The infection by root pathogenic oomycetes is initiated by the release from sporangia of motile, biflagellate and wall-less zoospores, which encyst and adhere to the host surface following a chemotactically and electrotactically swimming stage. The cysts germinate by forming the germ tubes and start to penetrate the plant cuticle directly with the aid of secreted enzymes and colonize host tissues. Previous studies have shown that these pre-infection structures are rich in molecules involved in establishment of infection and elicitation of plant defenses. The unraveling of the molecular processes regulating the life cycle of Phytophthora is therefore important to identify determinants of pathogenesis and develop appropriate control strategies. The heterothallic oomycete Phytophthora capsici Leonian can cause seed, root, crown, foliar and fruit rot on a number of important crops, such as solanaceous crops, cucurbits and bean crops. P. capsici is also recorded as a pathogen of Allium cepa, Nicotiana benthamiana and Arabidopsis thaliana. To date, the diseases caused by P. capsici have become devastating ones of global economic importance. The cost that P. capsici inflicts upon worldwide vegetable production is estimated to be $1 billion every year. Unfortunately, the control of P. capsici is a difficult task as there has been no available effective chemical or cultural strategy. In order to improve methods for controlling Phytophthora diseases, it is essential to understand the molecular mechanisms by which the pathogen suppresses or escapes the host plant defenses. Recent studies on plant pathogenic oomycetes have demonstrated that these pathogens accomplish their penetration and colonization of host plants by manipulating their hosts through a diverse arsenal of secreted proteins. According to their potential targeting sites in the host plant, these secreted effector proteins are Mepiroxol classified into two classes, apoplastic and cytoplasmic effectors. Apoplastic effectors, including elicitins, PcF/SCR-like proteins and NLPs, are located at the interface between pathogen and its host and fulfill a function on the outside of the host cell. Elicitins, one type of pathogen associated molecular patterns, can trigger plant cell death response, normally known as hypersensitive reaction that is characteristic of plant defense response. These proteins share a conserved 98-amino-acid domain with a characteristic signature of six cysteine residues that form three distinct disulfide bonds. Members of the PcF/SCR toxin family, small cysteine-rich proteins, are thought to be involved in the induction of plant cell death. Other toxins secreted by oomycetes belong to NLPs that elicit plant cell death in dicotyledonous plants. In contrast, 
cytoplasmic effectors are able to translocate inside host cells where they interfere with the host defense responses. Two important groups of translocated effectors are RXLR and CRN protein families. RXLR effectors are named after an N-terminal RXLR amino acid motif contained by the first characterized effectors of this class, where ��X’denotes a nonconserved amino acid residue. This motif assists in the translocation of the proteins into the Alprostadil host’s cytoplasm where the effectors function as virulence or avirulence factors depending on the host genotype. Host translocation may also occur with variations of the RXLR motif or even in the absence of any such motif may. A structural dissection of these proteins has revealed a signal peptide followed by an RXLR motif at the N-terminus, which are required for secretion and targeting of the proteins whereas the C-terminus executes the actual effector activity.