The crosstalk between UV-B abiotic stress and flg22 biotic stress has been previously reported in Arabidopsis thaliana, both in cell cultures and seedlings (Schenke et al., 2011; Zhou et al., 2017). However, to date, no study has been conducted whether this crosstalk is also work in the Brassica napus. Therefore, the seedlings of Brassica napus were treated as explained in material and method part. Each biological replicate consists of 4 seedlings (leaves only) pooled for RNA extraction which includes 4 treatments Water/VIS-light control (C), flg22 treatment (F), UV-B treatment (U) and the co-treatment flg22 and UV-B (F/U).
As explained before, CHS holds an important role in Flavonoid pathway. Supported by GENEVESTIGATOR perturbation result, CHS appears to be strongly induced by UV-B and suppressed by various biotic stress treatment (Supplementary picture 1). In this case of crosstalk, Schenke et al. (2011) has proposed utilization of CHS as a marker gene.
Through this study, the crosstalk between UV-B and flg22 in Brassica napus proved to be relevant and functional. Following its CHS gene level expression, CHS gene expression level appeared to be highly induced after 4 h of UV-B Exposure treatment, indicating a higher production of the flavonoid compounds. On the other hand, the CHS gene was suppressed in plants treated with flg22 alone. Flg22 was found to have an inhibitory effect on UV-B induced flavonoids biosynthesis as the concomitant of flg22 in plant treated with UV-B lead to a repression of the CHS gene-level expression. This phenomenon has been explained before in case of Arabidopsis thaliana, as Schenke and Cai (2014) reveal when the plant challenged with UV-B and flg22, it would consider the threat from pathogen much more threatening than the UV-B. The plant would swift its metabolites production from flavonoids to a compound that much more beneficial for inhibiting the spreading of the pathogen, e.g. lignin and scopoletin which come from the same phenylalanine precursor.