Mechanical properties of the stigmatic cell wall mediate pollen tube path in Arabidopsis

Successful fertilization in angiosperms depends on the proper trajectory of pollen tubes through the pistil tissues to reach the ovules. Pollen tubes first grow within the cell wall of the papilla cells, applying pressure to the cell. Mechanical forces are known to play a major role in plant cell shape by controlling the orientation of cortical microtubules (CMTs), which in turn mediate deposition of cellulose microfibrils (CMFs). Here, by combining cell imaging and genetic approaches, we show that isotropic reorientation of CMTs and CMFs in aged and katanin1-5 (ktn1-5) papilla cells is accompanied by a tendency of pollen tubes to coil around the papillae. Furthermore, we uncover that aged and ktn1-5 papilla cells have a softer cell wall and provide less resistance to pollen tube growth. Our results reveal an unexpected role for KTN1 in pollen tube guidance by ensuring mechanical anisotropy of the papilla cell wall.