Drought is a global threat that affects agricultural production. Plants have evolved several adaptive strategies to cope with drought. Stomata are essential structures for plants to control water status and photosynthesis rate. Stomatal closure is an efficient way for plants to reduce water loss and improve survivability under drought conditions. The opening and closure of stomata depend on the turgor pressure in guard cells. Three key signaling molecules, including abscisic acid (ABA), reactive oxygen species (ROS), and calcium ion (Ca2+), play pivotal roles in controlling stomatal closure. Plants sense the water-deficit signal mainly via leaves and roots. On the one hand, ABA is actively synthesized in root and leaf vascular tissues and transported to guard cells. On the other hand, the roots sense the water-deficit signal and synthesize CLAVATA3/EMBRYO-SURROUNDING REGION RELATED 25 (CLE25) peptide, which is transported to the guard cells to promote ABA synthesis. ABA is perceived by pyrabactin resistance (PYR)/PYR1-like (PYL)/regulatory components of ABA receptor (RCAR) receptors, which inactivate PP2C, resulting in activating the protein kinases SnRK2s. Many proteins regulating stomatal closure are activated by SnRK2s via protein phosphorylation. ABA-activated SnRK2s promote apoplastic ROS production outside of guard cells and transportation into the guard cells. The apoplastic H2O2 can be directly sensed by a receptor kinase, HYDROGEN PEROXIDE-INDUCED CA2+ INCREASES1 (HPCA1), which induces activation of Ca2+ channels in the cytomembrane of guard cells, and triggers an increase in Ca2+ in the cytoplasm of guard cells, resulting in stomatal closure. In this review, we focused on discussing the signaling transduction of ABA, ROS, and Ca2+ in controlling stomatal closure in response to drought. Many critical genes are identified to have a function in stomatal closure under drought conditions. The identified genes in the process can serve as candidate genes for genetic engineering to improve drought resistance in crops. The review summarizes the recent advances and provides new insights into the signaling regulation of stomatal closure in response to water-deficit stress and new clues on the improvement of drought resistance in crops.

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Drought is a major environmental threat that limits crop growth, development, and productivity worldwide. Improving drought resistance with genetic engineering methods is necessary to tackle global climate change. It is well known that NAC (NAM, ATAF and CUC) transcription factors play a critical role in coping with drought stress in plants. In this study, we identified an NAC transcription factor ZmNAC20, which regulates drought stress response in maize. ZmNAC20 expression was rapidly upregulated by drought and abscisic acid (ABA). Under drought conditions, the ZmNAC20-overexpressing plants had higher relative water content and survival rate than the wild-type maize inbred B104, suggesting that overexpression of ZmNAC20 improved drought resistance in maize. The detached leaves of ZmNAC20-overexpressing plants lost less water than those of wild-type B104 after dehydration. Overexpression of ZmNAC20 promoted stomatal closure in response to ABA. ZmNAC20 was localized in the nucleus and regulated the expression of many genes involved in drought stress response using RNA-Seq analysis. The study indicated that ZmNAC20 improved drought resistance by promoting stomatal closure and activating the expression of stress-responsible genes in maize. Our findings provide a valuable gene and new clues on improving crop drought resistance.

The IP Multimedia Subsystem (IMS) is an access-independent, IP based service control architecture. Although, the security and data privacy aspects are very important in the IMS global objectives, they attract little attention so far. Secure access to multimedia services is based on SIP and HTTP digest on top of IMS architecture. Authentication is only based on SIP and is directly coupled to the SIP registration procedure. The third Generation Partnership Project (3GPP) provided Generic Bootstrapping Architecture (GBA) to authenticate the subscriber before accessing multimedia services over HTTP however through a heavy process. In this paper, we propose a new IMS Service Authentication scheme using Identity Based cryptography (IBC). Our solution enhances the security of the IMS authentication process and is promising in enabling new social services since it is based on the user's identity (which could be mapped to his presence). We analyzed the security of our new protocol and we began the evaluation of its performance. We obtained a better security as well as a performance gain compared to the classical service authentication approach in IMS.

Abstract. The advances in IPTV technology enable a new user-centric and interactive TV model, in which context-awareness concept is promising in making users' interaction with the TV dynamic and transparent. In this paper we present several existing contributions that employ context-awareness concept to allow interactive services. Some of these contributions directly focus on TV, while others are proposed for specific NGN services. We analyze these contributions based upon some requirements that we define for enabling advanced IPTV services personalization.