Abstract
During microsporogenesis, the microsporocyte (or microspore) plasma membrane plays multiple roles in pollen wall development, including callose secretion, primexine deposition, and exine pattern determination. However, plasma membrane proteins that participate in these processes are still not well known. Here, we report that a new gene, RUPTURED POLLEN GRAIN1 (RPG1), encodes a plasma membrane protein and is required for exine pattern formation of microspores in Arabidopsis (Arabidopsis thaliana). The rpg1 mutant exhibits severely reduced male fertility with an otherwise normal phenotype, which is largely due to the postmeiotic abortion of microspores. Scanning electron microscopy examination showed that exine pattern formation in the mutant is impaired, as sporopollenin is randomly deposited on the pollen surface. Transmission electron microscopy examination further revealed that the primexine formation of mutant microspores is aberrant at the tetrad stage, which leads to defective sporopollenin deposition on microspores and the locule wall. In addition, microspore rupture and cytoplasmic leakage were evident in the rpg1 mutant, which indicates impaired cell integrity of the mutant microspores. RPG1 encodes an MtN3/saliva family protein that is integral to the plasma membrane. In situ hybridization analysis revealed that RPG1 is strongly expressed in microsporocyte (or microspores) and tapetum during male meiosis. The possible role of RPG1 in microsporogenesis is discussed.
Highlights
IntroductionThe microsporocyte (or microspore) plasma membrane plays multiple roles in pollen wall development, including callose secretion, primexine deposition, and exine pattern determination
During microsporogenesis, the microsporocyte plasma membrane plays multiple roles in pollen wall development, including callose secretion, primexine deposition, and exine pattern determination
RUPTURED POLLEN GRAIN1 (RPG1) exhibits its strongest expression in microsporocytes and tapetum during microsporogenesis, which confirms the important role of this gene in the early determination of microspore formation and exine pattern formation
Summary
The microsporocyte (or microspore) plasma membrane plays multiple roles in pollen wall development, including callose secretion, primexine deposition, and exine pattern determination. We report that a new gene, RUPTURED POLLEN GRAIN1 (RPG1), encodes a plasma membrane protein and is required for exine pattern formation of microspores in Arabidopsis (Arabidopsis thaliana). DEX1 encodes a predicted membrane-associated protein that contains several potential calcium-binding domains (PaxsonSowders et al, 2001) In another conditional sterile mutant, faceless pollen ( flp1/cer3-7), the inviable pollen has a smooth surface due to the coverage of the exine baculae of the pollen grain by an excess of tryphine (Ariizumi et al, 2003). The FLP1 (recently designated CER3/WAX2/YRE/FLP1) gene encodes a lipid transfer protein that is important for wax biosynthesis (Ariizumi et al, 2003; Chen et al, 2003; Kurata et al, 2003; Rowland et al, 2007)
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