Brassinosteroids is involved in methane-induced adventitious root formation via inducing cell wall relaxation in marigold

Insight into saffron associated microbiota from different origins and explore the endophytes for enhancement of bioactive compounds

Crocus sativus L. is a perennial crop for its valuable active compounds. Plant-associated microbes impact on the quality and efficacy of medicinal herbs by promoting bioactive components accumulation. However, how microbes influence the accumulation of bioactive components in saffron have not been well studied. Here, the microbiome in C. sativus derived from 3 core production areas were deciphered by 16S rDNA sequencing and the relationship between endophytes and bioactive ingredients were further investigated. The main results are as follows: (1) Both Comamonadaceae and Burkholderiaceae were positively correlated with the content of bioactive components in the stigmas. (2) The synthesis of crocin was positively correlated with Xanthomonadaceae, negatively correlated with Lachnospiraceae and Prevotellaceae. Therefore, further investigation is required to determine whether Xanthomonadaceae plays an unknown function in the synthesis of crocin. These findings provide guidelines for disentangling the function of endophytes in the production of bioactive ingredients and thus for microbe-mediated breeding.

Genome-wide characterization of the xyloglucan endotransglucosylase/hydrolase family genes and their response to plant hormone in sugar beet

Xyloglucan endotransglucosylase/hydrolases (XTHs) play a crucial role in plant growth and development. However, their functional response to phytohormone in sugar beet still remains obscure. In this study, we identified 30 putative BvXTH genes in the sugar beet genome. Phylogenetic and evolutionary relationship analysis revealed that they were clustered into three groups and have gone through eight tandem duplication events under purifying selection. Gene structure and motif composition analysis demonstrated that they were highly conserved and all contained one conserved glycoside hydrolase family 16 domain (Glyco_hydro_16) and one xyloglucan endotransglycosylase C-terminus (XET_C) domain. Transcriptional expression analysis exhibited that all BvXTHs were ubiquitously expressed in leaves, root hairs and tuberous roots, and most of them were up-regulated by brassinolide (BR), jasmonic acid (JA), abscisic acid (ABA) and gibberellic acid (GA3). Further mutant complementary experiment demonstrated that expression of BvXTH17 rescued the retarded growth phenotype of xth22, an Arabidopsis knock out mutant of AtXTH22. The findings in our work provide fundamental information on the structure and evolutionary relationship of the XTH family genes in sugar beet, and reveal the potential function of BvXTH17 in plant growth and hormone response.

Trehalose alleviates the inhibition of adventitious root formation caused by drought stress in cucumber through regulating ROS metabolism and activating trehalose and plant hormone biosynthesis

Trehalose (Tre) plays a vital role in response to drought stress in plants but its regulatory mechanism remains unclear. Here, this study explores the mechanism of re-regulated drought tolerance during cucumber adventitious root formation. Our results indicate that 2 mM Tre displays remarkable drought alleviation in the aspect of root number, root length, fresh weight, and dry weight. Under drought stress, Tre could inhibit greatly the MDA, H2O2, and O2- accumulation, enhance obviously the activities of SOD, POD, and CAT enzymes and up-regulate significantly the transcript levels of SOD, POD, and CAT genes. Furthermore, Tre treatment also promotes Tre metabolism during drought stress: significantly increases starch and Tre contents and decreases glucose content, the biosynthesis enzymatic activity of the Tre metabolic pathway including TPS and TPP are enhanced and the activity of degradation enzyme THL is decreased, and corresponding genes TPS1, TPS2, TPPA, and TPPB are up-regulated. Tre significantly reversed the decrease caused by PEG in IAA, ethylene, ABA, and BR contents and the increase caused by PEG in GA3 and KT contents. Collectively, Tre appears to be the effective treatment in counteracting the negative effects of drought stress during adventitious root formation by regulating ROS, Tre metabolisms and plant hormones.

24-Epibrassinolide Facilitates Adventitious Root Formation by Coordinating Cell-Wall Polyamine Oxidase- and Plasma Membrane Respiratory Burst Oxidase Homologue-Derived Reactive Oxygen Species in Capsicum annuum L

Adventitious root (AR) formation is a critical process in cutting propagation of horticultural plants. Brassinosteroids (BRs) have been shown to regulate AR formation in several plant species; however, little is known about their exact effects on pepper AR formation, and the downstream signaling of BRs also remains elusive. In this study, we showed that treatment of 24-Epibrassinolide (EBL, an active BR) at the concentrations of 20-100 nM promoted AR formation in pepper (Capsicum annuum). Furthermore, we investigated the roles of apoplastic reactive oxygen species (ROS), including hydrogen peroxide (H₂O₂) and superoxide radical (O₂^•-), in EBL-promoted AR formation, by using physiological, histochemical, bioinformatic, and biochemical approaches. EBL promoted AR formation by modulating cell-wall-located polyamine oxidase (PAO)-dependent H₂O₂ production and respiratory burst oxidase homologue (RBOH)-dependent O₂^•- production, respectively. Screening of CaPAO and CaRBOH gene families combined with gene expression analysis suggested that EBL-promoted AR formation correlated with the upregulation of CaPAO1, CaRBOH2, CaRBOH5, and CaRBOH6 in the AR zone. Transient expression analysis confirmed that CaPAO1 was able to produce H₂O₂, and CaRBOH2, CaRBOH5, and CaRBOH6 were capable of producing O₂^•-. The silencing of CaPAO1, CaRBOH2, CaRBOH5, and CaRBOH6 in pepper decreased the ROS accumulation and abolished the EBL-induced AR formation. Overall, these results uncover one of the regulatory pathways for BR-regulated AR formation, and extend our knowledge of the functions of BRs and of the BRs-ROS crosstalk in plant development.

Metabolomics reveals the response of hydroprimed maize to mitigate the impact of soil salinization

Soil salinization is a major environmental stressor hindering global crop production. Hydropriming has emerged as a promising approach to reduce salt stress and enhance crop yields on salinized land. However, a better mechanisitic understanding is required to improve salt stress tolerance. We used a biochemical and metabolomics approach to study the effect of salt stress of hydroprimed maize to identify the types and variation of differentially accumulated metabolites. Here we show that hydropriming significantly increased catalase (CAT) activity, soluble sugar and proline content, decreased superoxide dismutase (SOD) activity and peroxide (H₂O₂) content. Conversely, hydropriming had no significant effect on POD activity, soluble protein and MDA content under salt stress. The Metabolite analysis indicated that salt stress significantly increased the content of 1278 metabolites and decreased the content of 1044 metabolites. Ethisterone (progesterone) was the most important metabolite produced in the roots of unprimed samples in response to salt s tress. Pathway enrichment analysis indicated that flavone and flavonol biosynthesis, which relate to scavenging reactive oxygen species (ROS), was the most significant metabolic pathway related to salt stress. Hydropriming significantly increased the content of 873 metabolites and significantly decreased the content of 1313 metabolites. 5-Methyltetrahydrofolate, a methyl donor for methionine, was the most important metabolite produced in the roots of hydroprimed samples in response to salt stress. Plant growth regulator, such as melatonin, gibberellin A8, estrone, abscisic acid and brassinolide involved in both treatment. Our results not only verify the roles of key metabolites in resisting salt stress, but also further evidence that flavone and flavonol biosynthesis and plant growth regulator relate to salt tolerance.

A methane-cGMP module positively influences adventitious rooting

KEY MESSAGE

Endogenous cGMP operates downstream of CH₄ control of adventitious rooting, following by the regulation in the expression of cell cycle regulatory and auxin signaling-related genes. Methane (CH₄) is a natural product from plants and microorganisms. Although exogenously applied CH₄ and cyclic guanosine monophosphate (cGMP) are separately confirmed to be involved in the control of adventitious root (AR) formation, the possible interaction still remains elusive. Here, we observed that exogenous CH₄ not only rapidly promoted cGMP synthesis through increasing the activity of guanosine cyclase (GC), but also induced cucumber AR development. These responses were obviously impaired by the removal of endogenous cGMP with two GC inhibitors. Anatomical evidence showed that the emerged stage (V) among AR primordia development might be the main target of CH₄-cGMP module. Genetic evidence revealed that the transgenic Arabidopsis that overexpressed the methyl-coenzyme M reductase gene (MtMCR) from Methanobacterium thermoautotrophicum not only increased-cGMP production, but also resulted in a pronounced AR development compared to wild-type (WT), especially with the addition of CH₄ or the cell-permeable cGMP derivative 8-Br-cGMP. qPCR analysis confirmed that some marker genes associated with cell cycle regulatory and auxin signaling were closely related to the brand-new CH₄-cGMP module in AR development. Overall, our results clearly revealed an important function of cGMP in CH₄ governing AR formation by modulating auxin-dependent pathway and cell cycle regulation.