Functional characterization of lactate metabolism and its key regulatory genes reveals lactate-mediated modulation of carbon and nitrogen metabolism in Phaeodactylum tricornutum.

BACKGROUND: The marine diatom Phaeodactylum tricornutum plays a crucial role in global carbon and nitrogen cycling. Previous work revealed that lactate regulates carbon and nitrogen metabolism of P. tricornutum through protein lactylation, significantly affecting growth characteristics, photosynthetic efficiency, biochemical composition, and expression of genes related to carbon and nitrogen metabolism. However, the functional roles of lactate metabolism genes and their regulatory mechanisms in carbon-nitrogen homeostasis remain unexplored. This study aimed to characterize key lactate metabolism and regulatory genes (ldhA, Glo1, Glo2, D-LCR, GlxI, and GPCR) and elucidate their influence on carbon and nitrogen metabolic modulation in P. tricornutum. RESULTS: Overexpression (OE) and RNA silence (AS) of ldhA, Glo1, Glo2, D-LCR, GlxI, and GPCR revealed their roles in lactate metabolism and regulation. The overexpression of Glo2 and ldhA enhanced exogenous lactate utilization and total lipid accumulation under low nitrogen (LN) conditions. Additionally, the overexpression of Glo1 and D-LCR facilitated the utilization of exogenous lactate to cope with LN conditions. In contrast, the growth and L-lactate consumption rates of GlxI and GPCR overexpression strains were significantly lower than or not significantly different from those of the WT strain. The key enzyme involved in lactate metabolism, LDHA, was selected for further functional analysis. Western blot analysis suggested that ldhA overexpression promoted the lactylation of an approximately 40 kDa lactylated protein in P. tricornutum. 13C-labeling analysis demonstrated that ldhA overexpression in P. tricornutum accelerated lactate utilization and the processes of glycolysis, TCA cycle, CCM, and Calvin cycle. RNA-Seq analysis revealed that ldhA overexpression promoted cell division metabolism and lipid metabolism in P. tricornutum under LN conditions and glycerophospholipid metabolism under exogenous lactate addition conditions. CONCLUSION: Lactate metabolism and lactylation metabolic processes mediated by LDHA, GLO1, GLO2 and D-LCR are important mechanisms by which lactate affects the growth of P. tricornutum, rapidly regulates carbon and nitrogen metabolism processes, and promotes the accumulation of lipids under LN conditions.