Membrane-associated DELLA degradation modulates growth under carbon/nitrogen imbalance.

Crop yield and sustainability rely on the ability of plants to perceive and efficiently use nutrients. When high carbon (C) to nitrogen (N) ratios are perceived, plants trigger a specific response leading to reduced growth and enhanced anthocyanin accumulation. Here, using (Arabidopsis thaliana), we provide genetic, molecular and physiological evidence supporting a role for DELLA proteins to control growth under C/N stress through a non-nuclear mechanism that regulates their stability. C/N stress response specifically requires the RGA (REPRESSOR OF ga1-3 1) and GAI (GIBBERELLIC ACID INSENSITIVE) DELLA proteins, whose stability is reduced by a membrane-associated mechanism independent of the canonical gibberellic acid (GA)-GID1 (GIBBERELLIN INSENSITIVE DWARF1) pathway. Although C/N stress enhances DELLA accumulation by reducing GA levels, it also promotes their ubiquitination and degradation via interaction with the ATL31 E3-ligase at the membrane, even in the absence of GAs or when GA-resistant alleles are used. Moreover, phenotypic traits known to be altered by DELLA levels are not affected by enhanced ATL31 expression in the absence of stress. We propose that this mechanism fine-tunes DELLA-mediated C/N stress responses without adverse effects on plant development.