Interactions between a mechanosensitive channel and cell wall integrity signaling influence pollen germination in Arabidopsis thaliana

Cells employ multiple systems to maintain cellular integrity, including mechanosensitive ion channels and the cell wall integrity (CWI) pathway. Here, we use pollen as a model system to ask how these different mechanisms are interconnected at the cellular level. MscS-Like 8 (MSL8) is a mechanosensitive channel required to protect Arabidopsis thaliana pollen from osmotic challenges during in vitro rehydration, germination, and tube growth. New CRISPR/Cas9 and artificial miRNA-generated msl8 alleles produced unexpected pollen phenotypes, including the ability to germinate a tube after bursting, dramatic defects in cell wall structure, and disorganized callose deposition at the germination site. We document complex genetic interactions between MSL8 and two previously established components of the CWI pathway, MARIS and ANXUR1/2. Overexpression of MARIS(R240C)-FP suppressed the bursting, germination, and callose deposition phenotypes of msl8 mutant pollen. Null msl8 alleles suppressed the internalized callose structures observed in MARIS(R240C)-FP lines. Similarly, MSL8-YFP overexpression suppressed bursting in the anxur1/2 mutant background, while anxur1/2 alleles reduced the strong rings of callose around ungerminated pollen grains in MSL8-YFP overexpressors. These data show that mechanosensitive ion channels modulate callose deposition in pollen and provide evidence that cell wall and membrane surveillance systems coordinate in a complex manner to maintain cell integrity. A mechanosensitive channel alters normal callose deposition and interacts with the cell wall integrity pathway, implicating crosstalk between plasma membrane- and cell wall-based mechanisms in pollen germination.

Automated summary

Cells have multiple systems, including ion channels and the cell wall integrity pathway, to maintain cellular integrity. Through studying pollen, it has been discovered that mechanosensitive ion channels modulate callose deposition and interact with the cell wall integrity pathway to maintain cell integrity.