Pectin methylesterase activities in reproductive tissues of maize plants with different haplotypes of the Ga1 and Ga2 cross incompatibility systems

Authors: BAPAT, AMRUTA - Iowa State University; Scott, Marvin

Submitted to: Plant Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2024
Publication Date: 5/3/2024
Citation: Bapat, A.R., Scott, M.P. 2024. Pectin methylesterase activities in reproductive tissues of maize plants with different haplotypes of the Ga1 and Ga2 cross incompatibility systems. Plant Reproduction. https://doi.org/10.1007/s00497-024-00502-0.
DOI: https://doi.org/10.1007/s00497-024-00502-0

Interpretive Summary: Ga1 and Ga2 are systems of genes in corn that control the effectiveness of fertilization in crosses between plants. The details of how the Ga1 and Ga2 genes function at a molecular level are not fully understood. The genes are similar to genes that encode enzymes known to be important for fertilization, but we don't know if the presence of Ga1 and Ga2 genes alter the activity of the enzymes required for fertilization. In order to answer this question, we measured enzyme activity in plants with and without the Ga1 and Ga2 genes. Enzyme activity was related to the presence of the Ga1 and Ga2 genes. Investigation of mutations in the genes of each system reveals that they may not contribute directly to enzyme activity, but instead play a role in regulating enzyme activity. These observations will allow scientists to better understand the process of fertilization and will be applied by researchers to benefit plant breeding and crop production.

Technical Abstract: In maize cross incompatibility systems, the pollination outcome depends on the haplotypes of the interacting male gametophyte (pollen) and female sporophyte (silk) at several loci. Functional alleles of the cross-incompatibility loci Ga1 and Ga2, both encode two pectin methylesterases (PMEs), one that is expressed in silk and the other in pollen. We examined total PME activity in reproductive tissues containing different haplotypes of the Ga1 and Ga2 systems. We identified a relationship between the presence of the silk-expressed PME in and total PME activity in silks in both the Ga1 and Ga2 systems. In pollen, the presence of the pollen-expressed PME was related to total PME activity in Ga1. In pollinated silks, there was a relationship between total PME activity and the presence of the pollen-expressed PME. Total PME activity was related to the pollination outcome in crosses containing the functional silk-expressed PME, but crosses lacking this PME that had similar total PME activity levels and resulted in compatible crosses, suggesting that a given level of PME activity can lead to different pollination outcomes. In Ga2 tissues, the pattern of PME activities was consistent with that of the Ga1 system. We re-examined previously reported active site amino acid substitutions in PMEs encoded by cross incompatibility loci. We observed that different active site substitutions are present in the pollen and silk expressed PMEs and these differences are conserved across all three molecularly characterized cross incompatibility systems (Ga1, Ga2 and Tcb-1). This work for establishes a relationship between total PME activity and presence of haplotypes of a cross incompatibility locus in pollinated silks.