Two Membrane-Anchored Aspartic Proteases Contribute to Pollen and Ovule Development

Abstract

Aspartic proteases are a class of proteolytic enzymes with conserved aspartate residues, which are implicated in protein processing, maturation, and degradation. Compared with yeast and animals, plants possess a larger aspartic protease family. However, little is known about most of these enzymes. Here, we characterized two Arabidopsis (Arabidopsis thaliana) putative glycosylphosphatidylinositol (GPI)-anchored aspartic protease genes, A36 and A39, which are highly expressed in pollen and pollen tubes. a36 and a36 a39 mutants display significantly reduced pollen activity. Transmission electron microscopy and terminaldeoxynucleotidyl transferase-mediated nick end labeling assays further revealed that the unviable pollen in a36 a39 may undergo unanticipated apoptosis-like programmed cell death. The degeneration of female gametes also occurred in a36 a39. Aniline Blue staining, scanning electron microscopy, and semi in vitro guidance assays indicated that the micropylar guidance of pollen tubes is significantly compromised in a36 a39. A36 and A39 that were fused with green fluorescent protein are localized to the plasma membrane and display punctate cytosolic localization and colocalize with the GPI-anchored protein COBRA-LIKE10. Furthermore, in a36 a39, the abundance of highly methylesterified homogalacturonans and xyloglucans was increased significantly in the apical pollen tube wall. These results indicate that A36 and A39, two putative GPI-anchored aspartic proteases, play important roles in plant reproduction in Arabidopsis.

Plant proteases during developmental programmed cell death

“…Next to cysteine proteases, aspartic proteases have been implicated in PCD processes throughout plant development, including tapetum PCD (Gao et al, 2017a;Gao et al, 2017b;Ge et al, 2005). Two aspartic proteases in rice, OsAP25 and OsAP37, have been found to be under direct transcriptional control of ETERNAL TAPETUM1 (EAT1) (Niu et al, 2013).…”

The Temperature-Dependent Retention of Introns in GPI8 Transcripts Contributes to a Drooping and Fragile Shoot Phenotype in Rice

“…In several mutants, loss of function of GPI-AP severely affects pollen development, pollen germination efficiency, and pollen tube growth. Examples include classical AGPs [19], aspartic protease [20], ENODL11-15 proteins that contain an early-nodulin like/plastocyanin domain [21], and LORELEI [22]. Other functions of the GPI-APs include immune recognition, transmembrane signaling, embryogenesis, formation of stomata, and export of cuticular wax [23].…”

Processes Underlying a Reproductive Barrier in indica-japonica Rice Hybrids Revealed by Transcriptome Analysis

“…In Pichia pastoris and Saccharomyces cerevisiae, extracellular aspartic protease yapsins are required for the CWI maintenance (Krysan et al, 2005;Guan et al, 2012). Two plant aspartic proteases, A36 and A39, participate in cell wall remodeling in pollen tube (Gao et al, 2017). The study in Candida albicans shows that secreted aspartic proteinases use a set of cell wall proteins as substrates (Schild et al, 2011).…”