Time course metabolomics and 13CO2 mapping establish BBX31/miP1b mediated metabolic readjustments conferring UV-B tolerance in Arabidopsis

B-box proteins (BBXs) are transcription factors that act as signal transducers in light signaling pathways. The microprotein BBX31/miP1b is known to play a positive role in promoting photomorphogenesis and stress tolerance under UV-B. However, the BBX31-mediated metabolic reprogramming to confer UV-B tolerance in plants is not well characterised. Here, we integrate metabolomics with kinetic 13CO2 tracer-based metabolic mapping, morpho-physiological and biochemical analysis to determine the metabolic rewiring in the UV tolerant genotypes. Our results suggest that BBX31 modulates the levels of photosynthetic compounds, reduces TCA cycle intermediates and enhances GS/GOGAT metabolic intermediates and secondary metabolic pathways. 13CO2 tracing studies established BBX31 modulates phenylpropanoid and GS/GOGAT pathways to divert flux towards the accumulation of UV-B protective metabolites phenylalanine, oxoproline, glutamine, and others. Although metabolomics indicated a higher accumulation of branch chain amino acids (BCAAs) under UV-B, they had negligible 13C incorporation, indicating their biosynthesis from pre-existing intermediates or via protein degradation. Further, we demonstrate that the exogenous application of phenylalanine, identified as one of the marker metabolites, confers tolerance to plants under UV-B. This study sheds light on BBX31-mediated metabolic rewiring under UV-B, which can assist targeted enrichment of metabolites and metabolic engineering to promote UV-B tolerance in plants. HighlightBBX31/miP1b modulates the levels of photosynthetic compounds, reduces TCA cycle intermediates and enhances GS/GOGAT metabolic intermediates to confer UV-B tolerance.