Quantitative Proteomics of Maize Roots Treated with a Protein Hydrolysate: A Comparative Study with Transcriptomics Highlights the Molecular Mechanisms Responsive to Biostimulants

Protein
hydrolysate (PH)-based biostimulants offer a cost-effective
and sustainable approach for the regulation of physiological processes
in plants to stimulate growth and improve stress tolerance. Understanding
the mode of action of PHs is challenging, but it is indispensable
to improve existing candidates and to develop novel molecules with
enhanced stimulatory effects. Hence, the present study aimed to understand
the proteome level responses in the B73 maize roots treated with APR,
a PH biostimulant, at two increasing concentrations and to compare
and integrate it with the transcriptomic data obtained previously
under identical experimental conditions. Results indicate that APR
induced dose-dependent global changes in the transcriptome and proteome
of maize roots. APR treatment altered the expression and abundance
of several genes and proteins related to redox homeostasis, stress
response, glycolysis, tricarboxylic acid cycle, pentose phosphate
pathway, and other metabolic pathways of carbohydrates, amino acids,
and lipids. Further, metabolic processes of phytohormone, secondary
metabolites, especially phenylpropanoids, flavonoids, and terpenoids
and transport, and cytoskeletal reorganization associated mechanisms
were stimulated. Our results suggest that APR treatment altered the
redox homeostasis and thus triggered an oxidative signal. This could
be one of the key regulators of the cascade of downstream events involving
multiple signaling, hormonal, and metabolic pathways, resulting in
an altered physiological and metabolic state which consequently could
lead to improved growth and stress adaptation observed in biostimulanttreated
plants.