Melatonin is known to involve multiple physiological actions in plants. Herein, we found that exogenous melatonin inhibited the Arabidopsis seedling growth through the elevated abscisic acid (ABA) levels, and the elevated ABA was ascribed to the upregulation of 9‐cis‐epoxycarotenoid dioxygenase genes (NCEDs) in the ABA biosynthesis pathway. We also found that the overexpression lines of the melatonin receptor gene PMTR1 (also known as Cand2) yielded smaller seeds and germinated slower than the wild type, whereas PMTR1‐knockout mutants produced larger seeds and germinated faster than the wild type. During the seed development, the accumulation peak of ABA was higher in the PMTR1‐knockout mutant, while it was lower in the PMTR1‐overexpression line than that in the wild type. In the dry seeds and imbibed seeds, the PMTR1‐overexpression line accumulated higher ABA levels, while the PMTR1‐knockout contained less ABA than the wild type. In summary, our findings suggest that PMTR1 is involved in ABA‐mediated seed development and germination in Arabidopsis.

An efficient and selective pretreatment method of one-step hydrophilic interaction chromatography-based solid phase extraction (HILIC SPE) was developed using silica as the sorbent to quickly and sensitively detect endogenous ABA and its five catabolites in fresh Oryza sativa tissues. The extracted analytes were sensitively quantified with ultra high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS). Under the optimized conditions, good linearity of the developed analytical method was obtained in the range of 0.2–1000 ng/mL with linear correlation coefficients (r) greater than 0.9987. The limits of detection (LODs, signal/noise = 3) ranged from 0.01 to 0.74 ng/mL. The relative recoveries were between 83.3% and 112.0% with the relative standard deviations (RSDs) ranging from 0.5 to 15.0%. Using the proposed method, the concentration variations of ABA and its catabolites were monitored in the salt-stressed rice tissues.

Bile acids (BAs) are a type of gut microbiota–host cometabolites with abundant structural diversity, and they play critical roles in maintaining host–microbiota homeostasis. In this study, we developed a new N-(4-aminomethylphenyl) pyridinium (AMPP) derivatization-assisted alternating dual-collision energy scanning mass spectrometry (AMPP-dual-CE MS) method for the profiling of BAs derived from host–gut microbiota cometabolism in mice. Using the proposed method, we discovered two new types of amino acid conjugations (alanine conjugation and proline conjugation) and acetyl conjugation with host BAs, for the first time, from mouse intestine contents and feces. Additionally, we also determined and identified nine new leucine- and phenylalanine-conjugated BAs. These findings broaden our knowledge of the composition of the BA pool and provide insight into the mechanism of host–gut microbiota cometabolism of BAs.

Phaseic acid (PA), a main catabolite of abscisic acid (ABA), is structurally related to ABA and possesses ABA-like hormonal activity. However, the comprehensive metabolism pathway and roles of PA is not well understood. Here, we identified the previously named CRL1 (Cinnamoyl coA:NADP oxidoreductase like 1) as a PA reductase that catalyzes PA to dihydrophaseic acid (DPA) via a homologous alignment and expression pattern analysis strategy in Arabidopsis. The function of CRL1 and the potential role of PA were studied in the genetically transgenic material of CRL1. Overexpression of CRL1 (OE) resulted in decreased ABA sensitivity in seed germination and attenuated drought tolerance. In contrast, increased ABA sensitivity and elevated drought tolerance was observed in down-regulated and loss-of-function crl1 mutants. The Tyr162 residues in the conserved motif of CRL1 is key to the PA catalytic activity. Accelerated seed germination and earlier flowering phenotype was also observed in OE lines, while retarded seed germination and delayed flowering time in crl1 mutants which accumulated more PA while less DPA than the wildtype (WT). This study demonstrates that PA plays diverse functions in plant including drought tolerance, seed germination and flowering in an ABA-like manner, which may expand the plant adaptive plasticity.

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cis-Diol-containing metabolites are widely distributed in living organisms, and they participate in the regulation of various important biological activities. The profiling of cis-diolcontaining metabolites could help us in fully understanding their functions. In this work, based on the characteristic isotope pattern of boron, we employed a boronic acid reagent as the isotope tag to establish a sensitive and selective liquid chromatography−highresolution mass spectrometry method for the screening and annotation of cis-diol-containing metabolites in biological samples. Boronic acid reagent 2-methyl-4-phenylaminomethylphenylboronic acid was used to label the cis-diol-containing metabolites in biological samples to improve the selectivity and MS sensitivity of cis-diol-containing metabolites. Based on the characteristic 0.996 Da mass difference of precursor ions and the peak intensity ratio of 1:4 originating from 10 B and 11 B natural isotopes, the potential cis-diol-containing metabolites were rapidly screened from biological samples. Potential cis-diol-containing metabolites were annotated by database searching and analysis of fragmentation patterns obtained by multistage MS (MS n ) via collision-induced dissociation. Importantly, the cis-diol position could be readily resolved by the MS 3 spectrum. With this method, a total of 45 cisdiol-containing metabolites were discovered in rice, including monoglycerides, polyhydroxy fatty acids, fatty alcohols, and so forth. Furthermore, the established method showed superiority in avoiding false-positive results in profiling cis-diol-containing metabolites.