24-Epibrassinolide Enhances Resistance Against Colletotrichum fructicola by Promoting Lignin Biosynthesis in Camellia sinensis L.

Brassinosteroids (BRs) are steroid-type phytohormones that not only control growth and development but also responses to biotic and abiotic stressors in plants. However, little is known about the function of BRs in the protection of tea against the fungal pathogen Colletotrichum fructicola causing anthracnose disease. Here, we revealed that 24-epibrassinolide (EBR) could improve tea resistance against C. fructicola, which was linked to the EBR-induced accumulation of lignin in tea leaves. Time-course of the relative expression of ITS/Cs18SrDNA showed that its expression increased after the inoculation with C. fructicola; however, EBR pretreatment significantly decreased the ITS/Cs18SrDNA expression at 3, 24 and 96 h postinoculation. Following an initial increase in 3 h postinoculation, lignin content significantly decreased from 6 to 24 h postinoculation with C. fructicola. In contrast to inoculation with only C. fructicola, exogenous EBR pretreatment significantly increased lignin contents throughout the postinoculation period. According to the qRT-PCR assay, EBR and C. fructicola differentially regulated the expression of 14 genes involved in the phenylpropanoid and lignin-specific pathways. Moreover, the activity of peroxidase (POD), a central enzyme in the final phase of lignin biosynthesis increased significantly at 3 h postinoculation with EBR treatment. Gene expression analysis revealed that EBR induced CsMYB4-like expression possibly to activate the transcription of CsPOD5-like gene responsible for lignin biosynthesis in response to C. fructicola. These findings suggest that EBR plays a positive role in disease resistance by inducing lignin synthesis, which may have potential application for the prevention of C. fructicola in tea plants. [ABSTRACT FROM AUTHOR]