## 5 Phytoalexin Accumulation in the Upregulation of Defense-Related Marker and Elicitor Genes
Two compounds, sakurantein and momilactone A, respectively, flavanone and diterpenoid phytoalexins from rice had their concentrations increased by 4-fold and 32-fold following infection by the rice blast fungal pathogen _Magnaporthe grisea_, in _OsACDR1_ overexpressing lines while their accumulation in vector control plants were nil or negligible. The fact that _OsACDR1_ overexpressing plants exhibited enhanced disease resistance to _M. grisea_ through a reduction in the ability of fungal appressoria to penetrate into plant cells could be indirectly related with phytoalexin accumulation in transgenic lines. Conversely, _Osacdr1_ knock-out and OsACDR1-RNAi rice plants showed increased susceptibilities to the pathogen though no information regarding a possible relationship between the loss-of-function of _OsACDR1_, decreased-disease resistance and phytoalexin content were provided in this study. Systemic Acquired Resistance (SAR) is a long lasting defense response that is induced by localized infection providing subsequent protection against a broad spectrum of pathogens [142]. Resistance to several fungal and bacterial diseases has been obtained by overexpression the Non-expressor of Pathogenesis-Related genes-1 (_NPR1_) in many plant species. NPRs1 play a critical role in SAR [143] and validation of their involvement in various defense networks arose from a number of overexpression studies. For instance, overexpression of _NPR1_ was shown to confer resistance to bacteria, viruses and fungi in rice, [144], tomato [145], wheat [146] and carrot [147]. Recently, resistance against various fungal pathogens and a reinfor nematode was obtained in transgenic cotton overexpressing _Arabidopsis NPR1_ (_AtNPR1_) [148]. The _AtNPR1_-expressing lines which displayed namely high level of resistance to _Verticillium dahliae_ had corresponding high levels of gossypol, a phytoalexin from cotton and derivated terpenoids, forming part of the overall defense response that protects the _AtNPR1_-transformants from disease. The Rac family also named Rop family belongs to the Ras superfamily of GTPases. This family constitutes one of the most important regulators of signal transduction in plants, participating to their adaptation to various environmental situations [149]. Rac proteins are also involved in innate immunity namely in rice and barley [149, 150, 151]. Importantly, the _Oryza sativa_ Rac family OsRac1 forms a complex termed defensome with downstream proteins which regulate reactive oxygen intermediate (ROI) production, hypersensitive-like responses, lignin biosynthesis and phytoalexin accumulation as well as the transcription of pathogenesis-related genes [150, 152]. Transgenic rice plants expressing the constitutively active OsRac1 exhibited HR-like responses and increased resistance both to a virulent race of the rice blast fungus and a virulent race of bacterial blight together with an enhancement of the production of the rice phytoplankton momilactone A (19- to 180-fold higher than the levels of untransformed rice plants) [150]. Phytoalexin content in the transgenic lines expressing the dominant-negative OsRac1 was similar to control plants. Overexpression of an homologue of mamalian selenium-binding proteins, the rice _O. sativa_ selenium-binding protein homologue (_OsSBP_) led to increased resistance to both rice blast fungus and rice bacterial blight _via_ activation of plant defense mechanisms including accumulation of the rice phytoalexin, momilactone A [153]. Although there are some reports of the occurence of selenium binding proteins in plants, their functions remain unclear [154, 155]. A full length _OsSBP_ cDNA fragment was inserted in sense- or antisense-orientation under the control of the CaMV 35S promoter. _OsSBP_ overexpressing rice lines exhibited delayed disease symptoms upon rice blast fungus while downregulated expression of _OsSBP_ resulted in symptoms slightly more severe than in controls.