Arabidopsis Nuclear Architecture related 1 facilitates the floral transition in a process involving molecular...

Although emerging evidence revealed that molecular hydrogen (H₂) positively regulates numerous physiological responses, understanding the synthesis of H₂ and its functions is a challenge for biology.

The correct timing of flowering is controlled by environmental stimuli and endogenous signals. We report that endogenous H₂ facilitates the floral transition in Arabidopsis.

The Nuclear Architecture Related 1 (NAR1) gene of Arabidopsis was prokaryotic expressed and purified, and its H₂-synthesizing activity was subsequently detected. Furthermore, mutation experiments were used to investigate the catalytic roles of conserved sequences and Cys sites. Biochemistry and molecular approaches were employed to investigate the role of H₂ in regulating floral transition.

Similar to [Fe-Fe] hydrogenase (HYD1) from Chlamydomonas reinhardtii, NAR1 protein is a H₂-synthesizing enzyme in Arabidopsis thaliana. Protein mutation experiments in vitro show that four Cys residues are important for the inducible catalyzing activity upon hypoxia. Accordingly, NAR1-dependent circadian-rhythmic H₂ was observed under light/dark cycles, which was accompanied with contrasting changes in nitric oxide (NO) signal. Knockdown of NAR1 by CRISPR or RNAi reduced H₂ production and delayed flowering. Whereas, exogenous H₂ supply and overexpressing NAR1 or CrHYD1 promoted early flowering. These early flowering phenotypes were aggravated by the removal of endogenous NO, but abolished by NO addition. Since the mutant (mms19) defective in Fe-S cluster assembly function displays early flowering regardless of H₂ addition, we further deduce that NAR1 control of early flowering is largely achieved by H₂.

Biochemical and genetic evidences show that NAR1-driven floral transition is functionally linked to the modulation of circadian oscillators via NO signaling. Since H₂ production is modulated by circadian rhythms and constitutively produced, it may integrate external and internal cues into floral transition, and the modulation of its production might be a promising strategy for crop breeding cultivation.