Differential Expressed Genes in a Phaseolus vulgaris L. Cultivar Inoculated with Colletothrichum lindemuthianum in Presence of Silicon

Anthracnose (Colletotrichum. lindemuthianum) is the most important disease affecting common beans in Brazil. Several studies show that silicon can reduce disease symptoms in plants, playing important roles in cell wall synthesis, epicuticular wax production and activation of defense mechanism. Looking for genes responsive to pathogenic attack and Si we built two suppression subtractive cDNA libraries using the fungus tolerant and Si responsive cultivar IAC-Harmonia. The first library was constructed with mRNA collected from 15 days-old plants after 72h of inoculation and was subtracted from non-inoculated plants. The second library represents genes from 15 days-old plants grown in 75 ppm of K₂SiO₃ collected 72h after inoculation and subtracted from plants inoculated and grown in the absence of Si. A total of 960 reads were sequenced from each library. Clusters were submitted to in silico Northern analyses and showed sequences with high frequency or exclusive to each library. Thirty genes were selected and their expression patterns were analyzed after inoculation in presence/absence of Si. Quantitative Real time PCR with representative genes was performed for validation of the libraries, revealing strong activation of important genes like Al-Induced protein (9.4-fold), basic pathogenesis-related protein (9.1-fold), isocitrate lyase (81.2-fold), terpene synthase (29.6-fold) and UDP-glycosyltransferase (11-fold) in the first library, and germin-like protein (1.8-fold), cysteine-rich secretory protein (3.3-fold) and F-box/RNI like protein (2.7-fold) in the second one. The activation of target genes by biotic stress observed in presence of silicon indicates that it can improve not only the cell wall structure but activate pathogenic-related genes as well.