Discovery of a Plant 14-3-3 Inhibitor Possessing Isoform Selectivity and In Planta Activity.

Synthetic modulators of plant 14-3-3s are promising chemical tools both for understanding the 14-3-3-related signaling pathways and controlling plant physiology. Herein, we describe a novel small-molecule inhibitor for 14-3-3 proteins of Arabidopsis thaliana. The inhibitor was identified from unexpected products in a stock solution in dimethyl sulfoxide (DMSO) of an in-house chemical library. Mass spectroscopy, mutant-based analyses, fluorescence polarization assays, and thermal shift assays revealed that the inhibitor covalently binds to an allosteric site of 14-3-3 with isoform selectivity. Moreover, infiltration of the inhibitor to Arabidopsis leaves suppressed the stomatal aperture. The inhibitor should provide new insight into the design of potent and isoform-selective 14-3-3 modulators.

Image-Based Quantification of Arabidopsis thaliana Stomatal Aperture from Leaf Images.

The quantification of stomatal pore size has long been a fundamental approach to understand the physiological response of plants in the context of environmental adaptation. Automation of such methodologies not only alleviates human labor and bias but also realizes new experimental research methods through massive analysis. Here, we present an image analysis pipeline that automatically quantifies stomatal aperture of Arabidopsis thaliana leaves from bright-field microscopy images containing mesophyll tissue as noisy backgrounds. By combining a You Only Look Once X-based stomatal detection submodule and a U-Net-based pore segmentation submodule, we achieved a mean average precision with an intersection of union (IoU) threshold of 50% value of 0.875 (stomata detection performance) and an IoU of 0.745 (pore segmentation performance) against images of leaf discs taken with a bright-field microscope. Moreover, we designed a portable imaging device that allows easy acquisition of stomatal images from detached/undetached intact leaves on-site. We demonstrated that this device in combination with fine-tuned models of the pipeline we generated here provides robust measurements that can substitute for manual measurement of stomatal responses against pathogen inoculation. Utilization of our hardware and pipeline for automated stomatal aperture measurements is expected to accelerate research on stomatal biology of model dicots.

Comparison of Survival Outcomes Between Larynx-Preserving Open Partial Pharyngectomy and Radiotherapy or Chemoradiotherapy in Patients with Hypopharyngeal Squamous Cell Carcinoma: A Single-Center Retrospective Analysis with Inverse Probability of Treatment Weighting Adjustments.

BACKGROUND: There is a group of hypopharyngeal squamous cell carcinoma (HPSCC) patients for whom larynx-preserving open partial pharyngectomy (PP) and radiotherapy/chemoradiotherapy (RT/CRT) are indicated. We aimed to retrospectively evaluate the survival difference as there is no evidence directly comparing the two therapies. METHODS: This study evaluated HPSCC patients who were initially treated by PP or RT/CRT at our institution between January 2007 and October 2019. Overall survival (OS), disease-specific survival (DSS), laryngectomy-free survival (LFS), and local relapse-free survival (LRFS) were evaluated. The main analyses were performed with inverse probability of treatment weighting (IPTW) adjustments. Sensitivity analyses compared hazard ratios (HRs) obtained with three models: unadjusted, multivariate Cox regression, and propensity score-adjusted. RESULTS: Overall, 198 patients were enrolled; 63 and 135 underwent PP and RT/CRT, respectively. IPTW-adjusted 5-year OS, DSS, LFS, and LRFS rates in the PP and RT/CRT groups were 84.3% and 61.9% (p = 0.019), 84.9% and 75.8% (p = 0.168), 94.8% and 90.0% (p = 0.010), and 75.9% and 74.1% (p = 0.789), respectively. In the IPTW-adjusted regression analysis, PP was associated with a significant benefit regarding OS (HR 0.48, 95% confidence interval [CI] 0.26-0.90) and LFS (HR 0.17, 95% CI 0.04-0.77). The results obtained with the three models in the sensitivity analyses were qualitatively similar to those of the IPTW-adjusted models. CONCLUSION: Despite the risk of bias related to unadjusted factors, our results suggest that PP is associated with significantly better OS and LFS compared with RT/CRT for HPSCC.

Green fluorescence from cnidarian hosts attracts symbiotic algae.

Reef-building corals thrive in nutrient-poor marine environments because of an obligate symbiosis with photosynthetic dinoflagellates of the genus Symbiodinium Symbiosis is established in most corals through the uptake of Symbiodinium from the environment. Corals are sessile for most of their life history, whereas free-living Symbiodinium are motile; hence, a mechanism to attract Symbiodinium would greatly increase the probability of encounter between host and symbiont. Here, we examined whether corals can attract free-living motile Symbiodinium by their green fluorescence, emitted by the excitation of endogenous GFP by purple-blue light. We found that Symbiodinium have positive and negative phototaxis toward weak green and strong purple-blue light, respectively. Under light conditions that cause corals to emit green fluorescence, (e.g., strong blue light), Symbiodinium were attracted toward live coral fragments. Symbiodinium were also attracted toward an artificial green fluorescence dye with similar excitation and emission spectra to coral-GFP. In the field, more Symbiodinium were found in traps painted with a green fluorescence dye than in controls. Our results revealed a biological signaling mechanism between the coral host and its potential symbionts.

Predicting the efficacy of chemoradiotherapy for locally advanced human papilloma virus-related oropharyngeal squamous cell carcinoma using one course of TPF chemotherapy.

PURPOSE: The standard induction chemotherapy for head and neck cancer is TPF [cisplatin (CDDP), docetaxel (DOC), and 5-fluorouracil (5-FU)]. We assessed whether one course of TPF could predict the efficacy of chemoradiotherapy for human papilloma virus (HPV)-related oropharyngeal squamous cell carcinoma. METHODS: We retrospectively reviewed 51 patients with stage III-IV HPV-related oropharyngeal squamous cell carcinoma who received one course of TPF with CDDP 60 mg/m2, DOC 60 mg/m2, and 5-FU 600 mg/m2. We recommended chemoradiotherapy for patients with complete or partial response (CR/PR), and surgery for those with stable or progressive disease (SD/PD). The endpoints were TPF-related adverse events and efficacy, chemoradiotherapy efficacy, and 2-year survival. RESULTS: Neutropenia was the most common grade ≥ 3 adverse event (88%). No grade 5 adverse events occurred. TPF achieved CR in 4% of patients (2/51), PR in 73% (37/51), SD in 20% (10/51), and PD in 4% (2/51). Concurrent cetuximab and radiotherapy (bio-radiotherapy, BRT) were administered to 61% of patients (31/51), concurrent CDDP and radiotherapy (CDDP-RT) to 16% (8/51), RT alone to 2% (1/51), and surgery was performed for 22% (11/51). CR was achieved in 85% of the chemoradiotherapy group, and the rate tended to increase with TPF efficacy. CR was achieved in 84% (26/31) of patients receiving BRT, 88% (7/8) receiving CDDP-RT, and 100% (1/1) receiving RT. The 2-year survival rates were 92% overall, and 97% and 79% in the chemoradiotherapy and surgery groups, respectively. CONCLUSIONS: When facing difficulty in deciding between chemoradiotherapy and surgery, one course of TPF may be an effective option.

Heat Induction of Cyclic Electron Flow around Photosystem I in the Symbiotic Dinoflagellate Symbiodinium.

Increases in seawater temperature impair photosynthesis (photoinhibition) in the symbiotic dinoflagellate Symbiodinium within cnidarian hosts, such as corals and sea anemones, and may destroy their symbiotic relationship. Although the degree of photoinhibition in Symbiodinium under heat stress differs among strains, the differences in their responses to increased temperatures, including cyclic electron flow (CEF), which sustains photoprotective thermal energy dissipation, have not been investigated. Here, we examined CEF in cultured Symbiodinium cells or those in an endosymbiotic relationship within a cnidarian host. The light-dependent reduction of the primary electron donor photosystem I, i.e. P700(+), was enhanced in any Symbiodinium cell by increasing temperatures, indicating CEF was induced by heat, which was accompanied by thermal energy dissipation activation. The critical temperatures for inducing CEF were different among Symbiodinium strains. The clade A strains with greater susceptibility to photoinhibition, OTcH-1 and Y106, exhibited higher CEF activities under moderate heat stress than a more phototolerant clade B strain Mf1.05b, suggesting that the observed CEF induction was not a preventive measure but a stress response in Symbiodinium.

Optical Resolution, Determination of Absolute Configuration, and Photoracemization of cis-RuL2(CN)2 (L = 2,2'-Bipyridine and Its Analogues).

We synthesized neutral Ru(II) complexes cis-Ru(bpy)2(CN)2 (bpy = 2,2'-bipyridine), cis-Ru(dmb)2(CN)2 (dmb = 4,4'-dimethyl-2,2'-bipyridine), cis-Ru(dbb)2(CN)2 (dbb = 4,4'-di-tert-butyl-2,2'-bipyridine), and cis-Ru(phen)2(CN)2 (phen = 1,10-phenanthroline) and optically resolved them into respective enantiomers using high-performance liquid chromatography with a chiral column. The absolute configuration of enantiomer of cis-Ru(dbb)2(CN)2 was determined by an X-ray crystallography. Upon photoirradiation, the entire enantiomers of the complexes underwent the racemization with considerably slow rates (k = 1 × 10(-6) to 1 × 10(-5) s(-1)) and small quantum yields (ϕ = 1 × 10(-6) to 1 × 10(-5)). The photoracemization was concluded to proceed via a five-coordinate pyramidal intermediate with the base plane composed of Ru, bidentate polypyridine, and two cyanides and the axial ligand of monodentate polypyridine. We derived the equations for photoracemization rate and quantum yield by a kinetics analysis of the photoracemization reaction that depended on polypyridine ligand, solvent, temperature, wavelength and intensity of irradiation light, and emission lifetime. From the temperature-dependent photoracemization reaction, the energy gap between (3)MLCT (metal-to-ligand charge transfer) and (3)d-d* states was estimated as ΔE = 4000-5000 cm(-1), and the energy of invisible (3)d-d* state was estimated to be ca. 20 500 cm(-1), which was in good agreement with that of [Ru(bpy)3](2+).

Light-induced conformational changes of LOV1 (light oxygen voltage-sensing domain 1) and LOV2 relative to the kinase domain and regulation of kinase activity in Chlamydomonas phototropin.

Phototropin (phot), a blue light (BL) receptor in plants, has two photoreceptive domains named LOV1 and LOV2 as well as a Ser/Thr kinase domain (KD) and acts as a BL-regulated protein kinase. A LOV domain harbors a flavin mononucleotide that undergoes a cyclic photoreaction upon BL excitation via a signaling state in which the inhibition of the kinase activity by LOV2 is negated. To understand the molecular mechanism underlying the BL-dependent activation of the kinase, the photochemistry, kinase activity, and molecular structure were studied with the phot of Chlamydomonas reinhardtii. Full-length and LOV2-KD samples of C. reinhardtii phot showed cyclic photoreaction characteristics with the activation of LOV- and BL-dependent kinase. Truncation of LOV1 decreased the photosensitivity of the kinase activation, which was well explained by the fact that the signaling state lasted for a shorter period of time compared with that of the phot. Small angle x-ray scattering revealed monomeric forms of the proteins in solution and detected BL-dependent conformational changes, suggesting an extension of the global molecular shapes of both samples. Constructed molecular model of full-length phot based on the small angle x-ray scattering data proved the arrangement of LOV1, LOV2, and KD for the first time that showed a tandem arrangement both in the dark and under BL irradiation. The models suggest that LOV1 alters its position relative to LOV2-KD under BL irradiation. This finding demonstrates that LOV1 may interact with LOV2 and modify the photosensitivity of the kinase activation through alteration of the duration of the signaling state in LOV2.

The phototropic response is locally regulated within the topmost light-responsive region of the Arabidopsis thaliana seedling.

Phototropism is caused by differential cell elongation between the irradiated and shaded sides of plant organs, such as the stem. It is widely accepted that an uneven auxin distribution between the two sides crucially participates in this response. Plant-specific blue-light photoreceptors, phototropins (phot1 and phot2), mediate this response. In grass coleoptiles, the sites of light perception and phototropic bending are spatially separated. However, these sites are less clearly distinguished in dicots. Furthermore, the exact placement of the action of each phototropic signaling factor remains unknown. Here, we investigated the spatial aspects of phototropism using spotlight irradiation with etiolated Arabidopsis seedlings. The results demonstrated that the topmost part of about 1.1 mm of the hypocotyl constituted the light-responsive region in which both light perception and actual bending occurred. In addition, cotyledons and the shoot apex were dispensable for the response. Hence, the response was more region autonomous in dicots than in monocots. We next examined the elongation rates, the levels of phot1 and the auxin-reporter gene expression along the hypocotyl during the phototropic response. The light-responsive region was more active than the non-responsive region with respect to all of those parameters.

Mutations in N-terminal flanking region of blue light-sensing light-oxygen and voltage 2 (LOV2) domain disrupt its repressive activity on kinase domain in the Chlamydomonas phototropin.

Phototropin is a light-regulated kinase that mediates a variety of photoresponses such as phototropism, chloroplast positioning, and stomata opening in plants to increase the photosynthetic efficiency. Blue light stimulus first induces local conformational changes in the chromophore-bearing light-oxygen and voltage 2 (LOV2) domain of phototropin, which in turn activates the serine/threonine (Ser/Thr) kinase domain in the C terminus. To examine the kinase activity of full-length phototropin conventionally, we employed the budding yeast Saccharomyces cerevisiae. In this organism, Ser/Thr kinases (Fpk1p and Fpk2p) that show high sequence similarity to the kinase domain of phototropins exist. First, we demonstrated that the phototropin from Chlamydomonas reinhardtii (CrPHOT) could complement loss of Fpk1p and Fpk2p to allow cell growth in yeast. Furthermore, this reaction was blue light-dependent, indicating that CrPHOT was indeed light-activated in yeast cells. We applied this system to a large scale screening for amino acid substitutions in CrPHOT that elevated the kinase activity in darkness. Consequently, we identified a cluster of mutations located in the N-terminal flanking region of LOV2 (R199C, L202L, D203N/G/V, L204P, T207I, and R210H). An in vitro phosphorylation assay confirmed that these mutations substantially reduced the repressive activity of LOV2 on the kinase domain in darkness. Furthermore, biochemical analyses of the representative T207I mutant demonstrated that the mutation affected neither spectral nor multimerization properties of CrPHOT. Hence, the N-terminal flanking region of LOV2, as is the case with the C-terminal flanking Jα region, appears to play a crucial role in the regulation of kinase activity in phototropin.

BCOR-CCNB3 sarcoma arising in the pharynx.

Reports on BCOR-CCNB3 sarcoma in the head and neck region are scarce, given their unknown etiology. An 18-year-old male patient presented a rapidly enlarging tumor extending from the right nasopharynx to the oropharynx. Histological examination showed a spindle cell sarcoma with BCOR-CCNB3 fusion detected by fluorescence in situ hybridization, and BCOR-CCNB3 was diagnosed. After three courses of alternating VDC-IE therapy, the patient underwent tumor resection based on the original tumor range with a minimal margin, using the mandibular swing technique. Radiation therapy (50.4 Gy) was administered postoperatively, followed by three additional courses of alternating VDC-IE therapy. The patient survived and showed no evidence of disease at 12 months postoperatively. BCOR-CCNB3 sarcoma is a chemotherapy-sensitive sarcoma, and conservative resection with a minimal margin that does not interfere with the treatment flow is preferable.

Clinical and pathological features of second primary neoplasms arising in head and neck reconstructive skin flaps.

The incidence of second primary neoplasms arising in the skin reconstructive flap (SNAF) is increasing because of the increase in head and neck flap reconstruction and cancer survival. Prognosis, optimal treatment, and their clinicopathological-genetic features are under debate and are difficult to diagnose. We retrospectively reviewed SNAFs based on a single center's experience over 20 years. Medical records and specimens of 21 patients with SNAF who underwent biopsies between April 2000 and April 2020 at our institute were retrospectively analyzed. Definite squamous cell carcinoma and the remaining neoplastic lesions were subclassified as flap cancer (FC) and precancerous lesions (PLs), respectively. Immunohistochemical studies focused on p53 and p16. TP53 sequencing was conducted using next-generation sequencing. Seven and 14 patients had definite FC and PL, respectively. The mean number of biopsies/latency intervals was 2.0 times/114 months and 2.5 times/108 months for FC and PL, respectively. All lesions were grossly exophytic and accompanied by inflamed stroma. In FC and PL, the incidences of altered p53 types were 43% and 29%, respectively, and those of positive p16 stains were 57% and 64%, respectively. Mutation of TP53 in FC and PL were 17% and 29%, respectively. All except one patient with FC under long-term immunosuppressive therapy survived in this study. SNAFs are grossly exophytic tumors with an inflammatory background and show a relatively low altered p53 and TP53 rate and a high p16 positivity rate. They are slow-growing neoplasms with good prognoses. Diagnosis is often difficult; therefore, repeated or excisional biopsy of the lesion may be desirable.

Discovery of 2,6-Dihalopurines as Stomata Opening Inhibitors: Implication of an LRX-Mediated H+-ATPase Phosphorylation Pathway.

Stomata are pores in the leaf epidermis of plants and their opening and closing regulate gas exchange and water transpiration. Stomatal movements play key roles in both plant growth and stress responses. In recent years, small molecules regulating stomatal movements have been used as a powerful tool in mechanistic studies, as well as key players for agricultural applications. Therefore, the development of new molecules regulating stomatal movement and the elucidation of their mechanisms have attracted much attention. We herein describe the discovery of 2,6-dihalopurines, AUs, as a new stomatal opening inhibitor, and their mechanistic study. Based on biological assays, AUs may involve in the pathway related with plasma membrane H+-ATPase phosphorylation. In addition, we identified leucine-rich repeat extensin proteins (LRXs), LRX3, LRX4 and LRX5 as well as RALF, as target protein candidates of AUs by affinity based pull down assay and molecular dynamics simulation. The mechanism of stomatal movement related with the LRXs-RALF is an unexplored pathway, and therefore further studies may lead to the discovery of new signaling pathways and regulatory factors in the stomatal movement.

Identification and improvement of isothiocyanate-based inhibitors on stomatal opening to act as drought tolerance-conferring agrochemicals.

Stomatal pores in the plant epidermis open and close to regulate gas exchange between leaves and the atmosphere. Upon light stimulation, the plasma membrane (PM) H+-ATPase is phosphorylated and activated via an intracellular signal transduction pathway in stomatal guard cells, providing a primary driving force for the opening movement. To uncover and manipulate this stomatal opening pathway, we screened a chemical library and identified benzyl isothiocyanate (BITC), a Brassicales-specific metabolite, as a potent stomatal-opening inhibitor that suppresses PM H+-ATPase phosphorylation. We further developed BITC derivatives with multiple isothiocyanate groups (multi-ITCs), which demonstrate inhibitory activity on stomatal opening up to 66 times stronger, as well as a longer duration of the effect and negligible toxicity. The multi-ITC treatment inhibits plant leaf wilting in both short (1.5 h) and long-term (24 h) periods. Our research elucidates the biological function of BITC and its use as an agrochemical that confers drought tolerance on plants by suppressing stomatal opening.

Photoinduced Synthesis of Thiocyanates through Hydrogen Atom Transfer and One-Pot Derivatization to Isothiocyanates.

Photoinduced benzylic C-H thiocyanation is described. A series of alkyl thiocyanates were efficiently obtained by using Selectfluor as the oxidant. Moreover, we accomplished the one-pot isothiocyanation following the C-H thiocyanation. The thiocyanates and isothiocyanates were applied to the divergent transformation of pharmaceuticals.

Minocycline-induced black thyroid with black pigmentation of the thyroid cartilage, cricoid cartilage, and trachea found during reconstructive surgery for hypopharyngeal cancer.

Black thyroid is characterized by a rare pigment change observed almost exclusively in patients taking minocycline. We present the case of a 72-year-old man diagnosed with T3N3bM0 stage IVB hypopharyngeal squamous cell carcinoma who had been taking minocycline for approximately 18 months as a treatment for prurigo chronica multiformis. Initial treatment consisted of total pharyngolaryngoesophagectomy, bilateral neck dissection, total thyroidectomy, pharyngeal reconstruction using a free jejunal autograft, and creation of a permanent tracheostoma. During surgery, black discoloration of the thyroid and trachea was observed. Postoperative histological findings confirmed the black discoloration, with deposits of dark-brown, melanin-like granules observed in the thyroid, trachea, thyroid cartilage, and cricoid cartilage. Therefore, the black discoloration of the thyroid associated with the use of minocycline can extend to the thyroid cartilage, cricoid cartilage, and trachea. This information is important for surgeons to recognize in order to prevent unnecessary resection due to misdiagnosis.

Nivolumab for recurrent/metastatic hypopharyngeal squamous cell carcinoma in a liver transplant recipient.

Nivolumab administration to patients with organ transplantation history requires careful management. Herein, we report the case of a living-donor liver-transplant recipient, a 52-year-old man, with recurrent and metastatic hypopharyngeal cancer treated with nivolumab. He was diagnosed with T2N2bM0 stage IVA hypopharyngeal squamous cell carcinoma. While using oral immunosuppressants (cyclosporine and mycophenolate mofetil), the patient underwent right neck dissection followed by radiotherapy as an initial treatment. Three months after radiotherapy, positron emission tomography scans revealed multiple bone metastases. We administered two courses of the EXTREME regimen, comprising cisplatin, 5-fluorouracil, and cetuximab, as the first-line treatment for distal metastasis, but the patient presented with progressive disease. The patient was administered nivolumab as the second-line treatment. The programmed death-ligand 1 (PD-L1) expression level in a biopsy specimen of the primary hypopharyngeal tumor and resected specimen of the cervical lymph node metastasis was 40% and 10%, respectively. PD-L1 expression was not detected in hepatocytes of the liver biopsy sample obtained before nivolumab introduction. The patient received four courses of nivolumab 240 mg. Although liver dysfunction was alleviated by adjusting the dose of the hepatoprotective agent and cyclosporine, the progressive disease status persisted after completing nivolumab courses. The patient died of hypopharyngeal cancer progression.

Identification of stomatal-regulating molecules from de novo arylamine collection through aromatic C-H amination.

Stomata-small pores generally found on the leaves of plants-control gas exchange between plant and the atmosphere. Elucidating the mechanism that underlies such control through the regulation of stomatal opening/closing is important to understand how plants regulate photosynthesis and tolerate against drought. However, up-to-date, molecular components and their function involved in stomatal regulation are not fully understood. We challenged such problem through a chemical genetic approach by isolating and characterizing synthetic molecules that influence stomatal movement. Here, we describe that a small chemical collection, prepared during the development of C-H amination reactions, lead to the discovery of a Stomata Influencing Molecule (SIM); namely, a sulfonimidated oxazole that inhibits stomatal opening. The starting molecule SIM1 was initially isolated from screening of compounds that inhibit light induced opening of dayflower stomata. A range of SIM molecules were rapidly accessed using our state-of-the-art C-H amination technologies. This enabled an efficient structure-activity relationship (SAR) study, culminating in the discovery of a sulfonamidated oxazole derivative (SIM*) having higher activity and enhanced specificity against stomatal regulation. Biological assay results have shed some light on the mode of action of SIM molecules within the cell, which may ultimately lead to drought tolerance-conferring agrochemicals through the control of stomatal movement.

Comparison of Dosage of Nivolumab in Efficacy and Safety for Recurrent Metastatic Squamous Cell Carcinoma.

BACKGROUND/AIM: There are no real-world comparative data of nivolumab doses of 3 mg/kg and 240 mg/body for recurrent/metastatic squamous cell carcinoma of the head and neck (R/M SCCHN). We investigated the efficacy and safety of nivolumab in treating recurrent/metastatic squamous cell carcinoma of the head and neck (R/M SCCHN) at different doses using real-world data. PATIENTS AND METHODS: R/M SCCHN patients who received nivolumab were divided into the 3 mg/kg and 240 mg/body groups and retrospectively examined for efficacy and safety. RESULTS: A total of 199 patients (3 mg/kg and 240 mg/body, 88 and 111 patients, respectively) were included. The 3 mg/kg vs. 240 mg/body groups had similar overall response rates (15% vs. 25, p=0.15), disease control rates (46% vs. 57%, p=0.15), overall survival (9.5 months vs. 10.9 months), and progression-free survival (3.7 months vs. 3.8 months, p=0.95). The incidence of immune-related adverse events was also similar in both groups. CONCLUSION: In R/M SCCHN patients, nivolumab showed similar efficacy and safety at doses of 3 mg/kg and 240 mg/body.

Protease Inhibitor-Dependent Inhibition of Light-Induced Stomatal Opening.

Stomata in the epidermis of plants play essential roles in the regulation of photosynthesis and transpiration. Stomata open in response to blue light (BL) by phosphorylation-dependent activation of the plasma membrane (PM) H+-ATPase in guard cells. Under water stress, the plant hormone abscisic acid (ABA) promotes stomatal closure via the ABA-signaling pathway to reduce water loss. We established a chemical screening method to identify compounds that affect stomatal movements in Commelina benghalensis. We performed chemical screening using a protease inhibitor (PI) library of 130 inhibitors to identify inhibitors of stomatal movement. We discovered 17 PIs that inhibited light-induced stomatal opening by more than 50%. Further analysis of the top three inhibitors (PI1, PI2, and PI3; inhibitors of ubiquitin-specific protease 1, membrane type-1 matrix metalloproteinase, and matrix metalloproteinase-2, respectively) revealed that these inhibitors suppressed BL-induced phosphorylation of the PM H+-ATPase but had no effect on the activity of phototropins or ABA-dependent responses. The results suggest that these PIs suppress BL-induced stomatal opening at least in part by inhibiting PM H+-ATPase activity but not the ABA-signaling pathway. The targets of PI1, PI2, and PI3 were predicted by bioinformatics analyses, which provided insight into factors involved in BL-induced stomatal opening.