The Role of CLE Peptides in the Suppression of Mycorrhizal Colonization of Tomato

Signaling in Legume-Rhizobia Symbiosis

Legumes represent an important source of food protein for human nutrition and animal feed. Therefore, sustainable production of legume crops is an issue of global importance. It is well-known that legume-rhizobia symbiosis allows an increase in the productivity and resilience of legume crops. The efficiency of this mutualistic association strongly depends on precise regulation of the complex interactions between plant and rhizobia. Their molecular dialogue represents a complex multi-staged process, each step of which is critically important for the overall success of the symbiosis. In particular, understanding the details of the molecular mechanisms behind the nodule formation and functioning might give access to new legume cultivars with improved crop productivity. Therefore, here we provide a comprehensive literature overview on the dynamics of the signaling network underlying the development of the legume-rhizobia symbiosis. Thereby, we pay special attention to the new findings in the field, as well as the principal directions of the current and prospective research. For this, here we comprehensively address the principal signaling events involved in the nodule inception, development, functioning, and senescence.

Genome-Wide Identification and Characterization of CLAVATA3/EMBRYO SURROUNDING REGION (CLE) Gene Family in Foxtail Millet (Setaria italica L.)

The CLAVATA3/EMBRYO-SURROUNDING REGION (CLE) genes encode signaling peptides that play important roles in various developmental and physiological processes. However, the systematic identification and characterization of CLE genes in foxtail millet (Setaria italica L.) remain limited. In this study, we identified and characterized 41 SiCLE genes in the foxtail millet genome. These genes were distributed across nine chromosomes and classified into four groups, with five pairs resulting from gene duplication events. SiCLE genes within the same phylogenetic group shared similar gene structure and motif patterns, while 34 genes were found to be single-exon genes. All SiCLE peptides harbored the conserved C-terminal CLE domain, with highly conserved positions in the CLE core sequences shared among foxtail millet, Arabidopsis, rice, and maize. The SiCLE genes contained various cis-elements, including five plant hormone-responsive elements. Notably, 34 SiCLE genes possessed more than three types of phytohormone-responsive elements on their promoters. Comparative analysis revealed higher collinearity between CLE genes in maize and foxtail millet, which may be because they are both C4 plants. Tissue-specific expression patterns were observed, with genes within the same group exhibiting similar and specific expression profiles. SiCLE32 and SiCLE41, classified in Group D, displayed relatively high expression levels in all tissues except panicles. Most SiCLE genes exhibited low expression levels in young panicles, while SiCLE6, SiCLE24, SiCLE25, and SiCLE34 showed higher expression in young panicles, with SiCLE24 down-regulated during later panicle development. Greater numbers of SiCLE genes exhibited higher expression in roots, with SiCLE7, SiCLE22, and SiCLE36 showing the highest levels and SiCLE36 significantly down-regulated after abscisic acid (ABA) treatment. Following treatments with ABA, 6-benzylaminopurine (6-BA), and gibberellic acid 3 (GA3), most SiCLE genes displayed down-regulation followed by subsequent recovery, while jasmonic acid (JA) and indole-3-acetic acid (IAA) treatments led to upregulation at 30 min in leaves. Moreover, identical hormone treatments elicited different expression patterns of the same genes in leaves and stems. This comprehensive study enhances our understanding of the SiCLE gene family and provides a foundation for further investigations into the functions and evolution of SiCLE genes in foxtail millet.