MAIN CONCLUSION: miR477 acts as a negative regulator in
tea plant immunity against Pseudopestalotiopsis
infection by repressing the expression of its target gene PAL.
MicroRNA (
miRNA)-mediated post-transcriptional regulation plays a fundamental role in various plant physiological processes, including responses to pathogens. Our previous research revealed that miR477 might be involved in the
tea plant-Pseudopestalotiopsis interaction (data not shown). In the present study, the accumulation of miR477 significantly decreased in
tea plants during Pseudopestalotiopsis species
infection. Using
miRNA and degradome data sets, the targeting of
phenylalanine ammonia-lyase (PAL) by miR477 was validated by 5' RLM-RACE. GUS assay showed that the expression of PAL was post-transcriptionally regulated by miR477 and silenced by
mRNA cleavage. A negative correlation between the expression of miR477 and PAL was found in
tea plants infected by the pathogen. The transgenic lines overexpressing Csn-miR477 exhibited increased susceptibility to Pseudopestalotiopsis species, which was associated with reduced expression of PAL during
infection. The degree of severity of the leaf lesions and the results of
trypan blue staining showed that the plants overexpressing Csn-miR477 exhibited more severe damage upon pathogen
infection than wild-type plants. In addition, more H2O2 and O2-, higher
malondialdehyde (MDA) contents and less
superoxide dismutase (SOD) and
peroxidase (POD) activities were detected in the transgenic plants than in the wild-type plants after inoculation with Pseudopestalotiopsis species. Taken together, our results implied that Csn-miR477 might act as a negative regulator in pathogen-infected
tea plants by inhibiting the expression of its target, PAL, and that Csn-miR477 is a candidate
miRNA for improving the adaptation of
tea plant to disease.