bioRxiv · 2026-05-02
Scientists discovered a protein in Arabidopsis (thale cress) that acts as a traffic controller for riboflavin (vitamin B2), steering how much of it reaches flowers, seed pods, and seeds. Without this protein, riboflavin over-accumulates in reproductive organs — revealing that plants actively regulate where this essential nutrient goes, rather than letting it diffuse freely.
AtPUP5, a plasma membrane protein, transports riboflavin and (less efficiently) FMN into cells, but struggles to move FAD, suggesting selectivity among related vitamin B2 forms.
Plants lacking AtPUP5 accumulate excess riboflavin specifically in reproductive organs — flowers, seed pods, and seeds — regardless of whether extra riboflavin was supplied externally.
AtPUP5 is not required for whole-plant riboflavin uptake, showing its role is spatially specific: local redistribution within reproductive tissues, not global absorption.
