Effective enhancement of resistance to Phytophthora infestans by overexpression of miR172a and b in Solanum lycopersicum

Main conclusion Overexpression of miR172a and b in tomato ( Solanum lycopersicum ) Zaofen No. 2 increased resistance to Phytophthora infestans infection by suppressing of an AP2/ERF transcription factor. The miR172 family has been shown to participate in the growth phase transition, flowering time control, abiotic and biotic stresses by regulating the expression of a small group of AP2/ERF transcription factors. In this study, the precursors of miR172a and b were cloned from tomato, Solanum pimpinellifolium L3708. We used the degradome sequencing to determine the cleavage site of miR172 to a member of the AP2/ERF transcription factor family (Solyc11g072600.1.1). qRT-PCR results showed that the expression of AP2/ERF was negatively correlated with the expression of miR172 in S. pimpinellifolium L3708 infected with Phytophthora infestans. Overexpression of miR172a and b in S. lycopersicum Zaofen No. 2 conferred greater resistance to P. infestans infection, as evidenced by decreased disease index, lesion sizes, and P. infestans abundance. The SOD and POD play important roles in scavenging late massive ROS in plant–pathogen interaction. Malonaldehyde (MDA) is widely recognized as an indicator of lipid peroxidation. Membrane damage in plants can be estimated by measuring leakage of electrolytes, which is evaluated by determining relative electrolyte leakage (REL). Less H2O2 and O2 −, higher activities of POD and SOD, less MDA content and REL, and higher chlorophyll content and photosynthetic rate were also shown in transgenic plants after inoculation with P. infestans. Our results constitute the first step towards further investigations into the biological function and molecular mechanism of miR172-mediated silencing of AP2/ERF transcription factors in S. lycopersicum–P. infestans interaction and provide a candidate gene for breeding to enhance biotic stress-resistance in S. lycopersicum.