Abstract
BackgroundThe pollen wall, which protects male gametophyte against various stresses and facilitates pollination, is essential for successful reproduction in flowering plants. The pollen wall consists of gametophyte-derived intine and sporophyte-derived exine. From outside to inside of exine are tectum, bacula, nexine I and nexine II layers. How these structural layers are formed has been under extensive studies, but the molecular mechanisms remain obscure.ResultsHere we identified two osabcg3 allelic mutants and demonstrated that OsABCG3 was required for pollen development in rice. OsABCG3 encodes a half-size ABCG transporter localized on the plasma membrane. It was mainly expressed in anther when exine started to form. Loss-function of OsABCG3 caused abnormal degradation of the tapetum. The mutant pollen lacked the nexine II and intine layers, and shriveled without cytoplasm. The expression of some genes required for pollen wall formation was examined in osabcg3 mutants. The mutation did not alter the expression of the regulatory genes and lipid metabolism genes, but altered the expression of lipid transport genes.ConclusionsBase on the genetic and cytological analyses, OsABCG3 was proposed to transport the tapetum-produced materials essential for pollen wall formation. This study provided a new perspective to the genetic regulation of pollen wall development.
Highlights
The pollen wall, which protects male gametophyte against various stresses and facilitates pollination, is essential for successful reproduction in flowering plants
The seed set rates of pollinated osabcg3–1 and osabcg3–2 were comparable to that of osnp1–1 (Chang et al 2016a), a male sterility mutant without any defects in female reproduction (Additional file 1: Figure S1), indicating that the female fertility of osabcg3–1 and osabcg3–2 was normal. These results demonstrated that pollen abortion was accountable for the sterility of osabcg3–1 and osabcg3–2
In osabcg15 and osabcg26 mutants, the expression of TAPETUM DEGENERATION RETARDATION (TDR), WAX-DEFICIENT ANTHER 1 (WDA1), CYP704B2, OsC4 and OsC6 was all reduced, but the PERSISTANT TAPETAL CELL 1 (PTC1) transcript was increased (Niu et al 2013a; Qin et al 2013; Zhu et al 2013; Wu et al 2014; Zhao et al 2015; Chang et al 2016b). These results suggested that OsABCG3 regulates lipid metabolisms and transport during anther development in a way that different from OsABCG15 and OsABCG26
Summary
The pollen wall, which protects male gametophyte against various stresses and facilitates pollination, is essential for successful reproduction in flowering plants. From outside to inside of exine are tectum, bacula, nexine I and nexine II layers How these structural layers are formed has been under extensive studies, but the molecular mechanisms remain obscure. Anther is a male reproductive organ with a wall structure enclosing a locule where microspores develop (Zhang et al 2011). The anther wall consists of four layers of cells, from outside to inside, the epidermis, endothesium, middle layer and tapetum (Zhang et al 2011). The pollen wall is important for pollen function as it protects male gametophytes from various environmental stresses and facilitates pollination (Piffanelli et al 1998; Scott et al 2004)
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