Storage lipid mobilization pathways during pollen germination in Olea europaea

Abstract

Organelles called oil bodies (OBs), which are gradually mobilized during pollen germination. Our current knowledge regarding the molecular mechanisms that regulate OB mobilization in the pollen tube is scarce. In this work, we characterized severa! OB-associated enzymes involved in storage lipid breakdown. First, we showed that phospholipase A (PLA) and peroxygenase (PX) proteins were early incorporated during OB biogenesis, whereas acyllipase (LIP) and lipoxygenase (LOX) enzymes were recruited after pollen germination. Drug inhibition of LIP and LOX enzymes hampered both pollen germination and pollen tube growth, leading to a characteristic accumulation pattern of OBs at the germinative aperture. We propase that two independent pathways involving LIP and LOX/PX enzymes, respectively, are responsible for early mobilization of neutrallipids in the pollen tube, while PLAs may promete the access of these enzymes to the OB matrix. Moreover, pollen performance in vitro was not affected under sugar-deprivation conditions but OBassociated enzyme activities were enhanced and OB mobilization was sped up. These data suggest that OBs are sufficient to promote the autonomous growth of the olive pollen tube at the onset of germination, while sugar availability may modulate the activity of these degrading enzymes.