TaWRKY51 promotes lateral root formation through negative regulation of ethylene biosynthesis in wheat (Triticum aestivum L.)

Common wheat (Triticum aestivum L.) is an important staple food crop worldwide. Lateral roots (LRs), as the major component of root architecture, affect water and nutrient uptake in wheat. The phytohormone ethylene is known to affect LR formation; however, the factor(s) modulating ethylene during this process have not yet been elucidated in wheat. Here we identified wheat TaWRKY51 as a key factor that functions in LR formation by modulating ethylene biosynthesis. Wheat TaWRKY51RNA interference lines (TaWRKY51-RNAi) and the homozygous mutants tawrky51-2a and tawrky51-2b all produced fewer LRs than the wild type and negative transgenic plants, whereas the TaWRKY51 overexpression lines (TaWRKY51-OE) had the opposite phenotype. Transcription analysis revealed that 1-aminocyclopropane-1-carboxylic acid synthase (ACS) genes (TaACS2, TaACS7 and TaACS8) involved in ethylene biosynthesis were downregulated in TaWRKY51-OE lines but upregulated in TaWRKY51-RNAi lines. The rate of ethylene production also decreased in TaWRKY51-OE lines but increased in TaWRKY51-RNAi lines compared with their respective negative transgenic controls. Electrophoretic mobility shift and transient expression assays revealed that TaWRKY51 inhibits the expression of ACS genes by binding to the W-box cis-element present in their promoter region. Moreover, overexpression of ACS2 or exogenous application of 1-aminocyclopropane-1-carboxylic acid reversed the phenotype of enhanced LR number in TaWRKY51-OE Arabidopsis lines, and overexpression of TaWRKY51 in the ethylene-overproducing mutant eto1-1 rescued its LR defect phenotype. In addition, genetic evidence demonstrates that TaWRKY51-regulated LR formation is also dependent on ethylene and auxin signaling pathways. Our findings reveal a molecular genetic mechanism by which a WRKY gene coordinates ethylene production and LR formation in wheat. Significance Statement Ethylene is known to affect lateral root formation, but the factor(s) modulating ethylene during this process have not yet been identified in wheat. In this study we identify wheat WRKY51 as a key factor that functions in lateral root formation by modulating ethylene biosynthesis by directly targeting the ethylene synthesis genes.