Proteomic Analyses of Maize Cross Incompatibility Gene Ga1-S

Ga1-S is a gametophytic mutant involved in maize cross incompatibility. The presence of the dominant allele Ga1-S in silks prevents fertilization by pollen carrying the recessive allele ga1. The physiological basis of cross incompatibility is poorly understood. The proteomic profiling of Ga1-S silks pollinated with Ga1-S and ga1 pollen was investigated for isolating genes involved in cross incompatibility in maize. Two near isogenic lines on Ga1-S locus, W22 (GG) and w22 (gg), were used to make reciprocally crosses of GG × GG, gg × GG, and GG × gg. The behaviours of pollen tube growth in the 3 crosses were compared under a fluorescence microscopy, and the proteomic profiles of total silk proteins in W22 (GG) were compared 10 h after pollination by GG or gg pollen. The total silk proteins of GG × GG and GG × gg crosses were extracted using TCA/Acetone method, separated through electrophoresis in 2-dimensional gels, and analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS). The results indicated that gg pollen grains germinated well and the pollen tubes were able to enter the GG silk transmitting tract. However, no gg pollen tube reached GG ovule area, which resulted in incompatibility. In the silk proteomes of GG × GG and GG × gg, 25 differentially expressed proteins were identified, including 15 specifically expressed in GG × GG, and 10 specifically expressed in GG × gg. Among these proteins, 12 were annotated in various databases after MALDI-TOF-MS and MASCOT analyses. Proteins 11, 12, 14, 18, 22, and 24 presumably play important roles in the cross-incompatibility of maize.