Involvement of ZmMPK14 in Plant Defense Revealed by Comparative Expression Analysis

Mitogen-Activated Protein Kinases (MAPKs) function in signaling pathways as modules cascading between stimulus activated sensors and response mechanisms.ZmMAPK14, a group C final MAPK of this cascade was identified as a differentially expressed message in cDNA-AFLP studies of both susceptible and resistant genotypes, where a gradual induction was displayed in the resistant genotype while a clear repression occurred in the susceptible genotype in response to Puccinia sorghi (Ps) inoculation. RT-qPCR verification studies, however, did not reveal the same pattern of expression in that both displayed inductions at different levels. Ps inoculation induced a limited expression increase fluctuating between 1.5 and 2.5-fold in the susceptible genotype while a dramatic upregulation starting at 12 h with a 149-fold and gradually increasing to a maximum level of 477 folds at 72 h in resistant genotype was observed. To obtain further evidence about its role in plant defense, ZmMapk14 expression in response to applications of chitin, Salicylic Acid (SA) and H2O2 at six time points covering a 0-24 h interval were studied in both genotypes. All treatments induced ZmMapk14 expression in the resistant genotype significantly at different levels while the expressional changes in the susceptible were more complex and limited similar to the Ps inoculation levels in the susceptible. Overall, the results show that ZmMAPK14 display differential expression in resistant and susceptible genotypes in response to Ps inoculation and applied defense compounds, and it presumably functions in plant defense to Ps. KeywordsZmMAPK14, Plant Defense, SA, Chitin, H2O2