HHO5 orchestrates feedback regulation between organic and inorganic N-dose dependent signaling in Arabidopsis; DoubleTARGET

Important regulators of plant N-responses include the HRS1 HOMOLOG (HHO) transcription factors (TFs), yet their redundant repressive mode of action has hindered functional analyses. Here, we highlight HHO5 as a unique HHO TF based on its phylogenetic position, phloem specific expression, and its dual role in orchestrating responses to both inorganic and organic N-dose signals.

Moreover, single hho5 T-DNA mutants show reduced N-dose dependent growth, and decreased seed N content, indicating phenotypic defects in systemic N-dose responses. Our meta-analysis revealed that HHO5 expression is repressed by nitrate but induced by organic N treatments. To uncover its mode of action, we derived a validated HHO5 gene regulatory network path in which the direct and indirect targets of HHO5 encompass ~12% of all N-dose response genes in planta.