MdWRKY9 overexpression confers intensive dwarfing in the M26 rootstock of apple by directly inhibiting brassinosteroid synthetase MdDWF4 expression

Abstract

Dwarfing rootstocks enable high-density planting and are therefore highly desirable in modern apple (Malus domestica) production. M26 is a semi-dwarfing rootstock that is used worldwide, but identifying intensive dwarfing rootstock is a major goal of apple breeding programs. Herein, we show that MdWRKY9 mediates dwarfing by directly inhibiting the transcription of the brassinosteroid (BR) rate-limiting synthetase MdDWF4 and reducing BR production. We found that the transcriptional factor MdWRKY9 is highly expressed in all tested dwarfing rootstocks. Transgenic lines of M26 rootstock overexpressing MdWRKY9 exhibit further dwarfing, which resulted from the reduced BR levels and was reversed via exogenous brassinolide treatment. Both an in vivo chromatin immunoprecipitation (ChIP) analysis and an in vitro electrophoretic mobility shift assay (EMSA) indicated that MdWRKY9 binds to the promoter of MdDWF4. Furthermore, MdWRKY9 repressed MdDWF4 expression in stable transgenic apple plants as determined by quantitative PCR. In addition, RNA-interfered expression of MdWRKY9 in transiently transformed apple calli led to a significant increase of MdDWF4, suggesting MdWRKY9 plays a critical role in regulating the expression of MdDWF4. We report a novel dwarfing mechanism in perennial woody plants that involves WRKY-controlled BR production, and present a new dwarfing M26 rootstock for potential applications in apple production.

Identification of WRKY gene family and characterization of cold stress-responsive WRKY genes in eggplant

“…Several studies have confirmed that WRKY transcription factors are involved in hair development (Verweij et al, 2016), seed size (Luo et al, 2005;Gu et al, 2017), pollen development (Lei et al, 2017), growth types , flowering time , fruit ripening (Cheng et al, 2016) and leaf senescence (Ay et al, 2009;Brusslan et al, 2012;. WRKY transcription factors modulates plant hormone signaling pathways (Liu et al, 2017a;Liu et al, 2017b;Jin et al, 2018;Zheng et al, 2018). Despite the important roles in plant growth and development and signal pathways, the most significant function of WRKY proteins studied thoroughly and reported widely is transcription regulation of response to abiotic and biotic stresses.…”

Exogenous Brassinolide Alleviates Salt Stress in Malus hupehensis Rehd. by Regulating the Transcription of NHX-Type Na+(K+)/H+ Antiporters

“…The primers are shown in Table S1. The EMSA reaction was performed as described by Zheng et al (2018).…”

HD-ZIP I Transcription Factor (PtHB13) Negatively Regulates Citrus Flowering through Binding to FLOWERING LOCUS C Promoter

“…The yeast AH109 strain was transformed with pBD-PtFLC and pBD-PtHB13 constructs. The yeast transcriptional activity assay was performed as described previously [41]. Each experiment was independently repeated three times in this study.…”