Rapeseed NTL4 transcription factor positively regulates leaf senescence and resistance against bacterial pathogen via controlling transcription of ROS and SA biosynthetic genes

Abstract

Rapeseed (Brassica napus L.) is widely planted for both edible oil and biodiesel. However, its growth is frequently affected by adverse environmental factors such as pathogens. Moreover, rapeseed shows significant falling of leaves during the whole growth period, making it important to control leaf senescence for better nutrient utilization efficiency and improved growth. Membrane-tethered transcription factors (MTTF) constitute a special group of proteins, which facilitate rapid response to adverse conditions. However, the role of MTTFs in rapeseed has seldomly been reported. Here BnaNTL4 was functionally characterized to transcriptionally regulate leaf senescence and resistance towards a bacterial pathogen in rapeseed. BnaNTL4 encodes a member-associated transcription factor and its expression was induced by several stimuli including salicylic acid and hydrogen peroxide. Both stable and transient expression demonstrated BnaNTL4 could induce reactive oxygen species (ROS) production and leaf chlorosis. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assay of differentially expressed genes in BnaNTL4 overexpression lines and control plants uncovered that several genes related to programmed cell death (γVPE, BFN1), ROS production (RbohF), salicylic acid (SA) synthesis (PBS3) and senescence (SEN4) were induced by BnaNTL4 overexpression. Further, a dual luciferase reporter assay revealed BnaNTL4 transactivated the activities of the promoters of putative target genes. At last, an electrophoretic mobility shift assay discovered that BnaNTL4 directly bound to promoters of BnaRbohF, BnaPBS3 and BnaSEN4. Overexpression of BnaNTL4 also enhances resistance towards a bacterial pathogen Pseudomonas syringae DC3000. Thus, the results uncovered a dual role of BnaNTL4 in leaf senescence and disease resistance in rapeseed.