436 / 2019-01-29 11:12:04

Mutation of Arabidopsis SAURs impairs the efficient translation of transcripts essential for pollen tube growth

SAUR, ribosome assembly, actin cytoskeleton, pectin wall

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Successful pollen tube elongation is critical for double fertilization, but the biological functions of pollen tube genes and the regulatory machinery underlying this crucial process are largely unknown. A previous translatomic study revealed two Arabidopsis SAUR genes, SAUR62 and SAUR75, whose expression is upregulated by pollination. Here, we found that both SAUR62 and SAUR75 mainly localized to pollen tube nuclei. The siliques of saur62/-, saur75/-, and the SAUR62/75 RNAi line had many aborted seeds. These lines had normal pollen viability but defective in vitro and in vivo pollen tube growth, with branching phenotypes. Immunoprecipitation with transgenic SAUR62/75-GFP flowers revealed ribosomal protein RPL12s as potential interacting partners, and their individual interactions were further confirmed by Y2H and BiFC assays. Polysome profiling showed reduced 80S ribosome abundance in saur62, saur75, rpl12c and SAUR62/75 RNAi flowers, suggesting that SAUR62/75 play roles in ribosome assembly. To clarify their roles in translation, we analyzed total proteins from RNAi vs. WT flowers by iTRAQ, revealing significantly reduced expression of factors participating in pollen tube wall biogenesis and F-actin dynamics, which are critical for the elastic properties of tube elongation. Thus, the biological roles of SAUR62/75 and their RPL12 partners are critical in ribosomal assembly for efficient pollen tube elongation and subsequent fertilization.