The Role of INAPERTURATE POLLEN1 as a Pollen Aperture Factor Is Conserved in the Basal Eudicot Eschscholzia californica (Papaveraceae)

Abstract

Pollen grains show an enormous variety of aperture systems. What genes are involved in the aperture formation pathway and how conserved this pathway is in angiosperms remains largely unknown. INAPERTURATE POLLEN1 (INP1) encodes a protein of unknown function, essential for aperture formation in Arabidopsis, rice and maize. Yet, because INP1 sequences are quite divergent, it is unclear if their function is conserved across angiosperms. Here, we conducted a functional study of the INP1 ortholog from the basal eudicot Eschscholzia californica (EcINP1) using expression analyses, virus-induced gene silencing, pollen germination assay, and transcriptomics. We found that EcINP1 expression peaks at the tetrad stage of pollen development, consistent with its role in aperture formation, which occurs at that stage, and showed, via gene silencing, that the role of INP1 as an important aperture factor extends to basal eudicots. Using germination assays, we demonstrated that, in Eschscholzia, apertures are dispensable for pollen germination. Our comparative transcriptome analysis of wild-type and silenced plants identified over 900 differentially expressed genes, many of them potential candidates for the aperture pathway. Our study substantiates the importance of INP1 homologs for aperture formation across angiosperms and opens up new avenues for functional studies of other aperture candidate genes.

Microstructure of Croatian Wild Grapevine (Vitis vinifera subsp. sylvestris Gmel Hegi) Pollen Grains Revealed by Scanning Electron Microscopy

“…In Arabidopsis , a shorter aperture length proved to be related to lower transcript levels of the INP1 gene. Although INP1 is essential for aperture development, it is not the main factor defining aperture number, positions and morphology [ 24 ].…”

“…Male sterility in female individuals is associated with a lack of pollen apertures. Regions at the pollen surface with little or no exine deposition, and one of the most characteristic and well-defined structures of the pollen surface [ 24 ], are crucial in reproduction as a site for initial pollen tube growth [ 25 ]. Two predominant morphotypes are observed based on the apertures in the grapevine.…”

California poppy (Eschscholzia californica), the Papaveraceae golden girl model organism for evodevo and specialized metabolism

“…California poppy also served to show that the function of INAPERTURATE POLLEN (INP1), a gene required for aperture formation in pollen grains to allow pollen grain germination, is conserved throughout monocots and dicots, even though sequence divergence of orthologs is comparatively high (Mazuecos-Aguilera et al, 2021).…”

A Review of the Developmental Processes and Selective Pressures Shaping Aperture Pattern in Angiosperms

“…In Arabidopsis thaliana, rice, and maize, the loss of the INP1 protein causes a complete aperture loss, suggesting a role of INP1 as an aperture factor [37][38][39]. The role of INP1 is conserved in Eschscholzia californica [40]. INP2 has been identified as a partner of INP1 [41], and inp2 mutant displays inaperturate pollen grain.…”