Full‐length EFOP3 and EFOP4 proteins are essential for pollen intine development in Arabidopsis thaliana.

SUMMARY: Pollen development is critical to plant reproduction, but the underlying regulatory molecular mechanisms have not been fully elucidated. The Arabidopsis (Arabidopsis thaliana) EFR3 OF PLANT 3 (EFOP3) and EFR3 OF PLANT 4 (EFOP4) genes encode members of the Armadillo (ARM) repeat superfamily that play key roles in pollen development. Herein, we demonstrate that EFOP3 and EFOP4 are co‐expressed in pollen at anther stages 10–12, but loss‐of‐function of both EFOP3 and EFOP4 leads to male gametophyte sterility, irregular intine, and shriveled pollen grains at anther stage 12. We further established that full‐length EFOP3 and EFOP4 specifically localize to the plasma membrane, and the integrity of these proteins is essential for pollen development. We observed uneven intine, less organized cellulose and reduced pectin content in mutant pollen compared with the wild‐type. These, together with the misexpression of several genes related to cell wall metabolism in efop3−/− efop4+/− mutants, suggest that EFOP3 and EFOP4 may indirectly regulate the expression of these genes to affect intine formation, thus controlling Arabidopsis pollen fertility in a functionally redundant manner. Moreover, transcriptome analysis showed that the absence of EFOP3 and EFOP4 function affects multiple pollen development pathways. These results enhance our understanding of EFOPs proteins and their role in pollen development. Significance Statement: We show that the integrity of EFOP3 and EFOP4 proteins is essential for their specific association with the plasma membrane of pollen, and is required for pollen intine development in Arabidopsis (Arabidopsis thaliana). EFOP3 and EFOP4 may indirectly regulate the expression of cell wall metabolism‐related genes to affect intine formation, thus controlling Arabidopsis pollen fertility in a functionally redundant manner. [ABSTRACT FROM AUTHOR]

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