Abstract
Anthracnose, a severe disease caused by Colletotrichum, affects diverse crops and leads to significant economic losses through pronounced fruit/leaf lesions. MicroRNAs (miRNAs) play crucial roles in modulating gene expression in response to disease resistance, defence responses and plant immunity. However, the regulatory mechanisms of miRNAs in responses to Colletotrichum gloeosporioides remain unknown in tea plants. Our study revealed that csn-miR393a targets auxin receptor gene CsAFB2 during resistance to C. gloeosporioides in tea plants by comparing the resistant cultivar Zhongcha108 to the susceptible cultivar Longjing43. Through Nicotiana benthamiana leaf co-transformation assays, we demonstrated that csn-miR393a suppresses the expression of CsAFB2, and csn-miR393a target mimic blocks the function of csn-miR393a, leading to increase in the expression of CsAFB2. Repression of transcripts in tea leaves by antisense oligonucleotides demonstrated that csn-miR393a negatively affects the tea plant defence by regulating reactive oxygen species homoeostasis, PR gene expression and catechin accumulation. To further validate the regulatory mechanisms of csn-miR393a, we developed transgenic tea plants overexpressing CsAFB2, resulting in enhanced resistance responses against C. gloeosporioides. Additionally, transgenic N. benthamiana lines overexpressing a csn-miR393a target mimic provided further evidence that csn-miR393a negatively regulates the tea plant defence response against C. gloeosporioides by suppressing CsAFB2. Therefore, manipulating csn-miR393a or its target gene, CsAFB2, has the potential to strengthen the tea plant's resistance against tea anthracnose.