Changes in transcript levels of cassava superoxide dismutase and catalase during interaction with Phytopythium sp.

Among the biotic factors affecting the production of cassava (Manihot esculenta Crantz), root rot is one of the most severe diseases worldwide. In northern Brazil, the oomycete Phytopythium sp. causes cassava soft root rot disease in the Amazon region. Seeking to understand this plant-pathogen interaction, our main aim was to evaluate changes in expression levels of superoxide dismutase (SOD) and catalase (CAT) genes in susceptible cassava infected by Phytopythium sp., using semi-quantitative RT-PCR assays. Thus, four SOD (three CuZnSOD and one MnSOD) and three CAT genes were selected from the cassava genome available in the Phytozome Database. Comparative sequence analysis revealed high identity between the deduced MeSOD and MeCAT proteins with SODs and CATs from GenBank Database. In addition, putative conserved motifs and metal-binding domains were found within MeCuZnSOD1-3 and MeMnSOD sequences. The deduced MeCAT proteins contain putative domains and conserved motifs, such as a peroxisomal targeting signal. Furthermore, phylogenetic analysis showed that MeCuZnSOD1 and MeCuZnSOD3 proteins were related to SOD [Cu-Zn] 2 (XP_021686055.1) from Hevea brasiliensis, while MeCuZnSOD2 was close to SOD [Cu-Zn] (XP_012089157.1) from Jatropha curcas. MeMnSOD showed a phylogenetic relationship with mitochondrial SOD [Mn] (XP_021684793.1) from H. brasiliensis. The results also revealed phylogenetic proximity of MeCAT2 and MeCAT3 with CAT isozyme 2 (XP_021675148.1), while MeCAT1 was close to CAT isozyme 1 (XP_021675149.1), both from H. brasiliensis. Semi-quantitative RT-PCR assays showed that Phytopythium sp. was able to suppress the expression of MeSOD genes at early stages of infection, while at 48 h after inoculation (HAI) cassava responded by increasing the expression of the MeCuZnSOD3 gene. For the CAT genes, the MeCAT1 gene showed an expression pattern similar to MeCuZnSOD3, while the expression of the MeCAT3 gene was increased at 24 and 48 HAI. The results revealed that cassava responded to Phytopythium sp. infection through changes in transcript levels of different SOD and CAT isoforms, which are known enzymes with crucial functions regarding the oxidative burst produced during plant-pathogen interactions.