Abstract
The trans-Golgi network (TGN) plays a central role in cellular secretion and has been implicated in sorting cargo destined for the plasma membrane. Previously, the Arabidopsis (Arabidopsis thaliana) echidna (ech) mutant was shown to exhibit a dwarf phenotype due to impaired cell expansion. However, ech also has a previously uncharacterized phenotype of reduced male fertility. This semisterility is due to decreased anther size and reduced amounts of pollen but also to decreased pollen viability, impaired anther opening, and pollen tube growth. An ECH translational fusion (ECHPro:ECH-yellow fluorescent protein) revealed developmentally regulated tissue-specific expression, with expression in the tapetum during early anther development and microspore release and subsequent expression in the pollen, pollen tube, and stylar tissues. Pollen viability and production, along with germination and pollen tube growth, were all impaired. The ech anther endothecium secondary wall thickening also appeared reduced and disorganized, resulting in incomplete anther opening. This did not appear to be due to anther secondary thickening regulatory genes but perhaps to altered secretion of wall materials through the TGN as a consequence of the absence of the ECH protein. ECH expression is critical for a variety of aspects of male reproduction, including the production of functional pollen grains, their effective release, germination, and tube formation. These stages of pollen development are fundamentally influenced by TGN trafficking of hormones and wall components. Overall, this suggests that the fertility defect is multifaceted, with the TGN trafficking playing a significant role in the process of both pollen formation and subsequent fertilization.
Highlights
The trans-Golgi network (TGN) plays a central role in cellular secretion and has been implicated in sorting cargo destined for the plasma membrane
The extent of genomic involvement in pollen development is illustrated by the high frequency of mutations that result in a failure of male fertility; these can be a consequence of the failure of pollen development or pollen release, dehiscence
We have shown that ECH expression is critical for a variety of aspects of male reproduction, which include the production of functional pollen grains, their effective release, and subsequent germination and pollen tube formation
Summary
The trans-Golgi network (TGN) plays a central role in cellular secretion and has been implicated in sorting cargo destined for the plasma membrane. ECH expression is critical for a variety of aspects of male reproduction, including the production of functional pollen grains, their effective release, germination, and tube formation. These stages of pollen development are fundamentally influenced by TGN trafficking of hormones and wall components. The structure of the maternal anther cell layers has been shown to be critical for the production and release of functional pollen, as demonstrated in a number of male-sterile mutants, which have defects in cell division and early stages of differentiation of the tapetum and sporogenous cells. Mutants of the Leu-rich repeat receptor kinase EXTRA SPOROGENOUS CELLS (EXS)/EXCESS MICROSPOROCYTES1 (Canales et al, 2002; Zhao et al, 2002) and its ligand TAPETAL DETERMINANT1 (Jia et al, 2008) result in sterility due to the formation of additional male sporocytes and a lack of tapetal cells
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