MaCDSP32, a bifunctional regulator of redox homeostasis and stage-dependent abiotic stress tolerance in Arabidopsis

Chloroplast-localized thioredoxin-like protein CDSP32 is induced by drought stress, but its integrated roles in abiotic stress tolerance and plant development remain elusive. Here, we investigated the function of MaCDSP32 from Morus alba by heterologous overexpression (OE) in Arabidopsis thaliana, combined with analyses of Atcdsp32 T-DNA insertion knock-down mutants (mt). MaCDSP32 was significantly induced by water deficit (triggered by heat or salt stress) but repressed by abscisic acid, salicylic acid, and ethephon, confirming osmotic rather than hormonal induction. OE of MaCDSP32 enhanced post-drought recovery with 100% survival rate, compared to only ~ 5% survival in mt and 86.67% in wild-type (WT). Under salt stress, mt exhibited a 45% reduction in chlorophyll content (p < 0.01), which was alleviated in OE lines. MaCDSP32 promoted H2O2 and O2− accumulation under drought and exert stage-specific regulation of antioxidant enzymes (SOD, POD, APX), with activities selectively elevated in OE lines during rewatering but not under drought or salt stress. This indicates that MaCDSP32 serves as a bifunctional regulator for redox homeostasis and stage-dependent abiotic stress tolerance. Additionally, MaCDSP32 OE significantly improved seed germination and seedling growth under osmotic stress (NaCl, mannitol, PEG). Notably, MaCDSP32 had no effect on stomatal aperture, confirming its function within the chloroplast redox microenvironment. In conclusion, MaCDSP32 acts as a chloroplast redox sensor that is indispensable for post-drought survival by coupling ROS signatures to stress recovery via antioxidant enzyme activation.