Response of AtNPR1-expressing cotton plants to Fusarium oxysporum f. sp. vasinfectum isolates.

In our earlier investigation, we had demonstrated that transgenic cotton plants expressing AtNPR1 showed significant tolerance to Fusarium oxysporum f. sp. vasinfectum, isolate 11 (Fov11) and several other pathogens. The current study was designed to further characterize the nature of the protection provided by AtNPR1 expression and its limitations. Green Fluorescent Protein-expressing Fov11 was generated and used to study the progression of the disease within the plant. The results show that the spread of the pathogen was slower in the AtNPR1-transformants compared to the wild type plants. Transcript analysis in the seedling root and hypocotyl showed that the transgenic lines are capable of launching a stronger defense response when infected with Fov11. We further confirmed that AtNPR1 transformants showed greater degree of tolerance to Fov11. However, little or no protection was observed against a related, but more virulent isolate, Fov43, and a highly virulent isolate, CA9.