suggesting potential use of a weak sec3a mutant as a female line during hybrid breeding. SEC3A is widely expressed in various tissues, including anther walls. Further results showed an excessive IAA accumulation and no endothecium lignification in sec3a-1/2 anthers. Our findings suggest that SEC3A appears to regulate anther dehiscence by modulating auxin signaling, providing insights into regulation of anther dehiscence and function of exocyst in plants.

Silencing of early auxin responsive genes MdGH3-2/12 reduces the resistance to Fusarium solani in apple

Apple replant disease (ARD) has led to severe yield and quality reduction in the apple industry. Fusarium solani (F. solani) has been identified as one of the main microbial pathogens responsible for ARD. Auxin (indole-3-acetic acid, IAA), an endogenous hormone in plants, is involved in almost all plant growth and development processes and plays a role in plant immunity against pathogens. Gretchen Hagen3 (GH3) is one of the early/primary auxin response genes. The aim of this study was to evaluate the function of MdGH3-2 and MdGH3-12 in the defense response of F. solani by treating MdGH3-2/12 RNAi plants with F. solani. The results show that under F. solani infection, RNAi of MdGH3-2/12 inhibited plant biomass accumulation and exacerbated root damage. After inoculation with F. solani, MdGH3-2/12 RNAi inhibited the biosynthesis of acid-amido synthetase. This led to the inhibition of free IAA combining with amino acids, resulting in excessive free IAA accumulation. This excessive free IAA altered plant tissue structure, accelerated fungal hyphal invasion, reduced the activity of antioxidant enzymes (SOD, POD and CAT), increased the reactive oxygen species (ROS) level, and reduced total chlorophyll content and photosynthetic ability, while regulating the expression of PR-related genes including PR1, PR4, PR5 and PR8. It also changed the contents of plant hormones and amino acids, and ultimately reduced the resistance to F. solani. In conclusion, these results demonstrate that MdGH3-2 and MdGH3-12 play an important role in apple tolerance to F. solani and ARD.

Growth performance and metabolic changes in lettuce inoculated with plant growth promoting bacteria in a hydroponic system

Crop cultivation in hydroponic systems is often exposed to both abiotic and biotic stresses, which impact growth. One possible approach to alleviating these stresses and improving plant growth is by utilizing plant growth-promoting bacteria (PGPB). Our previous study has shown the efficacy of two PGPB strains, Pseudomonas lundensis UB 53 and Pseudomonas migulae UB 54, in promoting growth and stimulating the generation of plant defense enzymes to mitigate biotic and abiotic stress in lettuce grown in a nutrient film technique (NFT) hydroponic system. Therefore, this study purposed to assess metabolic changes in lettuce in response to P. lundensis UB 53 and P. migulae UB 54 inoculation in a NFT hydroponic system. The results exhibited that these bacteria enhanced IAA accumulation and lettuce growth in a NFT hydroponic system. A total of 58 metabolites were detected in the root samples, including primary and secondary metabolites. It also influenced 12 metabolic pathways, with emphasis on five pathways, including the metabolism of alpha-linolenic acid, inositol phosphate, pyruvate, sulfur, and the phosphatidylinositol signaling system. These results highlight the significant roles of myo-inositol and acetic acid in metabolic pathways during the interaction between lettuce and PGPB.

A comprehensive investigation of the regulatory roles of OsERF096, an AP2/ERF transcription factor, in rice cold stress response.

OsERF096 negatively regulates rice cold tolerance and mediates IAA biosynthesis and signaling under cold stress. The APETALA2/ethylene-responsive factor (AP2/ERF) transcription factors play important roles in regulating plant tolerance to abiotic stress. OsERF096 was previously identified as a direct target of miR1320, and was suggested to negatively regulate rice cold tolerance. In this study, we performed RNA-sequencing and targeted metabolomics assays to reveal the regulatory roles of OsERF096 in cold stress response. GO and KEGG analysis of differentially expressed genes showed that the starch and sucrose metabolism, plant-pathogen interaction, and plant hormone signal transduction pathways were significantly enriched. Quantification analysis confirmed a significant difference in sugar contents among WT and OsERF096 transgenic lines under cold treatment. Targeted metabolomics analysis uncovered that IAA accumulation and signaling were modified by OsERF096 in response to cold stress. Expectedly, qRT-PCR assays confirmed significant OsIAAs and OsARFs expression changes in OsERF096 transgenic lines. Finally, we identified three targets of OsERF096 based on RNA-seq, qRT-PCR, and dual-LUC assays. In summary, these results revealed the multiple regulatory roles of OsERF096 in cold stress response.

Overexpression of MdFRK2 enhances apple drought resistance by promoting carbohydrate metabolism and root growth under drought stress

Soluble sugars function not only as the energy and structural blocks supporting plants, but also as osmoregulators and signal molecules during plant adaptation to water deficit. Here, we investigated drought resistance in transgenic apple (Malus × domestica) overexpressing MdFRK2, a key gene regulating fructose content and sugar metabolism. There is no obvious phenotypic difference between MdFRK2-overexpressing transgenic plants and WT plants under the well-watered condition. However, the transgenic plants and the grafted plants using MdFRK2-overexpressing rootstock exhibited improved tolerance to drought stress. Overexpression of MdFRK2 significantly promoted the growth of root system under drought stress. RNA sequencing showed that under drought stress, genes involved in sugar metabolism, transcription regulation, signal transduction or hormone metabolism were differentially expressed in MdFRK2 transgenic plants. Consistent with the gene expression profile, the activities of enzyme (SDH, FRK and NI) involved in sugar metabolism in the roots of MdFRK2 transgenic plants were significantly higher than those of untransformed control plants after drought stress. Under drought stress, overexpression of MdFRK2 promoted the accumulation of IAA, and decreased the contents of ABA and CK in apple root system. In conclusion, these results suggest that MdFRK2 can promote the growth of apple roots under drought stress by regulating sugar metabolism and accumulation, hormone metabolism and signal transduction, and then resist drought stress.

Light Quality and Sucrose-Regulated Detached Ripening of Strawberry with Possible Involvement of Abscisic Acid and Auxin Signaling.

The regulation of detached ripening is significant for prolonging fruit shelf life. Although light quality and sucrose affecting strawberry fruit ripening have been widely reported, little information is available about how they co-regulate the strawberry detached ripening process. In this study, different light qualities (red light-RL, blue light-BL, and white light-WL) and 100 mM sucrose were applied to regulate the ripening of initial red fruits detached from the plant. The results showed RL-treated samples (RL + H2O, RL + 100 mM sucrose) had brighter and purer skin color with a higher L*, b*, and C* value, and promoted the ascorbic acid. Almost all light treatments significantly decreased TSS/TA (total soluble solid/titratable acid) and soluble sugar/TA ratio, which is exacerbated by the addition of sucrose. Blue or red light in combination with sucrose notably increased total phenolic content and decreased malondialdehyde (MDA) accumulation. In addition, blue or red light combined with sucrose increased abscisic acid (ABA) content and promoted ABA signaling by inducing ABA-INSENSITIVE 4 (ABI4) expression and inhibiting SUCROSE NONFERMENTING1-RELATED PROTEIN KINASE 2.6 (SnRK2.6) expression. The strawberries exposed to blue and red light significantly improved auxin (IAA) content compared to the control (0 d), whereas the addition of sucrose inhibited IAA accumulation. Moreover, sucrose treatment suppressed the AUXIN/INDOLE-3-ACETIC ACID 11 (AUX/IAA11) and AUXIN RESPONSE FACTOR 6 (ARF6) expression under different light qualities. Overall, these results indicated that RL/BL + 100 mM sucrose might promote the detached ripening of strawberries by regulating abscisic acid and auxin signaling.

SlGH3.15, a member of the GH3 gene family, regulates lateral root development and gravitropism response by modulating auxin homeostasis in tomato

Multiple Gretchen Hagen 3 (GH3) genes have been implicated in a range of processes in plant growth and development through their roles in maintaining hormonal homeostasis. However, there has only been limited study on the functions of GH3 genes in tomato (Solanum lycopersicum). In this work, we investigated the important function of SlGH3.15, a member of the GH3 gene family in tomato. Overexpression of SlGH3.15 led to severe dwarfism in both the above- and below-ground sections of the plant, accompanied by a substantial decrease in free IAA content and reduction in the expression of SlGH3.9, a paralog of SlGH3.15. Exogenous supply of IAA negatively affected the elongation of the primary root and partially restored the gravitropism defects in SlGH3.15-overexpression lines. While no phenotypic change was observed in the SlGH3.15 RNAi lines, double knockout lines of SlGH3.15 and SlGH3.9 were less sensitive to treatments with the auxin polar transport inhibitor. Overall, these findings revealed important roles of SlGH3.15 in IAA homeostasis and as a negative regulator of free IAA accumulation and lateral root formation in tomato.

Auxin efflux carrier ZmPIN1a modulates auxin reallocation involved in nitrate-mediated root formation

BackgroundAuxin plays a crucial role in nitrate (NO3–)-mediated root architecture, and it is still unclear that if NO3– supply modulates auxin reallocation for regulating root formation in maize (Zea mays L.). This study was conducted to investigate the role of auxin efflux carrier ZmPIN1a in the root formation in response to NO3– supply.ResultsLow NO3– (LN) promoted primary root (PR) elongation, while repressed the development of lateral root primordia (LRP) and total root length. LN modulated auxin levels and polar transport and regulated the expression of auxin-responsive and -signaling genes in roots. Moreover, LN up-regulated the expression level of ZmPIN1a, and overexpression of ZmPIN1a enhanced IAA efflux and accumulation in PR tip, while repressed IAA accumulation in LRP initiation zone, which consequently induced LN-mediated PR elongation and LR inhibition. The inhibition rate of PR length, LRP density and number of ZmPIN1a-OE plants was higher than that of wild-type plants after auxin transport inhibitor NPA treatment under NN and LN conditions, and the degree of inhibition of root growth in ZmPIN1a-OE plants was more obvious under LN condition.ConclusionThese findings suggest that ZmPIN1a was involved in modulating auxin levels and transport to alter NO3–-mediated root formation in maize.

Root ABA Accumulation Delays Lateral Root Emergence in Osmotically Stressed Barley Plants by Decreasing Root Primordial IAA Accumulation

Increased auxin levels in root primordia are important in controlling root branching, while their interaction with abscisic acid (ABA) likely regulates lateral root development in water-deficient plants. The role of ABA accumulation in regulating root branching was investigated using immunolocalization to detect auxin (indoleacetic acid, IAA) and ABA (abscisic acid) in root primordia of the ABA-deficient barley mutant Az34 and its parental genotype (cv. Steptoe) barley plants. Osmotic stress strongly inhibited lateral root branching in Steptoe plants, but hardly affected Az34. Root primordial cells of Steptoe plants had increased immunostaining for ABA but diminished staining for IAA. ABA did not accumulate in root primordia of the Az34, and IAA levels and distribution were unaltered. Treating Az34 plants with exogenous ABA decreased root IAA concentration, while increasing root primordial ABA accumulation and decreasing root primordial IAA concentration. Although ABA treatment of Az34 plants increased the root primordial number, it decreased the number of visible emerged lateral roots. These effects were qualitatively similar to that of osmotic stress on the number of lateral root primordia and emerged lateral roots in Steptoe. Thus ABA accumulation (and its crosstalk with auxin) in root primordia seems important in regulating lateral root branching in response to water stress.

The B-box transcription factor IbBBX29 regulates leaf development and flavonoid biosynthesis in sweet potato.

Plant flavonoids are valuable natural antioxidants. Sweet potato (Ipomoea batatas) leaves are rich in flavonoids, regenerate rapidly, and can adapt to harsh environments, making them an ideal material for flavonoid biofortification. Here, we demonstrate that the B-box (BBX) family transcription factor IbBBX29 regulates the flavonoid contents and development of sweet potato leaves. IbBBX29 was highly expressed in sweet potato leaves and significantly induced by auxin (IAA). Overexpression of IbBBX29 contributed to a 21.37%-70.94% increase in leaf biomass, a 12.08%-21.85% increase in IAA levels, and a 31.33%-63.03% increase in flavonoid accumulation in sweet potato, whereas silencing this gene produced opposite effects. Heterologous expression of IbBBX29 in Arabidopsis (Arabidopsis thaliana) led to a dwarfed phenotype, along with enhanced IAA and flavonoid accumulation. RNA-seq analysis revealed that IbBBX29 modulates the expression of genes involved in the IAA signaling and flavonoid biosynthesis pathways. Chromatin immunoprecipitation-quantitative polymerase chain reaction and electrophoretic mobility shift assay indicated that IbBBX29 targets key genes of IAA signaling and flavonoid biosynthesis to activate their expression by binding to specific T/G-boxes in their promoters, especially those adjacent to the transcription start site. Moreover, IbBBX29 physically interacted with developmental and phenylpropanoid biosynthesis-related proteins, such as AGAMOUS-LIKE 21 protein IbAGL21 and MYB308-like protein IbMYB308L. Finally, overexpressing IbBBX29 also increased flavonoid contents in sweet potato storage roots. These findings indicate that IbBBX29 plays a pivotal role in regulating IAA-mediated leaf development and flavonoid biosynthesis in sweet potato and Arabidopsis, providing a candidate gene for flavonoid biofortification in plants.

Exogenous ABA and IAA modulate physiological and hormonal adaptation strategies in Cleistocalyx operculatus and Syzygium jambos under long-term waterlogging conditions

BackgroundThe mechanisms of abscisic acid (ABA) and auxin (IAA) in inducing adventitious root (AR) formation, biomass accumulation, and plant development under long-term waterlogging (LT-WL) conditions are largely unexplored. This study aimed to determine the roles of exogenous application of ABA and IAA in two woody plants (Cleistocalyx operculatus and Syzygium jambos) under LT-WL conditions. A pot experiment was conducted using a complete randomized design with two factors: (i) LT-WL and (ii) application of exogenous phytohormones (ABA and IAA) for 120 d.ResultsResults revealed that exogenous ABA and IAA promoted LT-WL tolerance in both species. In C. operculatus and S. jambos, plant height, the number of blades, leaf area, and fresh shoot weight were increased by exogenous IAA under LT-WL. However, exogenous ABA affected more the adventitious and primary root in C. operculatus compared to S. jambos. LT-WL decreased drastically the photosynthetic activities in both species, but adding moderate amounts of exogenous ABA or IAA protected the photosynthesis apparatus under LT-WL. Exogenous phytohormones at certain levels decreased the superoxide anion level and malondialdehyde accumulation in plants under LT-WL. Also, the increase of the peroxidases and superoxide dismutase activities by exogenous phytohormones was more marked in C. operculatus compared to S. jambos. Meanwhile, the catalase activity was down-regulated in both species by exogenous phytohormones. Exogenous ABA or IAA positively regulated the jasmonic acid content in ARs under LT-WL. Moderate application of exogenous ABA or IAA in plants under LT-WL decreased the ABA content in the leaves. Lower accumulation of IAA and ABA in the leaves of C. operculatus under LT-WL was positively correlated with a decrease in antioxidant activity.ConclusionsLastly, C. operculatus which has greater morphology indexes was more tolerant to waterlogging than S. jambos. Moreover, the adaptive strategies via exogenous ABA were more built around the below-ground biomass indexes particularly in C. operculatus, while exogenous IAA backed the above-ground biomass in both species. Overall, the exogenous hormones applied (spraying or watering) influenced differentially the plant’s responses to LT-WL. The phytohormonal profile of plants exposed to waterlogging stress varied depending on the species’ tolerance level.

AmiRNAi silencing of FaCRY2 delayed the growth of cultivated strawberry

As a plant blue light receptor, CRY2 plays pleotropic roles in regulating photomorphogenesis, flowering time and stress response. However, the function of CRY2 in the octoploid cultivated strawberry (Fragaria × ananassa Duch.) has not been identified. In this study, certain variation and functional divergences of the FaCRY2 protein were found in compared with its homologs in diploid model plants (AtCRY2 and SlCRY2). Quantitative RT-PCR analysis of the FaCRY2 showed the highest expression level in the leaf and flower tissues. The subcellular localization results indicate that the FaCRY2 was a nucleus-localized protein. The cry2 mutants, silenced by artificial micro-interfering RNA interference (AmiRNAi) using 'Benihoppe' strawberry as genetic background, showed a growth retardation, including dwarf phenotype, decreased free IAA content, delayed flowering time, deepened the lignification degree of petiole cells, decreased stomatal conductance and transpiration rate. RNA-seq analysis showed that there were 910 significantly differentially expressed genes (DEGs) between wild-type (WT) and cry2. They were mainly enriched in hormone regulation, cell development and stress response, etc. The decrease of IAA accumulation could be the main factor responsible for the delayed growth of cry2. Taken together, our results suggested the complex roles of FaCRY2 in the plant growth regulation in cultivated strawberry.

Comprehensive transcriptome analysis unravels the crucial genes during adventitious root development induced by carbon monoxide in Cucumis sativus L.

Carbon monoxide (CO) has been reported to be participated in adventitious rooting. However, knowledge about the interrelationship between CO and phytohormones during rooting is obscure. The molecular mechanism of CO-induced rooting is currently unclear. The roles of CO in adventitious rooting in Cucumis sativus L. at the transcriptional level were investigated. The results show that 10μM hematin (a CO donor) has a significant positive effect on adventitious rooting in cucumber. A total of 1792 differentially expressed genes (DEGs; 1103 up-regulated and 689 down-regulated) were identified in hematin treatment by RNA sequencing analysis. There were 37, 18 and 19 DEGs significantly enriched in plant hormone signal transduction, sucrose and starch metabolism, and phenylalanine metabolism, respectively. Both transcriptome and real-time quantitative PCR results showed that the expressions of AUX22D, IAA6, SAUR21, SAUR24, GH3.5, CYCD3-3, TIFY10a, TIFY10A and TIF9 promoted the accumulation of IAA, BR, JA and SA in plant hormone signal transduction. The up-regulation of HK3, TPPF, otsB, TPS7, TPS9 and the down-regulation of AGPS1, AGPS3 increased the content of starch and total sugar by mediating the activity of some critical enzymes, including HK, TPS, TPP and AGP. PER47, PER61, PER24, PER66, PER4 and CCR2 increased the lignin content. Our results suggest that CO could promote the accumulation of plant hormones, starch, sugar and lignin during adventitious rooting by regulating the expression of some related genes, including AUX22D, IAA6, SAUR21, SAUR24, GH3.5, CYCD3-3, TIFY10a, TIFY10A, TIF9 HK3, otsB, TPS7, TPS9, AGPS1, AGPS3, PER47, PER61, PER24, PER66, PER4, and CCR2. Thus, we provides an interesting candidate gene list for further studies on the molecular mechanisms of adventitious rooting.

Melatonin enhances the low-temperature combined low-light tolerance of pepper (Capsicum annuum L.) seedlings by regulating photosynthesis, carotenoid, and hormone metabolism

Low temperature combined with low light (LL) is severe abiotic stress to plant growth and yield. However, little is known about the physiological mechanisms of the melatonin (MT) involved in the adaptation of pepper ( Capsicum annuum L.) to LL. In this study, pepper seedlings subjected to LL stress (15 ℃/5 ℃, 100 µmol photons m −2 s −1 ) were pre-sprayed with 200 µmol L −1 MT to investigate the protective role of MT in photosynthesis, carotenoid metabolism, as well as hormones of pepper ( Capsicum annuum L.) seedling. Our results indicated that the application of exogenous MT reduced the negative effect on plant growth inhibition of pepper seedlings caused by LL stress, significantly increased chlorophyll contents and photosynthetic capacity as result of improved photosynthesis rate, upregulated the relative expressions of PSΠ reaction center proteins genes ( CaPsb A , CaPsb B , CaPsb C , and CaPsb S ), reduced NPQ, 1-qP, and qN, as well as increased Fv/Fm, qP, Y(Ⅱ), and electron transport rate (ETR) after 7 days. In addition, MT significantly enhanced abscisic acid metabolism and biosynthesis of indoleacetic acid, gibberellin 3, and zeatin-type cytokinins after 6 h, 12 h, 24 h, 48 h, and 168 h. Markedly, MT increased the contents of zeaxanthin, which is induced by the down-regulation of CaZEP , by 149.55%. Our findings confirmed the mitigating potential of MT application for LL stress by maintaining plant growth, improving the photosynthetic characteristics, regulating carotenoids, and hormone metabolism. • Melatonin mitigates LL-induced stress in pepper by maintaining normal morphology and photosynthesis. • Melatonin alleviates LL-induced stress mediated by regulating relative expressions of psb A, psb B, psb C , and psb S . • Melatonin alleviates LL-induced stress mediated by enhancing zeaxanthin contents induced by downregulation of CaZEP . • Melatonin alleviates LL-induced stress mediated by significantly increasing GA3, IAA, and ZT accumulation while decrease ABA.

MdATG5a positively regulates nitrogen uptake under low nitrogen conditions by enhancing the accumulation of flavonoids and auxin in apple roots

Nitrogen (N) deficiency limits the production of apple ( Malus domestica ) on the Loess Plateau, which is the largest apple-producing region in China. Autophagy is a conserved degradation and recycling pathway in eukaryotes that has been reported to play a key role in the responses of plants to N deficiency. We previously identified the core autophagy-related gene MdATG5a from apple and showed that overexpression of this gene improves the drought tolerance of apple plants. Here, we showed that MdATG5a overexpression enhances root growth and the root N uptake of apple plants under low-N conditions and contributes to improving N use efficiency. MdATG5a positively regulated root N uptake by activating the shikimate pathway to increase levels of phenylalanine and tryptophan, which promoted the accumulation of flavonoids and IAA in apple roots under low-N conditions. In addition, MdATG5a was demonstrated to affect the expression of genes involved in root development in response to N deficiency. Moreover, we also found that autophagy activity was higher in the roots of MdATG5a -overexpressing apple plants compared with wild-type plants under low-N conditions. Overall, the results of our study provide new insights into the association between MdATG5a -mediated autophagy and the root N uptake of apple plants under low-N conditions. • MdATG5a overexpression improved nitrogen usage in apple under low-N conditions. • MdATG5a positively regulated root N uptake in apple under low-N stress. • MdATG5a promoted the flavonoids accumulation in apple roots under low-N stress. • MdATG5a increased the IAA level in apple roots under low-N stress.

Impairment of root auxin-cytokinins homeostasis induces collapse of incompatible melon grafts during fruit ripening.

The factors underlying the plant collapse of certain melon-pumpkin graft combinations are not fully understood. Our working hypothesis was that impairment of photoassimilates transport in incompatible combinations induces an imbalance in the homeostasis of root auxin (indole-3-acetic acid; IAA) and of cytokinins, probably triggering plant collapse. Root IAA and cytokinins levels in the presence and absence of fruit and changes in root and scion metabolites were investigated in compatible and incompatible combinations. We showed elevated levels of IAA, 2-oxoindole-3-acetic acid (IAA catabolite), indole-3-acetylaspartate (IAA conjugate), and cis-zeatin-type cytokinins, but low levels of trans-zeatin-type cytokinins in the roots of plants of the incompatible combination during fruit ripening. Similarly, during fruit ripening, the expression of the YUCCA genes, YUC2, YUC6, and YUC11 (required for auxin biosynthesis), the GRETCHEN-HAGEN3 gene (required for auxin conjugation), and the cytokinin oxidase/dehydrogenase 7 (CKX7) gene (regulates the irreversible degradation of cytokinin) was enhanced in the roots of plants of the incompatible combination. Moreover, in the incompatible combination the fruiting process restricted transport of photoassimilates to the rootstock and induces their accumulation in the scion. In addition, high levels of hydrogen peroxide and malondialdehyde and reduced activity of antioxidant enzymes were observed in the roots of the incompatible graft. Our results showed that the collapse of the incompatible graft combination during fruit ripening is closely associated with a dramatic accumulation of IAA in the roots, which probably elicits oxidative damage and disturbs the balance of IAA and cytokinins that is of critical importance in melon-pumpkin graft compatibility.

Nitrogen limits zinc‐mediated stimulation of tillering in rice by modifying phytohormone balance under low‐temperature stress

AbstractZinc (Zn) can improve resistance of rice plants to abiotic stress and promote the recovery of rice tillers by influencing auxin (IAA) synthesis, Zn absorption is closely related to nitrogen (N) concentrations; however, the mechanisms by which Zn regulates rice tiller recovery at low temperatures under different N levels are rarely studied. In this study, a solution culture experiment was conducted at two temperatures, three different Zn concentrations, and two N concentrations. Low temperature during the vegetative stage damaged the rice antioxidant system, suppressed nutrient uptake, and decreased the number of tillers. Increasing Zn application improved the resistance of rice plants to low‐temperature stress under normal N levels, enhanced nutrient absorption, improved tiller bud cytokinin (CTK) concentrations, and the CTK/IAA ratio, which accelerated tiller recovery relative to plants receiving standard Zn treatment. Shoot Zn concentrations were positively correlated with tiller numbers at normal N levels. High N attenuated the positive effect of Zn on rice tillering at low temperatures due to higher shoot Zn and IAA accumulation, and lower tiller buds CTK/IAA ratios. However, appropriate Zn application under high N levels was conducive to breaking tiller dormancy and promoting tillering growth spurts when recovering to normal temperature, which was related to the synergistic regulation of hormone balance and nutrient absorption by N and Zn. In conclusion, Zn could enhance rice low‐temperature stress resilience and facilitate tiller recovery via balancing the hormones in tiller buds. However, higher environmental N limited the stimulation of Zn on rice tillering under low temperature.