Transcriptome profiling of nla-mutant Arabidopsis reveals possible post-translational regulation of key factors cross-linking circadian-rhythm and anthocyanin pathways under boron toxicity

Understanding molecular responses against boron (B) stress is one of the goals for improving excess B management of cereals. Since earlier findings demonstrated the differential regulation of protein degradation genes under B toxicity, this study focused on the interaction between toxic B responsive regulations and Nitrogen Limitation Adaptation (NLA) gene encoding an E3 ubiquitin ligase. Therefore, WT and nla mutant Arabidopsis thaliana plants were grown under mild and moderate levels of B toxicity and RNA sequencing was performed in these plants. Accordingly, ribosome was overrepresented for upregulated genes in nla mutants under all conditions when compared to WT whereas alpha-linolenic acid metabolism, plant-pathogen interaction and MAPK signaling pathways were downregulated. Inhibition of glucosinolate biosynthesis and induction of phenylpropanoid pathway as well as enrichment of circadian rhythm were among the most prominent results for B-stressed nla mutants compared to nla mutant Arabidopsis under control condition (C). Interestingly, unlike WT, B-induced accumulation of anthocyanin was not observed in nla mutants. This was attributed to switching from flavonoid to lignin biosynthesis in the phenylpropanoid pathway. Also, the impairment of crosstalk between circadian rhythm and anthocyanin pathways might explain this phenomenon because two pathways are crosslinked by ORE1, one of the targets of NLA.