Abstract
BackgroundIn Arabidopsis, the tapetum and microsporocytes are critical for pollen formation. Previous studies have shown that ARF17 is expressed in microsporocytes and tetrads and directly regulates tetrad wall synthesis for pollen formation. ARF17 is the direct target of miR160, and promoterARF17::5mARF17 (5mARF17/WT) transgenic plants, which have five silent mutations within the miR160-complementary domain, are sterile.ResultsHere, we found that ARF17 is also expressed in the tapetum, which was defective in arf17 mutants. Compared with arf17 mutants, 5mARF17/WT plants had abnormal tapetal cells and tetrads but were less vacuolated in the tapetum. Immunocytochemical assays showed that the ARF17 protein over-accumulated in tapetum, microsporocytes and tetrads of 5mARF17/WT plants at early anther stages, but its expression pattern was not affected during anther development. 5mARF17 driven by its native promoter did not rescue the arf17 male-sterile phenotype. The expression of 5mARF17 driven by the tapetum-specific promoter A9 led to a defective tapetum and male sterility in transgenic plants. These results suggest that the overexpression of ARF17 in the tapetum and microsporocytes of 5mARF17/WT plants leads to male sterility. Microarray data revealed that an abundance of genes involved in transcription and translation are ectopically expressed in 5mARF17/WT plants.ConclusionsOur work shows that ARF17 plays an essential role in anther development and pollen formation, and ARF17 expression under miR160 regulation is critical for its function during anther development.
Highlights
In Arabidopsis, the tapetum and microsporocytes are critical for pollen formation
ARF17 is essential for tapetum development Previous investigations have shown that ARF17 directly regulates the expression of CALLOSE SYNTHASE 5 (CALS5) for tetrad wall formation
We found that tapetum development was defective in arf17 mutants and was abnormally vacuolated during development from stage 7 to stage 9 (Fig. 1a, b)
Summary
In Arabidopsis, the tapetum and microsporocytes are critical for pollen formation. Previous studies have shown that ARF17 is expressed in microsporocytes and tetrads and directly regulates tetrad wall synthesis for pollen formation. ARF17 is the direct target of miR160, and promoterARF17::5mARF17 (5mARF17/WT) transgenic plants, which have five silent mutations within the miR160-complementary domain, are sterile. Haploid microspores further develop into pollen grains within the locules. Each locule contains four somatic layers that surround microsporocytes/microspores/pollen [1]. The pollen wall is typically composed of an exine and intine. The innermost layer of locule sporophytic tissue, the tapetum, is in direct contact with the microspores to provide necessary nutrition and pollen wall materials for pollen grain maturation [2, 3]. The deposition pattern of the exine is determined by callose formation during the tetrad stage [4, 5]
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