Overexpression of OsMBL1 Is Associated with Changes in Flavonoid Biosynthesis and Antioxidant Capacity in Rice

Plant-derived lectins originating from plants perform essential functions in both plant growth and stress response processes. Rice jacalin-related mannose-binding lectin 1 (OsMBL1), a well-characterized canonical salt-responsive regulatory factor, acts as a core positive regulator that confers enhanced salt tolerance. In the present study, OsMBL1 was found to respond to multiple environmental stresses and signaling molecules, and it not only positively regulated salt tolerance at the seedling stage but also at the seed germination stage. To dissect the underlying regulatory network, we performed transcriptome profiling of an OsMBL1-overexpressing line, which identified 562 differentially expressed genes (438 up- and 124 down-regulated) relative to wild-type plants. These sets of differentially expressed genes exert pivotal control over a suite of physiological events, most notably the conserved metabolic routes of phenylpropanoid and flavonoid biosynthesis. Further physiological assays confirmed a low level of membrane lipid peroxidation and a high level of flavonoids and ascorbate peroxidase (APX) and peroxidase antioxidant enzyme activities in the OsMBL1-overexpressing line. Collectively, these correlative findings suggest that OsMBL1 overexpression is associated with the upregulation of genes involved in flavonoid biosynthesis and with an altered antioxidant system status, which may contribute to enhanced stress tolerance in rice. Collectively, these observations provide a deeper perspective on the molecular underpinnings of OsMBL1-associated stress adaptation.