Differentially Expressed Genes During Early Infection Of Phytophthora Sojae With Soybean Plant And Functional Analysis Of Some Genes

Phytophthora sojae is an aggressive pathogen that is able to infect and kill soybean plants throughout much of the growing season and leads to annual soybean production losses around the world with the worth of over one billion. P. sojae is one of the pathogenic oomycetes which are classified in the kingdom Protoctista and are related to heterokont , biflagellate, golden-brown algae while fungi form a separate kingdom and are evolutionarily related to animals. So it is easy to understand that many pathogenicity mechanisms of plant fungal pathogens are not suitable to the oomycete pathogens. Unfortunately, too little is known about the molecular mechanisms of the pathogenicity of oomycetes. Thus, studies on the pathogenicity mechanisms of oomycetes including P. sojae will help us to find special molecular targets of controlling the oomycete diseases. In order to learn more about genes which are induced or inhibited in the host and pathogen during a susceptible interaction, we constructed two cDNA libraries by SSH method. In addition, we selected two genes PsPHGPx and PsDIP which could function as antioxidation and effector during nonhost resistance to elucidate their functions.Firstly, to investigate patterns of gene expression in the pathogen during an infection time course, we employed subtractive suppression hybridization (SSH) between RNA isolated from P. sojae mycelium grown in 20% tomato juice with CaCO₃ and on the leaf surface of Glycine max cultivar Hefeng 35. Following SSH, expression of clones was examined using dot-blot macro-arrays and virtual Northern blots. One hundred and five unigenes were found from 487 positive clones screened from SSH libraries, in which 43 and 62 unigenes belonged to up-regulated and down-regulated genes libraries respectively. These genes involved in energy, transcription, signal transduction and redox which indicated that the infection process of P. sojae was complex and mangy genes could participate in the process. Intriguingly, the gene of creatine kinase which was found only in animal was up-regualted while cytochrome C which functioned as an electron carrier in the respiration chain was down-regulated corresponding to creatine kinase, which...