Functional omics identifies serine hydrolases that mobilize storage lipids during rice seed germination.

Elucidating proteolipidome dynamics is crucial for understanding the roles of these
molecules in plant physiology and disease. Sequence-based functional annotation of the
protein is inadequate since protein activities depend on post-translational modification. In the
present study, we applied a gel-free activity-based protein profiling (ABPP) approach to
unravel the active lipases, including other serine hydrolases (SHs), expressed during seed
germination in rice (Oryza sativa). We successfully mapped the active sites of 43 active SHs
encompassing lipases/esterases, GDSL lipases, proteases, serine carboxypeptidases, ABHD
protein, pectin acetylesterase, and other SHs. The mRNA expression levels of those genes
encoding the identified SHs were monitored using microarray analysis. The lipidome analysis
revealed distinct patterns of molecular species distribution in individual lipid classes and
displayed the metabolic connections between lipid mobilization and rice seedling growth.
Changes in the mobilization of storage lipids and their molecular species remodeling were
correlated with the expression of the identified lipases and their lipase activity in a time36 dependent manner. The physiological significance of the identified SHs was explored during
biotic stress with Fusarium verticilloides infection. The fungal infection significantly reduced
lipase activity and lipid mobilization, thus impairing the rice seedling. Collectively, our data
demonstrate application of the functional proteome strategy along with the shotgun lipidome
approach for the identification of active SHs, and thus for deciphering the role of lipid
homeostasis during rice seed germination.