Sdf2, or stromal cell-derived factor 2, is an endoplasmic reticulum (ER)-resident protein. It belongs to the SDFs family, and has a paralogous gene Sdf2l1 in human and mouse with 78% similar protein sequences [2]. Sdf2 is implicated in the unfolded protein response (UPR) pathway when ER stress occurs due to misfolded protein accumulation in the ER lumen [1,2,3]. It also plays a role in protein quality control as it is part of the BiP chaperone cycle, preventing protein aggregation [5].

In rice, silencing of Sdf2 genes in the XA21 rice genetic background compromises resistance to the Gram-negative bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo), indicating its importance in XA21-mediated immunity [4]. In Arabidopsis, Sdf2 is crucial for the UPR, and its mutants display strong defects during seedling development under ER stress conditions [3]. Also, the double mutation of Sdf2 and ER (ERECTA) gene in Arabidopsis results in defects in the inner integument, suggesting the Sdf2-ERdj3B-BiP chaperone complex might control the translocation of ERECTA-family proteins from the ER to the plasma membrane [7].

In conclusion, Sdf2 is essential for maintaining ER homeostasis through its involvement in the UPR and protein quality control. Its functions have been revealed through studies in various genetic models like rice and Arabidopsis, highlighting its importance in plant immunity and development. In the context of human diseases, its potential role in conditions related to ER stress such as severe preeclampsia, labor-onset, and osteoporosis is being explored [1,6].