Embryogenic competence acquisition in sugarcane callus is associated with differential H+ pump abundance and activity

Somatic embryogenesis is an important biological process in several plant species, including sugarcane. Proteomics approaches have shown that H+ pumps are differentially regulated during somatic embryogenesis; however, the relationship between H+ flux and embryogenic competence is still unclear. This work aimed to elucidate the association between extracellular H+ flux and somatic embryo maturation in sugarcane. We performed a microsomal proteomics analysis and analyzed changes in extracellular H+ flux and H+ pump (P-H+-ATPase, V-H+-ATPase and H+-PPase) activity in embryogenic and non-embryogenic callus. A total of 657 proteins were identified, 16 of which were H+ pumps. We observed that P-H+-ATPase and H+-PPase were more abundant in embryogenic callus. Compared with non-embryogenic callus, embryogenic callus showed high H+ influx, especially at maturation day 14 as well as higher H+ pump activity, mainly P-H+-ATPase and H+-PPase activity. The H+-PPase appears to be the major H+ pump in embryogenic callus during somatic embryo formation, functioning in both vacuole acidification and PPi homeostasis. These results provide evidence for an association between higher H+ pump protein abundance and, consequently, higher H+ flux and embryogenic competence acquisition in the callus of sugarcane.