WRKY Transcription Factors in Nicotiana tabacum Modulate Plant Immunity against Whitefly via Interacting with MAPK Cascade Pathways

SIMPLE SUMMARY: WRKY transcription factors, a group of key regulators of many metabolic processes in plants, are now known to have a significant role in plant defense against sap-sucking insects such as aphids and whiteflies, but the molecular mechanisms underlying this plant defense is still poorly understood. In this study, we first showed that whitefly feeding and salicylic acid treatment of plants upregulate the expression of several WRKY transcription factors. We then showed that WRKYs’ contribution to plant defense is likely due to their interactions with the mitogen-activated protein kinase cascade (MAPK cascade) pathways in plants. Our findings contribute to a better understanding of the functions of WRKYs in plant defense against insect infestation. ABSTRACT: WRKY transcription factors are key regulators of many plant processes, most notably coping with biotic and abiotic stresses. Recently, the function of WRKY in plant defense against phloem-feeding insects such as whitefly (Bemisia tabaci) has been brought to attention. In this study, we found that the expression levels of Nicotiana tabacum WRKY4, WRKY6 and WRKY10 were significantly upregulated when tobacco plants were infested with whiteflies or treated with salicylic acid. Compared to controls, whiteflies lived longer and laid more eggs on NtWRKY-silenced tobacco plants but performed less well on NtWRKY-overexpressing plants. The three NtWRKYs interacted with five mitogen-activated protein kinases (NtMAPKs) in vivo and in vitro. These results suggest that the WRKYs in tobacco positively modulate plant defense against whiteflies through interaction with the mitogen-activated protein kinase cascade (MAPK cascade) pathways, and thus provide new insights into plant defense against phloem-feeding insects.