(E.H.).MAX2 (for MORE AXILLARY GROWTH2) has been shown to regulate diverse biological processes, including plant architecture, photomorphogenesis, senescence, and karrikin signaling. Although karrikin is a smoke-derived abiotic signal, a role for MAX2 in abiotic stress response pathways is least investigated. Here, we show that the max2 mutant is strongly hypersensitive to drought stress compared with wild-type Arabidopsis (Arabidopsis thaliana). Stomatal closure of max2 was less sensitive to abscisic acid (ABA) than that of the wild type. Cuticle thickness of max2 was significantly thinner than that of the wild type. Both of these phenotypes of max2 mutant plants correlate with the increased water loss and drought-sensitive phenotype. Quantitative real-time reverse transcriptionpolymerase chain reaction analyses showed that the expression of stress-responsive genes and ABA biosynthesis, catabolism, transport, and signaling genes was impaired in max2 compared with wild-type seedlings in response to drought stress. Double mutant analysis of max2 with the ABA-insensitive mutants abi3 and abi5 indicated that MAX2 may function upstream of these genes. The expression of ABA-regulated genes was enhanced in imbibed max2 seeds. In addition, max2 mutant seedlings were hypersensitive to ABA and osmotic stress, including NaCl, mannitol, and glucose. Interestingly, ABA, osmotic stress, and drought-sensitive phenotypes were restricted to max2, and the strigolactone biosynthetic pathway mutants max1, max3, and max4 did not display any defects in these responses. Taken together, these results uncover an important role for MAX2 in plant responses to abiotic stress conditions.

Gas exchange, chlorophyll (Chl) fluorescence, and contents of photosynthetic pigments, soluble proteins (ribulose-1,5bisphosphate carboxylase/oxygenase, RuBPCO), and antioxidant enzymes were characterized in the fully expanded 6 th leaves in rice seedlings grown on either complete (CK) or on nitrogen-deficient nutrient (N-deficiency) solutions during a 20-chase period. Compared with the control plants, the lower photosynthetic capacity at saturation irradiance (P max ) was accompanied by an increase in intercellular CO 2 concentration (C i ), indicating that in N-deficient plants the decline in P max was not due to stomatal limitation but due to the reduced carboxylation efficiency. The fluorescence parameters Φ PS2 , F v ′/F m ′, electron transport rate (ETR), and q P showed the same tendency as P max in N-deficient plants. Correspondingly, a higher q N paralleled the rise of the ratio of carotenoid (Car) to Chl contents. However, F v /F m was still diminished, suggesting that photoinhibition did occur in the photosystem 2 (PS2) reaction centres. In addition, the activities of antioxidant enzymes on a fresh mass basis were gradually lowered, leading to the aggravation of membrane lipid peroxidation with the proceeding N-deficiency. The accumulation of malonyldialdehyde resulted in the lessening of Chl and soluble protein content. Analyses of regression showed PS2 excitation pressure (1 -q P ) was linearly correlated with the content of Chl and inversely with soluble protein (particularly RuBPCO) content. There was a lag phase in the increase of PS2 excitation pressure compared to the decrease of RuBPCO content. Therefore, the increased excitation pressure under N-deficiency is probably the result of saturation of the electron transport chain due to the limitation of the use of reductants by the Calvin cycle. Rice plants responded to N-deficiency and high irradiance by decreasing light-harvesting capacity and by increasing thermal dissipation of absorbed energy.

One of the two branches of the a-linolenic acid metabolism pathway is catalyzed by 12-oxo-phytodienoic acid reductase I, and the other is involved in jasmonic acid (JA) synthesis. The former is known to be active in the response to salinity tolerance in wheat (Triticum aestivum), but the participation of the latter in this response has not been established as yet. Here, the salinity-responsive bread wheat gene TaAOC1, which encodes an allene oxide cyclase involved in the a-linolenic acid metabolism pathway, was constitutively expressed in both bread wheat and Arabidopsis (Arabidopsis thaliana). In both species, transgenic lines exhibited an enhanced level of tolerance to salinity. The transgenic plants accumulated a higher content of JA and developed shorter roots. Both the shortened roots and the salinity tolerance were abolished in a background lacking a functional AtMYC2, a key component of the JA and abscisic acid signaling pathway, but were still expressed in a background deficient with respect to abscisic acid synthesis. We provide the first evidence, to our knowledge, suggesting that JA is also involved in the plant salinity response and that the a-linolenic acid metabolism pathway has a regulatory role over this response.

Phthalates are extensively used as plasticizers in a variety of daily-life products, resulting in widespread distribution in aquatic environments. However, limited information is available on the endocrine disrupting effects of phthalates in aquatic organisms. The aim of the present study was to examine whether exposure to mono-(2-ethylhexyl) phthalate (MEHP), the hydrolytic metabolite of di-(2-ethylhexyl) phthalate (DEHP) disrupts thyroid endocrine system in fish. In this study, zebrafish (Danio rerio) embryos were exposed to different concentrations of MEHP (1.6, 8, 40, and 200 μg/L) from 2 h post-fertilization (hpf) to 168 hpf. The whole-body content of thyroid hormone and transcription of genes involved in the hypothalamic-pituitary-thyroid (HPT) axis were examined. Treatment with MEHP significantly decreased whole-body T4 contents and increased whole-body T3 contents, indicating thyroid endocrine disruption. The upregulation of genes related to thyroid hormone metabolism (Dio2 and UGT1ab) might be responsible for decreased T4 contents. Elevated gene transcription of Dio1 was also observed in this study, which might assist to degrade increased T3 contents. Exposure to MEHP also significantly induced transcription of genes involved in thyroid development (Nkx2.1 and Pax8) and thyroid hormone synthesis (TSHβ, NIS and TG). However, the genes encoding proteins involved in TH transport (transthyretin, TTR) was transcriptionally significantly down-regulated after exposure to MEHP. Overall, these results demonstrate that acute exposure to MEHP alters whole-body contents of thyroid hormones in zebrafish embryos/larvae and changes the transcription of genes involved in the HPT axis, thus exerting thyroid endocrine toxicity.

Reactive oxygen species and auxin play important roles in the networks that regulate plant development and morphogenetic changes. However, the molecular mechanisms underlying the interactions between them are poorly understood. This study isolated a mas (More Axillary Shoots) mutant, which was identified as an allele of the mitochondrial AAA-protease AtFtSH4, and characterized the function of the FtSH4 gene in regulating plant development by mediating the peroxidase-dependent interplay between hydrogen peroxide (H2O2) and auxin homeostasis. The phenotypes of dwarfism and increased axillary branches observed in the mas (renamed as ftsh4-4) mutant result from a decrease in the IAA concentration. The expression levels of several auxin signaling genes, including IAA1, IAA2, and IAA3, as well as several auxin binding and transport genes, decreased significantly in ftsh4-4 plants. However, the H2O2 and peroxidases levels, which also have IAA oxidase activity, were significantly elevated in ftsh4-4 plants. The ftsh4-4 phenotypes could be reversed by expressing the iaaM gene or by knocking down the peroxidase genes PRX34 and PRX33. Both approaches can increase auxin levels in the ftsh4-4 mutant. Taken together, these results provided direct molecular and genetic evidence for the interaction between mitochondrial ATP-dependent protease, H2O2, and auxin homeostasis to regulate plant growth and development.

Plant meristems are responsible for the generation of all plant tissues and organs. Here we show that the transcription factor (TF) FAR-RED ELONGATED HYPOCOTYL3 (FHY3) plays an important role in both floral meristem (FM) determinacy and shoot apical meristem maintenance in Arabidopsis, in addition to its well-known multifaceted roles in plant growth and development during the vegetative stage. Through genetic analyses, we show that WUSCHEL (WUS) and CLAVATA3 (CLV3), two central players in the establishment and maintenance of meristems, are epistatic to FHY3. Using genome-wide ChIP-seq and RNA-seq data, we identify hundreds of FHY3 target genes in flowers and find that FHY3 mainly acts as a transcriptional repressor in flower development, in contrast to its transcriptional activator role in seedlings. Binding motif-enrichment analyses indicate that FHY3 may coregulate flower development with three flowerspecific MADS-domain TFs and four basic helix-loop-helix TFs that are involved in photomorphogenesis. We further demonstrate that CLV3, SEPALLATA1 (SEP1), and SEP2 are FHY3 target genes. In shoot apical meristem, FHY3 directly represses CLV3, which consequently regulates WUS to maintain the stem cell pool. Intriguingly, CLV3 expression did not change significantly in fhy3 and phytochrome B mutants before and after light treatment, indicating that FHY3 and phytochrome B are involved in light-regulated meristem activity. In FM, FHY3 directly represses CLV3, but activates SEP2, to ultimately promote FM determinacy. Taken together, our results reveal insights into the mechanisms of meristem maintenance and determinacy, and illustrate how the roles of a single TF may vary in different organs and developmental stages. meristem maintenance | meristem determinacy | FHY3 | CLV3 | SEP2 P lant meristems are responsible for the generation of all plant tissues and organs. Unlike the shoot apical meristem (SAM), whose activity is maintained throughout the life of plants, the floral meristem (FM) is precisely programmed to terminate in a process known as FM determinacy (1). WUSCHEL (WUS) plays a central role in the establishment and maintenance of SAM, inflorescence meristem, and FM, as well as in FM determinacy (2-4). WUS is expressed in the organizing center located beneath the stem cells in the meristem to promote cell proliferation by maintaining stem cell potential (2). The WUS/CLAVATA3 (CLV3) signaling pathway maintains the stabilization of meristem size and the stem cell pool (3, 5). Consistent with WUS overactivation, clv3 mutants have an enlarged SAM and increased numbers of floral organs and whorls (5). In addition to the WUS/CLV3 loop, several other pathways are known to regulate FM determinacy (4). AGAMOUS (AG) encodes a MADS-box transcription factor (TF) and is the lynchpin of the FM determinacy network (4, 6, 7). In the null ag-1 mutant, FM determinacy is severely impaired, resulting in a flower-in-flower phenotype (6). AG inhibits WUS expression through both indirect and direct means (8, 9). A number of other gene...

Summary APETALA2 (AP2) is best known for its function in the outer two floral whorls where it specifies the identities of sepals and petals by restricting the expression of AGAMOUS (AG) to the inner two whorls in Arabidopsis thaliana. Here, we describe a role of AP2 in promoting the maintenance of floral stem cell fate, not by repressing AG transcription, but by antagonizing AG activity in the center of the flower.We performed a genetic screen with ag-10 plants, which exhibit a weak floral determinacy defect, and isolated a mutant with a strong floral determinacy defect. This mutant was found to harbor another mutation in AG and was named ag-11. We performed a genetic screen in the ag-11 background to isolate mutations that suppress the floral determinacy defect. Two suppressor mutants were found to harbor mutations in AP2.While AG is known to shut down the expression of the stem cell maintenance gene WUSCHEL (WUS) to terminate floral stem cell fate, AP2 promotes the expression of WUS.AP2 does not repress the transcription of AG in the inner two whorls, but instead counteracts AG activity.

An efficient method for the simultaneous extraction and quantification of both jasmonic acid (JA) and methyl jasmonate (MeJA) from a single plant sample was developed. Plant tissues were firstly extracted by using 100% cold methanol, then the Sep-pak C 18 solid-phase extraction (SPE) cartridges were adopted for the purification of sample extract, and finally JA and MeJA were determined by the liquid chromatography tandem mass spectrometry (LC-MS-MS) system. It was found that the accuracy was improved by using the extra standard for the estimation and correction of JA and MeJA losses in the extraction and purification process. The detection limits for JA and MeJA were 0.03 and 0.075 ng mL −1 , respectively, and the average recovery rate of JA and MeJA was 92.48% and 94.30%. The method was found to be reproducible and selective, yielding well isolated and easily detectable peaks for both JA and MeJA and simplifying the time-consuming extraction and purification. High-performance liquid chromatography (HPLC) system was employed as the control detection method for the LC-MS-MS system. The two systems were compared in their specificity and accuracy. jasmonic acid, methyl jasmonate, extraction, purification, LC-MS-MS Citation: Liu X, Yang Y L, Lin W H, et al. Determination of both jasmonic acid and methyl jasmonate in plant samples by liquid chromatography tandem mass spectrometry.