Arabidopsis aspartic proteases A36 and A39 play roles in plant reproduction

Aspartic proteases (Aps, EC3.4.23) are one of the 4 major mechanistic classes of proteolytic enzymes with the conserved motifs Asp-Thr/Ser-Gly (DT/SG) at the active site and are activated at acidic pH. In Arabidopsis, 69 genes were identified as coding putative aspartic proteinases. However, little is known about most of these enzymes. Recently, we characterized 2 novel Arabidopsis Aps genes, A36 and A39, which encode 2 putative GPI-anchored pollen-high-expressed Aps. a36 a39 mutants display significant abortion. The pollen grains underwent apoptosis-like programmed cell death and the degeneration of female gametes was also appeared in the a36 a39 mutant. Besides, the pollen tube of a36 a39 has compromised micropylar guidance. A36 and A39 were membrane-anchored protein and co-localized with a reported GPI-anchored protein COBRA-LIKE 10 (COBL10). In apical region of a36 a39 pollen tubes cell wall, the abundance of highly methlyestered homogalacturonans and xyloglucans were significantly increased. These results indicated that A36 and A39 are vital factors involved in gametogenesis and pollen guidance in Arabidopsis.