An ARID Domain-Containing Protein within Nuclear Bodies Is Required for Sperm Cell Formation in Arabidopsis thaliana

Abstract

In plants, each male meiotic product undergoes mitosis, and then one of the resulting cells divides again, yielding a three-celled pollen grain comprised of a vegetative cell and two sperm cells. Several genes have been found to act in this process, and DUO1 (DUO POLLEN 1), a transcription factor, plays a key role in sperm cell formation by activating expression of several germline genes. But how DUO1 itself is activated and how sperm cell formation is initiated remain unknown. To expand our understanding of sperm cell formation, we characterized an ARID (AT-Rich Interacting Domain)-containing protein, ARID1, that is specifically required for sperm cell formation in Arabidopsis. ARID1 localizes within nuclear bodies that are transiently present in the generative cell from which sperm cells arise, coincident with the timing of DUO1 activation. An arid1 mutant and antisense arid1 plants had an increased incidence of pollen with only a single sperm-like cell and exhibited reduced fertility as well as reduced expression of DUO1. In vitro and in vivo evidence showed that ARID1 binds to the DUO1 promoter. Lastly, we found that ARID1 physically associates with histone deacetylase 8 and that histone acetylation, which in wild type is evident only in sperm, expanded to the vegetative cell nucleus in the arid1 mutant. This study identifies a novel component required for sperm cell formation in plants and uncovers a direct positive regulatory role of ARID1 on DUO1 through association with histone acetylation.

Zygotic Genome Activation Occurs Shortly after Fertilization in Maize

“…Members of this class have been implicated in sperm cell development in plants and mammals. In Arabidopsis, ARID1 is necessary for the appropriate expression of DUO1, a major TF required for sperm cell formation (Zheng et al, 2014). In mice, the loss of ARID4A combined with ARID4B haploinsufficiency leads to spermatogenic arrest (Wu et al, 2013).…”

A Conserved cis-Regulatory Module Determines Germline Fate through Activation of the Transcription Factor DUO1 Promoter

“…1A). These enhancer regions could function by promoting the formation of permissive chromatin, since ARID1, which is involved in chromatin remodeling, has been shown to bind chromatin within these regions (Zheng et al, 2014).…”

“…On the contrary, there is evidence that the ARID1 protein has a positive influence on DUO1 promoter activity in Arabidopsis. ARID1 is reported to bind the DUO1 promoter in a region approximately 2600 to 2300 bp upstream of the ATG, and in the absence of ARID1, the expression of DUO1 is reduced (Zheng et al, 2014). Since ARID1 is expressed in microspores and vegetative cells (Zheng et al, 2014) it is unlikely to be required for the germline-specific activation of DUO1.…”

“…ARID1 is reported to bind the DUO1 promoter in a region approximately 2600 to 2300 bp upstream of the ATG, and in the absence of ARID1, the expression of DUO1 is reduced (Zheng et al, 2014). Since ARID1 is expressed in microspores and vegetative cells (Zheng et al, 2014) it is unlikely to be required for the germline-specific activation of DUO1. Moreover, reduced H3K9ac levels at the DUO1 promoter in the arid1-1 mutant suggest that ARID1 might act through derepression of DUO1 transcription, rather than through direct activation (Zheng et al, 2014).…”

“…Since ARID1 is expressed in microspores and vegetative cells (Zheng et al, 2014) it is unlikely to be required for the germline-specific activation of DUO1. Moreover, reduced H3K9ac levels at the DUO1 promoter in the arid1-1 mutant suggest that ARID1 might act through derepression of DUO1 transcription, rather than through direct activation (Zheng et al, 2014). Given that sequences in the 2150 bp proximal DUO1 promoter are sufficient to direct male germline-specific transcription , positive transcriptional control mechanisms are likely to control the specificity of DUO1 expression.…”