Functional study of leucine-rich repeat extensins (LRXs) and prolyl-4-hydroxylases (P4Hs) during pollen tube growth

SEDE, A.R.; MECCHIA MA; BORASSI, C.; ESTEVEZ J.M. ; WENGIER D.; MUSCHIETTI, J.P.

CABA

Simposio; 3rd Argentinian Symposium on Glycobiology; 2019

Polarized growth of pollen tubes implicates the constant remodeling of the cell wall at the apical region. The presence of polysaccharides and structural proteins such as Hydroxyproline-rich glycoproteins (HRGPs) involved in the crosslinking at the cell wall is crucial to maintain cell wall integrity. One of the members of HRGP family are the leucine-rich repeat extensins (LRXs) which contain a leucine-rich repeat N-terminal domain and a C-terminal extensin domain with several Ser(Pro)3-5 repetitions plausible to be glycosylated. In this study, we demonstrated that pollen specific LRXs, LRX8-LRX11, are necessary to maintain the correct assembly of the cell wall during polarized growth of pollen tubes. We observed that the lack of LRX8-LRX11 affects pollen germination, the cell wall integrity of pollen tubes and alters mendelian inheritance. Moreover, loss of function triple mutant lrx9 lrx10 lrx11 pollen tubes displayed an over accumulation of pectin and callose at the cell wall. Since proline hydroxylation of extensins is necessary to define future O-glycosylation sites, we aimed to study the function of two pollen specific enzymes from the prolyl-4-hydroxylase (P4H) family, P4H4 and P4H6. Our results showed a decrease in pollen germination of loss of function p4h4 and p4h6 mutants as well as by blocking P4Hs activity with specific P4H inhibitors. Finally, we observed that P4H4 localized in the endoplasmic reticulum/Golgi apparatus of growing pollen tubes. Additional analysis will be required to study the relevance of the hydroxylation over pollen structural HRGPs proteins, specifically the functional involvement of P4H4 and P4H6 in the hydroxylation of pollen LRXs.