Ectopic expression of ARGOS8 reveals a role for ethylene in root‐lodging resistance in maize

Summary Ethylene plays a critical role in many diverse processes in plant development. Recent studies have demonstrated that overexpression of the maize ARGOS8 gene reduces the plant's response to ethylene by decreasing ethylene signaling and enhances grain yield in transgenic maize plants. The objective of this study was to determine the effects of ethylene on the development of nodal roots, which are primarily responsible for root‐lodging resistance in maize. Exogenous application of the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid (ACC) was found to promote the emergence of nodal roots. Transcriptome analysis of nodal tissues revealed that the expression of genes involved in metabolic processes and cell wall biogenesis was upregulated in response to ACC treatment, supporting the notion that ethylene is a positive regulator for the outgrowth of young root primordia. In BSV::ARGOS8 transgenic plants with reduced ethylene sensitivity due to constitutive overexpression of ARGOS8, nodal root emergence was delayed and the promotional effect of ACC on nodal root emergence decreased. Field tests showed that the BSV::ARGOS8 plants had higher root lodging relative to non‐transgenic controls. When ARGOS8 expression was controlled by the developmentally regulated promoter FTM1, which conferred ARGOS8 overexpression in adult plants but not in the nodal roots and nodes in juvenile plants, the FTM1::ARGOS8 plants had no significant difference in root lodging compared with the wild type but produced a higher grain yield. These results suggest that ethylene has a role in promoting nodal root emergence and that a delay in nodal root development has a negative effect on root‐lodging resistance in maize. Significance StatementRoot‐lodging resistance is a critically important trait for high‐yield maize hybrids and has been selected in maize breeding programs over the past 100 years. In maize, the stem‐borne nodal roots are formed in the normal developmental process and play a major role in root‐lodging resistance. Using the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and ARGOS8 transgenic plants which have reduced ethylene sensitivity, we found that ACC promotes nodal root emergence and that ARGOS8 transgenic plants have delayed nodal root development and increased root lodging. These results suggest a positive role for ethylene in root‐lodging resistance. These findings have applications in maize breeding for improved agronomic traits.