SYP72 interacts with the mechanosensitive channel MSL8 to protect pollen from hypoosmotic shock during hydration

Xuemei Zhou,Mengdi Li,Haiming Li,Yingying Guo,Meng-Xiang Sun,Yifan Zheng,Ling Wang,Peng Zhao

doi:10.1038/s41467-021-27757-9

Abstract

In flowering plants, hydration of desiccated pollen grains on stigma is a prerequisite for pollen germination, during which pollen increase markedly in volume through water uptake, requiring them to survive hypoosmotic shock to maintain cellular integrity. However, the mechanisms behind the adaptation of pollen to this hypoosmotic challenge are largely unknown. Here, we identify the Qc-SNARE protein SYP72, which is specifically expressed in male gametophytes, as a critical regulator of pollen survival upon hypoosmotic shock during hydration. SYP72 interacts with the MSCS-LIKE 8 (MSL8) and is required for its localization to the plasma membrane. Intraspecies and interspecies genetic complementation experiments reveal that SYP72 paralogs and orthologs from green algae to angiosperms display conserved molecular functions and rescue the defects of Arabidopsis syp72 mutant pollen facing hypoosmotic shock following hydration. Our findings demonstrate a critical role for SYP72 in pollen resistance to hypoosmotic shock through the MSL8 cascade during pollen hydration.

Highlights

In flowering plants, hydration of desiccated pollen grains on stigma is a prerequisite for pollen germination, during which pollen increase markedly in volume through water uptake, requiring them to survive hypoosmotic shock to maintain cellular integrity
We focused on SYNTAXIN OF PLANTS 72 (SYP72), a member of the plant-specific SYP7 gene family within the Qc-SNARE clade that is abundantly expressed in mature pollen and the pollen tube and had not previously been functionally characterized
Consistent with transcriptome deep sequencing (RNA-seq) data, SYP72 is expressed in the male but not the female gametophyte, as evidenced by green fluorescence in pSYP72:H2B-GFP transgenic plants expressing a nuclear-targeted green fluorescent protein (GFP) driven by the SYP72 promoter, and pSYP72:GFPSYP72 transgenic plants expressing a translational fusion of the GFP and SYP72 driven by the SYP72 promoter (Fig. 1a–d and Supplementary Fig. 2a, b)

Summary

Results

Both RNA-seq data and reporter analysis with GFP-SYP constructs driven by their respective promoters revealed that only SYP72 is expressed in mature pollen, whereas SYP71 and SYP73 expression was barely detectable in mature pollen (Fig. 1a, b and Supplementary Fig. 2), suggesting that each member of the SYP7 subfamily plays tissuespecific roles in plant development, with little redundancy These interesting characteristics of SYP7 subfamily SNAREs prompted us to investigate whether the three SYP7 members might have a conserved molecular function in promoting MSL8 localization to the plasma membrane, even though they have different expression patterns. The counterparts of SYP72 appeared specific to the Brassicaceae, as they were present in GFP-SYP72 cw mCherry-NPSN12 cw

Channel

Discussion

Methods