Specific pollen extensins LRX are required for maintaining cell wall integrity during pollen tube growth in Arabidopsis thaliana

Abstract

Polarized growth of pollen tubes is an oscillatory mechanism that involves a tight coordination of Ca2+ ions and Reactive Oxygen Species(ROS) with high trafficking of vesicles to the tip where a constant remodeling of the cell wall occurs. During this process, it is crucial theregulatory and structural roleof thecell wall and the presenceof glycoproteins and homogalacturonans which are involved in cell wall crosslinking contributing to maintain its proper assembly. Here, we studied thefunction of 4 pollen specificLRX8-11 (Leucine-rich Repeat Extensin-like) proteins which belong to the HRGP (Hydroxyproline-rich glycoprotein) family in Arabidopsis thaliana. These chimeric proteins have an N-terminalLRR (Leucine-rich repeat) domain and a C-terminalextensin (EXT)-like domain with Ser-Prorepetitions possibly glycosylated.The analysisofsimple, double and one triple LRX knock-out mutants revealed an important reduction in pollen germination rates and a skewed segregation ratio due to defects in pollen transmission. We also found severe abnormalities in pollen tube morphology with the concomitant anomalous deposition of pectin and callose at the cell wall. All together these results suggest that pollen LRX(8- 11) are necessary to maintain cell wall integrity and prevent tip bursting during pollen germination and polarized growth of pollen tubes.