<scp>OsWRKY18</scp> attenuates proteasomal degradation of <scp>OsbZIP48</scp> to orchestrate zinc homeostasis in rice

Zinc (Zn) is an essential micronutrient for plants, and its deficiency in soils severely limits crop yield and grain nutritional quality. While the F-bZIP transcription factor OsbZIP48 is known to play a central role in maintaining Zn homeostasis in rice, the post-translational mechanisms that regulate its activity remain elusive. Here, we identify the WRKY transcription factor OsWRKY18 as a key post-translational regulator of OsbZIP48. Through a combination of molecular, genetic, biochemical, and physiological approaches, we characterized the function of OsWRKY18 and its role in modulating the OsbZIP48 protein stability to regulate Zn homeostasis. We show that OsWRKY18 expression is specifically induced under Zn-limiting conditions. Loss-of-function mutants (oswrky18) exhibited heightened sensitivity to Zn deficiency and a significant reduction in Zn accumulation in the shoots. Mechanistically, OsWRKY18 directly interacts with OsbZIP48. This physical interaction protects OsbZIP48 from proteasome-mediated degradation, thereby enhancing its protein stability. Consequently, OsWRKY18 potentiates the transcriptional activation of key Zn transporter genes, including OsZIP4 and OsZIP8, which are crucial for Zn translocation and distribution to developing tissues. Our findings reveal a novel regulatory module wherein OsWRKY18 stabilizes OsbZIP48 to orchestrate the expression of Zn transporters, providing significant insights into the post-translational regulatory mechanisms of micronutrient homeostasis in plants.