Mechanosensitive ion channel MSL8 is required for oscillatory growth and cell wall dynamics in Arabidopsis pollen tubes.

Abstract

The male gametophyte in flowering plants, pollen, both performs the critical role of fertilization and represents a unique and accessible system for interrogating plant cell mechanics. A key component in this robust mechanical system is MscS-Like 8 (MSL8), a mechanosensitive ion channel. We previously proposed that MSL8 serves as an "osmotic safety valve", regulating pressure in the germinating pollen tube by releasing anions in response to plasma membrane tension. However, we subsequently identified defects in the cell walls of msl8 mutant pollen that suggested a role independent of osmoregulation. Here, we show that pollen tubes lacking MSL8 channel function by genetic knockout or channel-blocking point mutation lose major growth pauses, have altered pectin esterification patterns, and are sensitive to pectin crosslinking. Together, these data suggest a mechanism whereby anion efflux through mechanosensitive channels regulates cell wall composition and growth dynamics.