Secretome analysis revealed amylases and peroxidases as markers of the early stages of somatic embryogenesis in Pinus nigra

Micropropagation of valuable conifer trees via somatic embryogenesis is efficient for rapid multiplication and preservation of germplasm. Suspension cell cultures are valuable tools to study extracellular proteins secreted into liquid cultivation medium, avoiding contamination from destructured cells. Extracellular proteins are essential regulators of somatic embryogenesis. Using a proteomic approach, we performed a pioneering study of the secretome of Pinus nigra cell lines with contrasting embryogenic capacity, accounting for variability between genotypes. Besides proteins affecting cell wall strength, such as four peroxidases and extensin, amylase and two basic secretory proteins accumulated in the medium from cell lines with high embryogenic capacity. In the medium of cell lines with low embryogenic capacity nuclease S1 and proteases were more abundant. These proteins are potentially involved in programmed cell death and nutrient recycling. Furthermore, two polygalacturonases and expansin correlated with microscopic observations. Validating proteomic findings, we tested the peroxidase and amylase activity in the medium of several cell lines. We concluded that both tested enzyme activities may be considered potential markers of high embryogenic capacity.