Meiotic Thermal Tolerance in Arabisopsis arenosa

How does adaptation to external abiotic environments affect meiosis, gamete development, and recombination? Meiosis is a tightly regulated process fundamental to all sexual reproducing organisms. Stabilizing selection upon proper chromosome pairing and crossing-over is strong because the mis-segregation of homologs can result in sterility and/or lethality. Meiotic processes are sensitive to the environment, particularly temperature, in which gametes develop. It is largely unknown whether the meiotic machinery of organisms native to different thermal environments is locally adapted to function at specific temperatures. We investigate this question by measuring pollen fertility and prophase I markers of meiotic progression – synaptonemal complex (SC) development- in populations of Arabidopsis arenosa from the hot/dry Pannonian Basin and cool/wet Carpathian Mountains of central Europe. We find that plants from these regions have significantly higher pollen fertility when grown at native versus non-native temperature conditions. The reduction in pollen fertility of plants from the Carpathians at high temperature is associated with the failure of SC establishment.  In order to identify candidate genes that may underlie this phenotypic variation, we measured genome-wide genetic differentiation between Pannonian and Carpathians populations. Of the 148 meiosis functioning proteins, only three exhibit significant differentiation between populations. Interestingly all three of them are structural, SC associated proteins. Patterns of genetic variation within populations are consistent with selection in the Pannonian lineage and may contribute to greater thermal tolerance in SC establishment and pollen viability.