The Elongator complex-associated protein DRL1 plays a positive role in immune responses against necrotrophic fungal pathogens in Arabidopsis

Authors: WANG, CHENGGANG - University Of Florida; ZHANG, XUDONG - University Of Florida; LI, JIAN-LIANG - Sanford And Burnham Medical Research Institute; ZHANG, YANPING - University Of Florida; MOU, ZHONGLIN - University Of Florida

Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2016
Publication Date: 11/21/2016
Citation: Wang, C., Zhang, X., Li, J., Zhang, Y., Mou, Z. 2016. The Elongator complex-associated protein DRL1 plays a positive role in immune responses against necrotrophic fungal pathogens in Arabidopsis. Molecular Plant Pathology. 19(2):286-299. https://doi.org/10.1111/mpp.12516.
DOI: https://doi.org/10.1111/mpp.12516

Interpretive Summary: Fungal pathogens are a constant threat to crop plants, with necrotrophic fungi being particularly serious. These types of fungi infect and kill plant cells before feeding off the dead tissues. Plants have an immune system that allows them to recognize these and other pathogens. Infected cells produce internal signal molecules which then activate protective responses in invaded tissue. However, we don’t yet understand all the genes involved in this immune response, or how various proteins derived from these genes work to mount a defensive response. Therefore, we studied the role of a particular gene, named DRL1, which was previously suggested to play a role in plant immune responses. We used a mutated, non-functional version of DRL1 in the model plant Arabidopsis to assess what happens when these plants are inoculated with necrotrophic fungi. We found that this gene was needed by the plant to properly activate several, but not all, of its defense responses. This knowledge provides clues to potential gene targets in crop plants that could be manipulated to improve resistance to this debilitating group of fungal pathogens.

Technical Abstract: DEFORMED ROOT AND LEAVES1 (DRL1) is an Arabidopsis homologue of the yeast TOXIN TARGET4 (TOT4)/KILLER TOXIN-INSENSITIVE12 (KTI12) protein that is physically associated with the RNA polymerase II-interacting protein complex named Elongator. Mutations in DRL1 and Elongator lead to similar morphological and molecular phenotypes, suggesting that DRL1 and Elongator may functionally overlap in Arabidopsis. We have shown previously that Elongator plays an important role in both salicylic acid (SA)- and jasmonic acid (JA)/ethylene (ET)-mediated defence responses. Here, we tested whether DRL1 also plays a similar role as Elongator in plant immune responses. Our results show that, although DRL1 partially contributes to SA-induced cytotoxicity, it does not play a significant role in SA-mediated expression of PATHOGENESIS-RELATED genes and resistance to the virulent bacterial pathogen Pseudomonas syringae pv. maculicola ES4326. In contrast, DRL1 is required for JA/ET- and necrotrophic fungal pathogen Botrytis cinerea-induced defence gene expression and for resistance to B. cinerea and Alternaria brassicicola. Furthermore, unlike the TOT4/KTI12 gene which, when overexpressed in yeast, confers zymocin resistance, a phenotype of the tot4/kti12 mutant, overexpression of DRL1 does not change B. cinerea-induced defence gene expression and resistance to this pathogen. Finally, DRL1 contains an N-terminal P-loop and a C-terminal calmodulin (CaM)-binding domain and is a CaM-binding protein. We demonstrate that both the P-loop and the CaM-binding domain are essential for the function of DRL1 in B. cinerea-induced expression of PDF1.2 and ORA59, and in resistance to B. cinerea, suggesting that the function of DRL1 in plant immunity may be regulated by ATP/GTP and CaM binding.