Plant small RNAs (sRNAs) are pivotal regulators of gene expression, which are crucial in maintaining genome integrity and flexibility during development, abiotic and biotic stress responses. Current evidence suggests that sRNAs might be inherent to the sophisticated plant innate immune system battling bacteria. However, the role of sRNAs during antifungal plant defences is less clear. Therefore, this chapter investigates the sRNA‐mediated plant antifungal responses against the hemibiotrophic fungi Colletotrichum higginsianum and Colletotrichum graminicola in their respective compatible hosts Arabidopsis thaliana and Zea mays. A phenotypic and metabolomic analysis of A. thaliana sRNA mutants in response to C. higginsianum infection was performed, showing a hormonal and metabolic imbalance during fungal infection in these plants. To find whether fungal-induced sRNA could directly regulate defence genes in an agricultural important plant model, the expression of maize miRNAs in response to C. graminicola leaf and root infections was investigated. The results revealed the tissue‐specific local and systemic adaptation of the miRNA transcriptome, where only a few miRNAs were targeting defence pathways. The general picture presented here points towards a role of sRNAs as fine‐tuners of genetic and metabolomic defence response layers. This chapter also further discusses the potential of utilizing sRNA‐based fungal control strategies.
