Biogeographic cline is associated with the global plant telomere length variation.

Telomeres have the crucial role of protecting chromosome ends and its length varies significantly between organisms. What evolutionary factor shapes this natural variation has been a long standing question, with answers providing insights into chromosome function and evolution. In animals life-history variation relating to senescence or tumorigenesis explains telomere length variation. For plants, however, we lack knowledge of what factor is driving their length variation in nature. Is life-history differences also driving telomere length variation among plant species? We answer this question by analyzing the telomeres of 257 plant species spanning the major orders of the green plant kingdom. Telomere lengths were estimated for species that vary significantly in their life-history, geographical distribution, and trait characters. Results showed telomere length increased with the evolution of terrestrialization, where Chlorophytes had the shortest telomeres and Spermatophytes had the longest telomeres. Surprisingly, plants with different life-histories had minimal telomere length differences, but biogeographic clines had significant effect on telomere length variation. Plant telomere length increases closer to the equator, while telomere length decreases at higher altitude. Domestication was previously proposed to lengthen telomeres, but we found no consistent domestication effect on telomere lengths comparing crops and their wild progenitors. From our results we conclude plant telomere length contrasts with animal telomeres, in that life-history has minimal effect on length variation. Instead we propose the ecological adaptation hypothesis, where telomere length in plants is determined by selection from abiotic conditions, and suggest temperature is a major factor shaping telomere length in plants.