Melon shoot organization 1, encoding an AGRONAUTE7 protein, plays a crucial role in plant development

Key message A melon gene MSO1 located on chromosome 10 by map-based cloning strategy, which encodes an ARGONAUTE 7 protein, is responsible for the development of shoot organization. Plant endogenous small RNAs (sRNAs) are involved in various plant developmental processes. In Arabidopsis, sRNAs combined with ARGONAUTE (AGO) proteins are incorporated into the RNA-induced silencing complex (RISC), which functions in RNA silencing or biogenesis of trans-acting siRNAs (ta-siRNAs). However, their roles in melon (Cucumis melo L.) are still unclear. Here, the melon shoot organization 1 (mso1) mutant was identified and shown to exhibit pleiotropic phenotypes in leaf morphology and plant architecture. Positional cloning of MSO1 revealed that it encodes a homologue of ArabidopsisAGO7/ZIPPY, which is required for the production of ta-siRNAs. The AG-to-C mutation in the second exon of MSO1 caused a frameshift mutation and significantly reduced its expression. Ectopic expression of MSO1 rescued the Arabidopsisago7 phenotype. RNA-seq analysis showed that several genes involved in transcriptional regulation and plant hormones were significantly altered in mso1 compared to WT. A total of 304 and 231 miRNAs were identified in mso1 and WT by sRNA sequencing, respectively, and among them, 42 known and ten novel miRNAs were differentially expressed. cme-miR390a significantly accumulated, and the expression levels of the two ta-siRNAs were almost completely abolished in mso1. Correspondingly, their targets, the ARF3 and ARF4 genes, showed dramatically upregulated expression, indicating that the miR390-TAS3-ARF pathway has conserved roles in melon. These findings will help us better understand the molecular mechanisms of MSO1 in plant development in melon.

Automated summary

By cloning and functional analysis of the melon MSO1 gene, it was found that this gene encodes an ARGONAUTE 7 protein, which plays an important role in the development of melon. The study also found that small RNAs and miRNAs in melon play important roles in regulating plant development.