SUMMARY Abscisic acid (ABA) is a plant hormone that activates adaptive mechanisms to environmental stress conditions. Plant adaptive mechanisms are complex and highly modulated processes induced by stress‐responsive proteins; however, the precise mechanisms by which these processes function under adverse conditions remain unclear. Here, we isolated CaUBP12 (Capsicum annuum ubiquitin‐specific protease 12) from pepper (C. annuum) leaves. We show that CaUBP12 expression is significantly induced after exposure to abiotic stress treatments. We conducted loss‐of‐function and gain‐of‐function genetic studies to elucidate the biological functions of CaUBP12 in response to ABA and dehydration stress. CaUBP12‐silenced pepper plants and CaUBP12‐overexpressing Arabidopsis plants displayed dehydration‐sensitive and dehydration‐tolerant phenotypes, respectively; these phenotypes were characterized by regulation of transpirational water loss and stomatal aperture. Under dehydration stress conditions, CaUBP12‐silenced pepper plants and CaUBP12‐overexpressing Arabidopsis plants exhibited lower and higher expression levels of stress‐related genes, respectively, than the control plants. We isolated a CaUBP12 interaction protein, CaSnRK2.6, which is a homolog of Arabidopsis OST1; degradation of this protein was partially inhibited by CaUBP12. Similar to CaUBP12‐silenced pepper plants and CaUBP12‐overexpressing Arabidopsis plants, CaSnRK2.6‐silenced pepper plants and CaSnRK2.6‐overexpressing Arabidopsis displayed dehydration‐sensitive and dehydration‐tolerant phenotypes, respectively. Our findings suggest that CaUBP12 positively modulates the dehydration stress response by suppressing CaSnRK2.6 protein degradation.

Plant adaptive responses to environmental stress are coordinated by inhibition of plant growth and development. Abscisic acid (ABA) is a major phytohormone that regulates the stress response, and its sensitivity determines stress tolerance levels. In this study, we report the identification and functional role of a novel F-box protein, CaDIF1 (Capsicum annuum Drought-Induced F-box Protein 1). The expression of CaDIF1 in pepper leaves was induced by ABA, drought, H2O2, and NaCl treatments. In comparison with wild-type pepper plants, CaDIF1-silenced pepper plants exhibited a drought-sensitive phenotype, whereas CaDIF1-overexpressing (OX) plants exhibited ABA-sensitive and drought-tolerant phenotypes. Using a yeast two-hybrid assay, we identified CaDIS1 (C. annuum DIF1-Interacting SKP 1), which interacts with CaDIF1 in the cytoplasm and nucleus. Consistent with CaDIF1-silenced pepper plants, CaDIS1-silenced pepper plants displayed ABA insensitivity and reduced drought tolerance, and these were characterized by larger stomatal apertures and greater transpirational water loss. Taken together, our results indicate that CaDIF1 and its interacting partner CaDIS1 synergistically regulate the ABA-dependent defence signaling response to drought stress.

Plants modify their internal states to adapt to environmental stresses. Under environmental stress conditions, plants restrict their growth and development and activate defense responses. Abscisic acid (ABA) is a major phytohormone that plays a crucial role in the osmotic stress response. In osmotic stress adaptation, plants regulate stomatal closure, osmoprotectant production, and gene expression. Here, we isolated CaPRR2 – encoding a pseudo response regulator protein – from the leaves of pepper plants (Capsicum annuum). After exposure to ABA and environmental stresses, such as drought and salt stresses, CaPRR2 expression in pepper leaves was significantly altered. Under drought and salt stress conditions, CaPRR2-silenced pepper plants exhibited enhanced osmotic stress tolerance, characterized by an enhanced ABA-induced stomatal closing and high MDA and proline contents, compared to the control pepper plants. Taken together, our data indicate that CaPRR2 negatively regulates osmotic stress tolerance.

Plants as sessile organisms constantly respond to environmental stress during their growth and development. The regulation of transpiration via stomata plays crucial roles in plant adaptation to drought stress. Many enzyme-encoding genes are involved in regulation of transpiration via modulating stomatal opening and closure. Here, we demonstrate that Capsicum annuum Drought Induced Late embryogenesis abundant protein 1 (CaDIL1) gene is a critical regulator of transpirational water loss in pepper. The expression of CaDIL1 in pepper leaves was upregulated after exposure to abscisic acid (ABA) and drought. Phenotype analysis showed that CaDIL1-silenced pepper and CaDIL1-overexpressing (OX) Arabidopsis transgenic plants exhibited reduced and enhanced drought tolerance, respectively, accompanied by an altered water loss. Furthermore, ABA sensitivity was significantly lower in CaDIL1-silenced pepper, but higher in CaDIL1-OX plants, than that in control plants, which resulted in opposite responses to drought stress in these two plant types. Collectively, our data suggest that CaDIL1 positively regulates the ABA signaling and drought stress tolerance.

Adaptation to drought stress is essential for plant growth and development. Plants often adapt to water deficit conditions by activating the ABA signaling. Here, we report that the pepper CaDIK1 (Capsicum annuum Drought Induced Kinase 1) gene is essential for plant tolerance to drought stress. CaDIK1 contains a serine-threonine kinase domain, which plays a role for attachment of phosphate to the target protein. The expression levels of CaDIK1 are upregulated in pepper leaves by ABA, drought, NaCl and H 2 O 2 treatments suggesting its role in abiotic stress response. We used CaDIK1-silenced pepper and CaDIK1-overexpressing (OX) transgenic Arabidopsis plants to evaluate their responses to ABA and drought. CaDIK1-silenced pepper plants conferred a reduced ABA sensitivity and drought hypersensitivity, which was accompanied by high levels of transpirational water loss. CaDIK1-OX plants displayed opposite phenotypes to CaDIK1-silenced peppers. In contrast, substitution of Lys350 to Asn in the kinase domain of CaDIK1 did not lead to alteration of drought sensitivity. Collectively, these data indicate that CaDIK1 is a positive regulator of the ABA-mediated drought-stress tolerance.

A 65-year-old diabetic man was referred to our hospital with left facial numbness, headache, and malaise approximately 2 weeks' duration. Initially, his blood glucose level and HbA 1c level were measured at 592 mg/dL and 12.6%, respectively. With strict control of blood sugar, antibiotic therapy was started because of suspected bacterial sinusitis on initial brain magnetic resonance imaging (MRI). His symptoms seemed to improve, but the facial pain and headache were suddenly aggravated at 2 weeks of admission. He was consulted to our department. Endoscopic examination revealed the black eschar in the inferior turbinate (Figure 1). Rechecked MRI showed total lack of enhancement (black turbinate sign) of the inferior turbinate of left side on T1-weighted image (Figure 2). Under general anesthesia, the patient underwent endoscopic surgery with wide excision of the necrotic tissue. Histopathologic examination demonstrated angioinvasive hyphae with characteristics of mucormycosis (Figure 3). After surgery, he finished a 6-week course of amphotericin and he remained symptomfree 18 months later. Mucormycosis is an acute opportunistic, angioinvasive, and devastating fungal infection which is associated with high mortality rates. 1 There has been a significant increase in incidence over the last 2 decades. 2 Early and accurate diagnosis of invasive mucormycosis remains a challenge for physicians. However, patients with invasive mucormycosis initially present with nonspecific symptoms and signs, leading to delays in diagnosis and imaging modalities and cultures are not usually useful for diagnosis. 2-4 Mucor organisms have the propensity of angioinvasive hyphae that results in

Abscisic acid (ABA) is a major phytohormone that regulates plant growth, development, and abiotic/biotic stress responses. Under stress, ABA is synthesized in various plant organs, and it plays roles in diverse adaptive processes, including seed dormancy, growth inhibition, and leaf senescence, by modulating stomatal closure and gene expression. ABA receptor, clade A protein phosphatase 2C (PP2C), and SNF1-related protein kinase 2 (SnRK2) proteins have been identified as core components of ABA signaling, which is initiated via perception of ABA with receptor and subsequent activation or inactivation by phosphorylation/dephosphorylation. The findings of several recent studies have established that the post-translational modification of these components, including phosphorylation and ubiquitination/deubiquitination, play important roles in regulating their activity and stability. In this review, we discuss the functions of the core components of ABA signaling and the regulation of their activities via post-translational modification under normal and stress conditions.

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