2n pollen production by extreme low temperature-induced failure of male post-meiotic cytokinesis in Populus

Polyploidization by forming diploid gametes is an important force driving diversification and speciation in plant evolution. The prevalence of polyploids in adverse climates led us to underline that abiotic stress conditions can result in unreduced gametes. In the present study, we revealed that short periods of extreme low temperature (ELT) caused defects in male post-meiotic cytokinesis by interfering with the formation of the radial microtubule array, resulting in meiotic restitution and 2n pollen production in Populus. A protocol for inducing 2n pollen by ELT was established. The dominant meiotic stage (F = 19.804, P < 0.001), low temperature (F = 30.656, P < 0.001), and duration (F = 5.554, P = 0.005) significantly affected the frequency of induced 2n pollen. The highest frequency of induced 2n pollen (31.11%) was observed when the dominant meiotic stage of the pollen mother cells was metaphase II and was stressed by -13℃ for 5 h. Twenty-six triploids were produced by crossing induced 2n pollen. Therefore, we developed a reliable and efficient method for triploid breeding of plants. Our findings provide new insight into the mechanisms of ELT-induced 2n pollen formation in a woody plant and verify that sensitivity to environmental stress has evolutionary importance in terms of polyploidization.