IAA Biosynthesis Research Articles

Profiles of endogenous ABA, bioactive GAs, IAA and their metabolites in Medicago truncatula Gaertn. non-embryogenic and embryogenic tissues during induction phase in relation to somatic embryo formation

Main conclusionDuring the 3-week-long induction phase, when M. truncatula cells leaf explants from non-embryogenic genotype (M9) and embryogenic variant (M9-10a) were forming the callus, biosynthesis and degradation of ABA, Gas and IAA proceeded at different levels. Induction of embryo formation is related to a lower ABA content, compared to the content of IAA and that of total bioactive GAs.Endogenous phytohormones are involved in the regulation of zygotic embryogenesis, but their role, especially of ABA, a plant growth inhibitor, in inducing somatic embryogenesis (SE) in angiosperms is still incompletely known. To arrive a better understanding of the ABA role in the process, we analyzed simultaneously and in detail changes in the contents of both ABA and five bioactive GAs (GA4, GA7, GA1, GA3, GA6) and IAA in M. truncatula non-embryogenic M9 (NE) and embryogenic M9-10a (E) genotypes. The initial leaf explants of both genotypes, and particularly NE, contained many times more ABA compared to the total bioactive GAs or IAA. In tissues during the entire 21-day induction all the hormones mentioned and their metabolites or conjugates were present; however, their contents were found to differ between the lines tested. The ABA level in primary explants of NE genotype was more than two times higher than that in E genotype. An even larger difference in the ABA content was found on the last day (day 21) of the induction phase (IP); the ABA content in E callus was over six times lower than in NE callus. In contrast, the IAA and GAs contents in primary explants of both genotypes in relation to ABA were low, but the contents of IAA and GAs exceeded that of ABA in the M9-10a tissues on the last day of IP. It is shown for the first time that endogenous ABA together with endogenous bioactive GAs and IAA is involved in acquisition of embryogenic competence in Medicago truncatula leaf somatic cells. These findings have a strong functional implication as they allow to improve the SE induction protocol.

Unveiling the putative functional genes present in root-associated endophytic microbiome from maize plant using the shotgun approach.

To ensure food security for the ever-increasing world's population, it is important to explore other alternatives for enhancing plant productivity. This study is aimed at identifying the putative plant growth-promoting (PGP) and endophytic gene clusters in root-associated endophytic microbes from maize root and to also verify if their abundance is affected by different farming practices. To achieve this, we characterize endophytic microbiome genes involved in PGP and endophytic lifestyle inside maize root using the shotgun metagenomic approach. Our results revealed the presence of genes involved in PGP activities such as nitrogen fixation, HCN biosynthesis, siderophore, 4-hydroxybenzoate, ACC deaminase, phenazine, phosphate solubilization, butanediol, methanol utilization, acetoin, nitrogen metabolism, and IAA biosynthesis. We also identify genes involved in stress resistance such as glutathione, catalase, and peroxidase. Our results further revealed the presence of putative genes involved in endophytic behaviors such as aerotaxis, regulator proteins, motility mechanisms, flagellum biosynthesis, nitrogen regulation, regulation of carbon storage, formation of biofilm, reduction of nitric oxide, regulation of beta-lactamase resistance, type III secretion, type IV conjugal DNA, type I pilus assembly, phosphotransferase system (PTS), and ATP-binding cassette (ABC). Our study suggests a high possibility in the utilization of endophytic microbial community for plant growth promotion, biocontrol activities, and stress mitigation. Further studies in ascertaining this claim through culturing of the beneficial isolates as well as pot and field experiments are necessary.

Influence of cultivation conditions on IAA - producing activity of endophytic bacterial strains isolated from morning-glory (IPOMOEA PES-CAPRAE(L.) R.Br.)

This work presents the experimental study results of the influence of the culture medium on the ability to IAA synthesis of three endophytic strains TH10R, TH11T, and TH13T from roots of Ipomoea pes-caprae. Three investigated strains give the highest IAA concentration after 96 h of cultivation. A significant increase in IAA biosynthesis was obtained by cultivating the TH10R strain in a medium containing lactose or starch as a carbon source and NH4Cl or KNO3 as a nitrogen source. The TH11T strain produces the maximum amount of IAA, using glucose or xylose and KNO3 or NH4NO3 as carbon and nitrogen sources, respectively. Sucrose is a suitable carbon source for the TH13T strain; on a sucrose-containing medium, the TH13T strain produces the highest IAA amount. The most active strain is TH10R, identified as Bacillus mycoides and named Bacillus mycoides TH10R.

Acetic acid mitigated salt stress by alleviating ionic and oxidative damages and regulating hormone metabolism in perennial ryegrass (<i>Lolium perenne</i> L.)

Organic chemical priming is an effective strategy in mitigating salt stress to plants. The objective of this study was to determine effects and associated mechanisms of acetic acid regulating plant tolerance to salt stress. Perennial ryegrass plants were pre-treated with 20 mM acetic acid and subsequently subjected to salt stress for 28 days. Salt stress caused increased endogenous acetic acid content with up-regulated expression of its key biosynthetic gene <i>LpPDC1</i>. Application of acetic acid effectively alleviated salt caused damage in perennial ryegrass. Acetic acid treatment increased K⁺ content and suppressed Na⁺ accumulation to maintain a higher K⁺/Na⁺ ratio in leaves exposed to salt stress. Plants treated with acetic acid also had significantly lower levels of <inline-formula> <tex-math id="Z-20210219143604">${\rm O}_2^- $</tex-math> <alternatives> <graphic xmlns:xlink="http://www.w3.org/1999/xlink" href="GR-2021-0003_Z-20210219143604.jpg"/> <graphic xmlns:xlink="http://www.w3.org/1999/xlink" href="GR-2021-0003_Z-20210219143604.png"/> </alternatives> </inline-formula> and H₂O₂, but higher SOD and CAT activities than those of the control after 21 days of salt stress. Acetic acid treatment also altered the plants endogenous phytohormone content with higher content of jasmonate (including JA, JA-ILe, and cis-OPDA), auxin (IAA), and cytokinins (CK, such as tZ, cZR, and iP), but lower content of abscisic acid (ABA) under salt stress conditions. Furthermore, expression of genes involved in JA, IAA, and CK biosynthesis and signaling pathways were up-regulated, while those involved in ABA were down-regulated by acetic acid treatment under salt stress. The results demonstrate that acetic acid could mitigate salt stress in perennial ryegrass by regulating K⁺ and Na⁺ balance, promoting ROS scavenging, and activating stress-protection hormone synthesis and signaling.

Expression of key auxin biosynthesis genes correlates with auxin and starch content of developing wheat (Triticum aestivum) grains.

The effect of auxin on wheat (Triticum aestivum L.) grain size is contentious. Additionally, the contributions to the IAA pool from de novo synthesis versus hydrolysis of IAA-glucose are unclear. Here, we describe the first comprehensive study of tryptophan aminotransferase and indole-3-pyruvate mono-oxygenase expression from 5 to 20 days after anthesis. A comparison of expression data with measurements of endogenous IAA via combined liquid chromatography-tandem mass spectrometry using heavy isotope labelled internal standards indicates that TaTAR2-B3, TaYUC9-A1, TaYUC9-B, TaYUC9-D1, TaYUC10-A and TaYUC10-D are primarily responsible for IAA production in developing grains. Furthermore, these genes are expressed specifically in developing grains, like those found in rice (Oryza sativa L.) and maize (Zea mays L.). Our results cast doubt on the proposed role of THOUSAND-GRAIN WEIGHT gene, TaTGW6, in promoting larger grain size via negative effects on grain IAA content. Work on this gene overlooked the contribution of IAA biosynthesis from tryptophan. Although IAA synthesis occurs primarily in the endosperm, we show the TaYUC9-1 group is also strongly expressed in the embryo. Within the endosperm, TaYUC9-1 expression is highest in aleurone and transfer cells, suggesting that IAA has a key role in differentiation of these tissues as has been proposed for other cereals.

Characterization and synthesis of indole-3-acetic acid in plant growth promoting Enterobacter sp.

Indole-3-acetic acid (IAA) plays an important role in the growth and development of plants. In this study, a series of predominant strains were isolated and identified as Enterobacter sp. with remarkable IAA-producing capabilities. The IAA-producing strains are mainly tryptophan-dependent and have significantly high yields of IAA (3477 μg mL−1 and 3378 μg mL−1). The ipdC gene encoding indole-3-pyruvate decarboxylase was identified by genomic analysis and RT-qPCR analysis, indicating the involvement of the indole-3-pyruvic acid (IPyA) pathway of IAA biosynthesis. The IPyA pathway was also confirmed by the intermediate assay. The IAA product of microbial metabolites was isolated, purified and characterized. These microbes exhibiting IAA production significantly promoted the growth of maize, increasing root length, plant height, fresh weight and dry weight. Thus, Enterobacter sp. with high IAA production has great prospects in agricultural and industrial applications.

Downregulation of the photosynthetic machinery and carbon storage signaling pathways mediate La2O3 nanoparticle toxicity on radish taproot formation

The molecular and physiological mechanisms of how rare earth oxide nanoparticles (NPs) alter radish (Raphanus sativus L.) taproot formation and cracking were investigated in the present study. We compared plants that received suspensions of 10, 50, 100, 300 mg L−1 of La2O3 NPs, 300 m L−1 La2O3 bulk-particles (BPs), 0.8 m L−1 La3+, or only water for six days during their tuber formation period. 100 and 300 mg L−1 La2O3 NPs exposure decreased storage root biomass by 38% and 60%, respectively, and they both induced visible root cracking. Physiological analyses showed that La2O3 NPs exposure (>100 mg L−1) significantly inhibited leaf net photosynthetic rate, cell wall pectin synthesis of both storage root epidermis and xylem parenchyma tissues, but increased the contents of cellulose and hemicellulose 1 in root epidermis cell walls. Moreover, transcriptome analysis further found that La2O3 NPs changed root cell wall structure by down-regulating core genes involved in cell wall pectin and IAA biosynthesis, which coincided with the observed La2O3 NPs-induced root cracking. Our results revealed the molecular mechanisms related to cell wall carbohydrate metabolism in response to NPs stress, providing a step forward for understanding the causes of NPs phytotoxicity on edible plant taproot formation and cracking.

Physiological and molecular responses of the root system of indica–japonica intersubspecific tetraploid rice seedlings to ion beam stress

Low-energy ion beam bombardment can induce various biological effects on plants, including stimulation, damage, and mutation. However, the physiological and molecular mechanisms of the stress effects of indica–japonica intersubspecific tetraploid rice seedlings roots in response to ion implantation are not fully understood. In this work, indica–japonica intersubspecific tetraploid rice seeds were implanted with different doses of ion beam to explore the responses of their seedling roots. The investigation found that that high-dose ion implantation significantly reduced the total root length, root surface area, total root volume and root tips number, significantly increased MDA content in roots, and interfered with the expression level of IAA biosynthesis and transport related genes. Under low-dose radiation, the antioxidant enzyme activity in the roots of intersubspecific tetraploid rice increased significantly compared with the control, and remained at a high level during 5–15 days of culture, without significant change. Meanwhile, the expression of IAA biosynthesis and transportation related genes were up-regulated, and the IAA content was significantly increased, which was 20.12% higher than that of the control, which finally made the root activity significantly higher than that of the parents. The aforementioned results will be useful for further research on the physiological and molecular mechanisms of indica–japonica intersubspecific tetraploid rice seedlings roots to ion beam stress.

Melatonin promotes adventitious root formation in apple by promoting the function of MdWOX11

BackgroundMelatonin (MT) is important for plant growth and development; however, it is not known whether MT is involved in apple adventitious root (AR) development. In this study, we treated Malus prunifolia (MP) at four different stages of AR development, and analyzed the level of the endogenous hormones MT, auxin (IAA), zeatin-riboside (ZR), abscisic acid (ABA), and gibberellins (GA1 + 3) in all four treatment groups and the untreated control group. The expression of MT, IAA biosynthesis, transport and signal transduction, the cell cycle, and root development related genes were quantified by RT-qPCR. The function of MdWOX11 was analyzed in transgenic apple plants.ResultsThe promotion of AR development by MT was dependent on the stage of AR induction between 0 and 2 d in apple rootstocks. MT-treatment increased the level of IAA and crosstalk existed between MT and IAA during AR formation. The expression of MdWOX11 was induced by MT treatment and positively regulated AR formation in apple. Furthermore, transgenic lines that overexpressed MdWOX11 lines produced more ARs than ‘GL3’. Phenotypic analysis indicated that MdWOX11 overexpression lines were more sensitive to exogenous MT treatment than ‘GL3’, suggesting that MdWOX11 regulates AR formation in response to MT in apple rootstock.ConclusionsMT promotes AR formation mainly during the AR induction stage by inducing IAA levels and upregulating MdWOX11.

Plant growth promoting potential of bacterial endophytes from three terrestrial mediterranean orchid species

Orchids are highly dependent on symbiotic microorganisms during their entire life cycle. Whereas an important role in orchid seed germination and early plant development is well established for mycorrhizal fungi, the influence of endophytic bacteria on orchid growth has been less investigated. Here, we report the isolation of endophytic bacteria from different organs of three terrestrial Mediterranean orchid species (Spiranthes spiralis, Serapias vomeracea and Neottia ovata), the investigation of their potential Plant Growth-Promoting (PGP) traits and their interaction with the orchid mycorrhizal (OM) fungus Tulasnella calospora in vitro. Little overlap was found among endophytic bacteria isolated from the different organs of the three orchid species. Taxonomic identification, based on the 16S rRNA gene, of fifty dereplicated bacterial isolates revealed that they belong to the genera Pseudomonas, Pantoea, Rahnella, Staphylococcus, Sphingomonas, Microbacterium, Streptomyces, Fictibacillus and Bacillus. Most bacterial isolates exhibited some potential PGP traits, such as nutrient solubilization, ACC deaminase activities and/or IAA biosynthesis. Although some Pseudomonas reduced growth of the OM fungus Tulasnella calospora, most isolates did not affect fungal growth. These results increase our understanding of the diversity and potential PGP functions of bacterial endophytes in terrestrial orchids, and suggest a role as beneficial partners in the orchid microbiota.

Weeping candidate genes screened using comparative transcriptomic analysis of weeping and upright progeny in an F1 population of Prunus mume.

Weeping is a specific plant architecture with high ornamental value. Despite the considerable importance of the weeping habit to landscaping applications and knowledge of plant architecture biology, little is known regarding the underlying molecular mechanisms. In this study, growth and phytohormone content were analyzed among the progeny of different branch types in an F1 mapping population of Prunus mume with varying plant architecture. Bulked segregant RNA sequencing was conducted to compare differences among progeny at a transcriptional level. The weeping habit appears to be a complex process regulated by a series of metabolic pathways, with photosynthesis and flavonoid biosynthesis highly enriched in differentially expressed genes between weeping and upright progeny. Based on functional annotation and homologous analyses, we identified 30 candidate genes related to weeping that merit further analysis, including 10 genes related to IAA and GA3 biosynthesis, together with 6 genes related to secondary branch growth. The results of this study will facilitate further studies of the molecular mechanisms underlying the weeping habit in P. mume.

Indole-3-acetic acid biosynthesis and its regulation in plant-associated bacteria.

Numerous studies have reported the stimulation of plant growth following inoculation with an IAA-producing PGPB. However, the specific mode of IAA production by the PGPB is rarely elucidated. In part, this is due to the overwhelming complexity of IAA biosynthesis and regulation. The promiscuity of the enzymes implicated in IAA biosynthesis adds another element of complexity when attempting to decipher their role in IAA biosynthesis. To date, the majority of research on IAA biosynthesis describes three separate pathways classified in terms of their intermediates-indole acetonitrile (IAN), indole acetamide (IAM), and indole pyruvic acid (IPA). Each of these pathways is mediated by a set of enzymes, many of which are traditionally assumed to exist for that specific catalytic role. This lends the possibility of missing other, novel, enzymes that may also incidentally serve that function. Some of these pathways are constitutively expressed, while others are inducible. Some enzymes involved in IAA biosynthesis are known to be regulated by IAA or by IAA precursors, as well as by a multitude of environmental cues. This review aims to provide an update to our current understanding of the biosynthesis and regulation of IAA in bacteria. KEY POINTS: • IAA produced by PGPB improves bacterial stress tolerance and promotes plant growth. • Bacterial IAA biosynthesis is convoluted; multiple interdependent pathways. • Biosynthesis of IAA is regulated by IAA, IAA-precursors, and environmental factors.

Co-Inoculation of Bacillus velezensis Strain S141 and Bradyrhizobium Strains Promotes Nodule Growth and Nitrogen Fixation.

The objective of this research was to evaluate the PGPR effect on nodulation and nitrogen-fixing efficiency of soybean (Glycine max (L.) Merr.) by co-inoculation with Bradyrhizobium diazoefficiens USDA110. Co-inoculation of Bacillus velezensis S141 with USDA110 into soybean resulted in enhanced nodulation and N2-fixing efficiency by producing larger nodules. To understand the role of S141 on soybean and USDA110 symbiosis, putative genes related to IAA biosynthesis were disrupted, suggesting that co-inoculation of USDA110 with S141ΔyhcX reduces the number of large size nodules. It was revealed that yhcX may play a major role in IAA biosynthesis in S141 as well as provide a major impact on soybean growth promotion. The disruption of genes related to cytokinin biosynthesis and co-inoculation of USDA110 with S141ΔIPI reduced the number of very large size nodules, and it appears that IPI might play an important role in nodule size of soybean–Bradyrhizobium symbiosis. However, it was possible that not only IAA and cytokinin but also some other substances secreted from S141 facilitate Bradyrhizobium to trigger bigger nodule formation, resulting in enhanced N2-fixation. Therefore, the ability of S141 with Bradyrhizobium co-inoculation to enhance soybean N2-fixation strategy could be further developed for supreme soybean inoculants.

Hsp40 Protein LeDnaJ07 Enhances the Thermotolerance of Lentinula edodes and Regulates IAA Biosynthesis by Interacting LetrpE.

Our previous study found that LeDnaJ07 RNAi decreased Lentinula edodes resistance to heat stress and Trichoderma atroviride infection. In this study, the structure and function of the LeDnaJ07 gene was analyzed by gene cloning and overexpression in L. edodes stress-sensitive strain YS55 via the Agrobacterium-mediated transformation method. Transformants were confirmed by qRT-PCR, fluorescence observation and Southern blotting. Overexpression of LeDnaJ07 in YS55 not only enhanced L. edodes mycelial resistance to heat stress but also facilitated mycelial growth. In the presence of heat stress, the intracellular IAA content showed a significant increase in the two LeDnaJ07 overexpression strains but only a slight change in the YS55 wild type strain. Moreover, the interaction between LeDnaJ07 and LetrpE was demonstrated via Y2H and BiFC assays. These results suggested that LeDnaJ07 may be involved in regulating IAA biosynthesis and the resistance of L. edodes to heat stresses via interacting with LetrpE.

TPST is involved in fructose regulation of primary root growth in Arabidopsis thaliana.

TPST is involved in fructose signaling to regulate the root development and expression of genes in biological processes including auxin biosynthesis and accumulation in Arabidopsis. Sulfonation of proteins by tyrosine protein sulfotransferases (TPST) has been implicated in many important biological processes in eukaryotic organisms. Arabidopsis possesses a single TPST gene and its role in auxin homeostasis and root development has been reported. Here we show that the Arabidopsis tpst mutants are hypersensitive to fructose. In contrast to sucrose and glucose, fructose represses primary root growth of various ecotypes of Arabidopsis at low concentrations. RNA-seq analysis identified 636 differentially expressed genes (DEGs) in Col-0 seedlings in response to fructose verses glucose. GO and KEGG analyses of the DEGs revealed that fructose down-regulates genes involved in photosynthesis, glucosinolate biosynthesis and IAA biosynthesis, but up-regulates genes involved in the degradation of branched amino acids, sucrose starvation response, and dark response. The fructose responsive DEGs in the tpst mutant largely overlapped with that in Col-0, and most DEGs in tpst displayed larger changes than in Col-0. Interestingly, the fructose up-regulated DEGs includes genes encoding two AtTPST substrate proteins, Phytosulfokine 2 (PSK2) and Root Meristem Growth Factor 7 (RGF7). Synthesized peptides of PSK-α and RGF7 could restore the fructose hypersensitivity of tpst mutant plants. Furthermore, auxin distribution and accumulation at the root tip were affected by fructose and the tpst mutation. Our findings suggest that fructose serves as a signal to regulate the expression of genes involved in various biological processes including auxin biosynthesis and accumulation, and that modulation of auxin accumulation and distribution in roots by fructose might be partly mediated by the TPST substrate genes PSK-α and RGF7.

Transcriptome profiling provides insights into molecular mechanism in Peanut semi-dwarf mutant

BackgroundPlant height, mainly decided by main stem height, is the major agronomic trait and closely correlated to crop yield. A number of studies had been conducted on model plants and crops to understand the molecular and genetic basis of plant height. However, little is known on the molecular mechanisms of peanut main stem height.ResultsIn this study, a semi-dwarf peanut mutant was identified from 60Co γ-ray induced mutant population and designated as semi-dwarf mutant 2 (sdm2). The height of sdm2 was only 59.3% of its wild line Fenghua 1 (FH1) at the mature stage. The sdm2 has less internode number and short internode length to compare with FH1. Gene expression profiles of stem and leaf from both sdm2 and FH1 were analyzed using high throughput RNA sequencing. The differentially expressed genes (DEGs) were involved in hormone biosynthesis and signaling pathways, cell wall synthetic and metabolic pathways. BR, GA and IAA biosynthesis and signal transduction pathways were significantly enriched. The expression of several genes in BR biosynthesis and signaling were found to be significantly down-regulated in sdm2 as compared to FH1. Many transcription factors encoding genes were identified as DEGs.ConclusionsA large number of genes were found differentially expressed between sdm2 and FH1. These results provide useful information for uncovering the molecular mechanism regulating peanut stem height. It could facilitate identification of causal genes for breeding peanut varieties with semi-dwarf phenotype.

Molecular imprints of plant beneficial Streptomyces sp. AC30 and AC40 reveal differential capabilities and strategies to counter environmental stresses

Streptomyces and their biomolecules are well explored for antibiotics production, bioremediation and alleviating the plant stresses due to their plant beneficial attributes. Therefore, due to plethora of biological attributes, the accurate portraying of molecular capabilities of these microorganisms at genomic level is of paramount importance. Here, we have evaluated biochemical attributes of two Streptomyces sp. AC30and AC40 for different plant beneficial activities which are antagonistic to Fusarium oxysporum, Alternaria solani, Sclerotinia sclerotium and Phytopthora infestans. In parallel, the draft genomes of these strains were deduced to understand their genomic capabilities using Illumina platform. The complete genome of AC30and AC40 were 11,284,599 bp and 12,636,188 bp in size with total G + C content of 62.36 and 54.75 %, respectively. Overall, higher number of genes (14,024) was reported for AC40 as compared to AC30 (12,476). The comparative genome organization revealed sharing of a few biosynthetic clusters as well as some exclusive biosynthetic clusters among both the strains. Further, expansion in the chitinases and glucanases was found in the genome of AC40. In addition, genes for 3-phytase and glycosyl hydrolase family 19 were restricted to AC40 only. The comparative genome study revealed presence of plant induced nitrilase in AC40 which is predicted for its role in IAA biosynthesis, release of ammonia, biotransformation of nitrile compounds to corresponding acids and bioremediation of soil containing nitrile compounds. For IAA and secondary metabolites biosynthesis, flavin-dependent monooxygenase, a rate limiting factor in Trp-dependent auxin biosynthesis pathway was found exclusive to AC30 genome. The comparative study revealed the diversification of few pathways/strategies to suppress plant pathogens and promote plant growth by Streptomyces strains.

Disruption of &lt;i&gt;CYCLOPHILIN 38&lt;/i&gt; Function Reveals a Photosynthesis-Dependent Systemic Signal Controlling Lateral Root Emergence

Photosynthesis in leaves generates the fixed-carbon resources and essential metabolites that support sink tissues, such as roots. One of these products, sucrose, is known to promote primary root growth, but it is not clear what other molecules may be involved and whether other stages of root system development are affected by photosynthate levels. Through a mutant screen to identify pathways regulating root system architecture, we identified a mutation in the CYCLOPHILIN 38 (CYP38) gene, which causes an accumulation of pre-emergent stage lateral roots, with a minor effect on primary root growth. CYP38 was previously reported to maintain the stability of Photosystem II (PSII) in chloroplasts. CYP38 expression is enriched in the shoot and grafting experiments show that the gene acts non-cell autonomously to promote lateral root emergence. Growth of wild-type plants under low light conditions phenocopied the cyp38 lateral root emergence phenotype as did the inhibition of PSII-dependent electron transport or NADPH production. Importantly, the cyp38 root phenotype is not rescued by exogenous sucrose, suggesting the involvement of another metabolite. Auxin (IAA) is an essential hormone promoting root growth and its biosynthesis from tryptophan is dependent on reductant generated during photosynthesis. Both WT seedlings grown under low light and cyp38 mutants have highly diminished levels of IAA in root tissues. The cyp38 lateral root defect is rescued by IAA treatment, revealing that photosynthesis promotes lateral root emergence partly through IAA biosynthesis. Metabolomic profiling shows that the accumulation of several defense-related metabolites are also photosynthesis-dependent, suggesting that the regulation of a number of energy-intensive pathways are down-regulated when light becomes limiting.

Hydrogen-rich water promotes elongation of hypocotyls and roots in plants through mediating the level of endogenous gibberellin and auxin.

The aim of this study was to investigate effects of the hydrogen-rich water (HRW) on the vegetable growth, and explore the possibility of applying HRW for protected cultivation of vegetables. Results showed that compared with control, HRW treatment significantly promoted fresh weight, hypocotyl length and root length of mung bean seedlings. The strongest stimulation was observed for 480 μM H2 (60% of saturated HRW concentration) treatment. This concentration was used in the following experiments. The enhanced cell elongation was correlated with the changes in the level of endogenous phytohormones. In the dark-grown hypocotyls and roots of mung bean seedlings, HRW significantly increased the content of IAA and GA3. Addition of GA3 enhanced the hypocotyl elongation only. uniconazole, an inhibitor of GA3 biosynthesis, inhibited HRW-induced hypocotyl elongation, but did not affect root elongation. Exogenous application of IAA promoted HRW effects on elongation of both the hypocotyl and the root, while the IAA biosynthesis inhibitor TIBA negated the above affects. The general nature of HRW-induced growth-promoting effects was further confirmed in experiments involving cucumber and radish seedlings. Taken together, HRW treatment promoted growth of seedlings, by stimulating elongation of hypocotyl and root cells, via HRW-induced increase in GA and IAA content in the hypocotyl and the root respectively.

Molecular, cellular and Yin-Yang regulation of grain size and number in rice

Final grain size and grain number per plant, representing the sink capacity, are two major developmental traits determining grain yield of rice and other cereals. Understanding the regulatory mechanisms controlling grain size and number has become an important research field in plant science. Grain number and size are determined by the activity, size and number of inflorescence meristems, branch meristems and floral meristems, which are coordinately regulated by both rate and duration of cell division, cell expansion and cell differentiation. Current advances have revealed several signaling pathways controlling grain size and number, including G protein signaling, biosynthesis and signaling of BR, CK and IAA, MAPK signaling, peptide signaling, the ubiquitin-proteasome degradation pathway, epigenetic pathways and transcriptional regulation. This review provides a general overview of recent findings and future perspectives in molecular, cellular and Yin-Yang regulatory mechanisms of coordinating grain size and number in rice, which has substantial implications for breaking the yield bottleneck caused by the trade-off of grain size and number in crop genetic improvement. We also propose 16 key scientific questions underlying grain size and number in rice and other crops to call for an international coordinated effort in studying and solving these problems in the form of a project named GSGN16.