Characterization and Transcriptomic Analysis of Sorghum EIN/EIL Family and Identification of Their Roles in Internode Maturation

Ethylene-insensitive 3/Ethylene-insensitive3-like proteins (EIN3/EIL) represent a group of transcription factors critical for the ethylene signaling transduction that manipulate downstream ethylene-responsive genes, thereby regulating plant growth, development, and stress responses. However, the identification, evolution, and divergence of the EIL family remain to be studied in <i>Sorghum bicolor</i>. Here, we identified eight <i>SbEIL</i>s, which were expanded due to whole-genome-duplication (WGD) events. Characterization of the protein sequences and expression atlas demonstrates that the WGD-duplicated <i>SbEIL</i>s could become divergent due to the differential expression patterns, rather than domain and motif architectures. Comparative expression analysis was performed between the RNA-seq data sets of internodes from several sorghum cultivars to understand the potential roles of SbEIL members in internode elongation and maturation. Our results identified <i>SbEIL3</i> and <i>7</i> (the latter as a homolog of <i>OsEIL7/OsEIL1</i>) to be the highly expressed <i>SbEIL</i> genes in sorghum internodes and revealed a potential functional link between <i>SbEIL7</i> and internode maturation. The co-expression analysis and comparative expression analysis with ethylene-regulated gene sets found that <i>SbEIL7</i> was co-regulated with a set of ubiquitin-related protein degradation genes, suggesting possible involvement of SbEIL7 in protein degradation and processing during the post-anthesis stages. Altogether, our findings lay a foundation for future functional studies of ethylene signaling-mediated gene regulation and improvement of sorghum internode development.