Involved in the deposition of apical pectin cap and cellulose microfibrils in pollen tubes (PubMed:23384085). Not essential for pollen development, hydration or germination, but required for pollen tubes growth in the female transmitting tract of pistil and toward micropyles, via the perception of ovule guidance cues (PubMed:23384085, PubMed:24963069, PubMed:27872247). Localization to the plasma membrane is dependent of the GPI-anchor at Ser-646 (PubMed:24963069, PubMed:23384085). Localized at the apical plasma membrane of pollen tubes (PubMed:24963069, PubMed:23384085). Colocalizes with A36 and A39 at the plasma membrane and in the cytoplasm in the growing pollen tubes (PubMed:27872247). In the cytoplasm, observed in motile punctate vesicles (PubMed:23384085). Expressed in roots, stems, leaves, flowers and siliques (PubMed:12376623). Specific expression in the pollen tube (PubMed:23384085). The GPI-anchor attachment at Ser-646 requires APTG1. Gametophytic male sterility due to reduced pollen tube growth and compromised directional ovular guidance cues sensing in the female transmitting tract, thus leading to an abnormal pollen tubes guidance growth toward micropyles (PubMed:24963069, PubMed:27872247, PubMed:23384085). Normal pollen development, hydration and germination (PubMed:23384085). Disrupted apical pectin cap and cellulose microfibrils deposition in pollen tubes resulting in an abnormal cell wall organization (PubMed:23384085). Belongs to the COBRA family.