Objective Functions in responses to abiotic stress and antioxidant regulation of bZIP34 in Manihot esculenta, an important tropical food crop prone to postharvest shelf life-shortening discoloration, were studied.

Methods Coding sequence of MebZIP34 was cloned from the storage roots of M. esculenta SC8. Bioinformatics analysis was performed to determine the protein structure, conserved motif, phylogenetic tree, and promoter cis-elements of the gene. An overexpression vector was constructed and transiently expressed in cassava leaves to examine its regulatory effect on the downstream antioxidant gene MeMDAR1. Transgenic Arabidopsis lines with overexpressed MebZIP34 were generated to assess the physiological indicators of antioxidant capacity.

Results The full-length CDS of MebZIP34 was 975 bp encoded a 324-amino-acid protein containing a typical bZIP domain and the structure consisting primarily of α-helices and random coils. Phylogenetically, it closely related to Hevea brasiliensis. Its promoter expression was regulated by multiple cis-acting elements associated with light, hormonal signaling, and stress responses. Transient expression of the gene significantly upregulated MeMDAR1, enhanced SOD, and reduced MDA. Similar phenomena were observed in the MebZIP34-overexpressed Arabidopsis as well, which confirmed the role of the gene in regulating antioxidation of the plant. It also exhibited relatively high levels of expression in organized embryogenic structures and shoot apical meristem, but moderate in vegetative organs, such as fibrous roots, storage roots, and stems.

Conclusion A bZIP transcription factor, MebZIP34 had a conserved structure and functions that enhanced the plant antioxidant capacity by regulating the downstream gene expression. It displayed significant potential for applications in cassava post-harvest preservation and breeding stress-resistant varieties with prolonged shelf life.