Abstract:Summary
Small RNAs are 20–24 nucleotides in length. In plants, small RNAs are classified into microRNAs (miRNAs) and small interfering RNAs (siRNAs), based on their biogenesis and molecular features. In contrast to the extensive knowledge of the roles of small RNAs in sporophytic tissues, the distribution and function of small RNAs in gametophytic cells have been less well studied. However, with the improvement of single‐cell sorting and RNA sequencing technologies, the distribution of small RNAs, especially s… Show more
“…Similarly, miR165/166 precursors were transcribed mainly in the endodermis of Arabidopsis root, but mature miR166 were observed in adjacent cell layers (Carlsbecker et al , ). These and other examples are consistent with the cell‐to‐cell movement of miRNA (Chitwood et al, 2009; Martínez et al, ; Wu and Zheng, ) (see Figure a).…”
Section: Short‐ and Long‐distance Movement Of Small Rnas In Plants Ansupporting
RNA interference is a biological process whereby small RNAs inhibit gene expression through neutralizing targeted mRNA molecules. This process is conserved in eukaryotes. Here, recent work regarding the mechanisms of how small RNAs move within and between organisms is examined. Small RNAs can move locally and systemically in plants through plasmodesmata and phloem, respectively. In fungi, transportation of small RNAs may also be achieved by septal pores and vesicles. Recent evidence also supports bidirectional cross‐kingdom communication of small RNAs between host plants and adapted fungal pathogens to affect the outcome of infection. We discuss several mechanisms for small RNA trafficking and describe evidence for transport through naked form, combined with RNA‐binding proteins or enclosed by vesicles.
“…Similarly, miR165/166 precursors were transcribed mainly in the endodermis of Arabidopsis root, but mature miR166 were observed in adjacent cell layers (Carlsbecker et al , ). These and other examples are consistent with the cell‐to‐cell movement of miRNA (Chitwood et al, 2009; Martínez et al, ; Wu and Zheng, ) (see Figure a).…”
Section: Short‐ and Long‐distance Movement Of Small Rnas In Plants Ansupporting
RNA interference is a biological process whereby small RNAs inhibit gene expression through neutralizing targeted mRNA molecules. This process is conserved in eukaryotes. Here, recent work regarding the mechanisms of how small RNAs move within and between organisms is examined. Small RNAs can move locally and systemically in plants through plasmodesmata and phloem, respectively. In fungi, transportation of small RNAs may also be achieved by septal pores and vesicles. Recent evidence also supports bidirectional cross‐kingdom communication of small RNAs between host plants and adapted fungal pathogens to affect the outcome of infection. We discuss several mechanisms for small RNA trafficking and describe evidence for transport through naked form, combined with RNA‐binding proteins or enclosed by vesicles.
“…After the second pollen mitosis, ARID1 is absent in sperm cells due to the repression of MET1 (Li et al, 2017), and the siRNA/AGO9 cargo recruits the heterochromatic machinery to maintain heterochromatic silencing. The finding that DDM1 and MET1, two essential factors responsible for TE silencing, exhibit sperm-specific accumulation in pollen (Borges et al, 2008;Slotkin et al, 2009;Li et al, 2017) indicates that the differential regulation of chromatin between the companion cell and the germline could be the consequence of specific spatiotemporal expression patterns of these key epigenetic regulators during plant gametogenesis (Wu & Zheng, 2019). Together with our previous findings that ARID1 functionally associates with histone deacetylases (HDACs; Zheng et al, 2014) and MET1 (Li et al, 2017), we hypothesize that the function of ARID1 might be related to epigenetic regulation during plant reproductive development.…”
Summary
In the plant male germline, transposable elements (TEs) are reactivated in the companion vegetative nucleus, resulting in siRNA production and the intercellular movement of these siRNAs to reinforce TE silencing in sperm. However, the mechanism by which siRNA movement is regulated remains unexplored.
Here we show that ARID1, a transcription factor which is constitutively expressed in the vegetative nucleus but dynamically accumulates in the generative cell (the progenitor of sperm) to promote the second pollen mitosis, mediates siRNA movement to reinforce heterochromatic silencing in the male germline.
We looked for regulators involved in the accumulation of ARID1 in the generative cell, and found that AGO9, a germline‐specific AGO in Arabidopsis, is required for the accumulation of ARID1 in the generative cell. Mutations in either ARID1 or AGO9 lead to the interruption of not only the second pollen mitosis but also the movement of siRNA from the vegetative nucleus to the male germline, resulting in the release of heterochromatic silencing in the male germline. Moreover, conditional knockdown of ARID1 in the generative cell causes reduced heterochromatic silencing in both bicellular and mature pollen.
This study provides insights into how a spatiotemporal transcription factor coordinates heterochromatic silencing and male germline maturation.
“…Finally, epigenetic mechanisms involving small RNAs, in particular siRNAs, are relevant during plant reproduction, for example during a phase of global reactivation of TEs in gametes. During this stage an intercellular movement of siRNAs between companion cells and male gametic cells has been observed, and recent studies have elucidated the function of sperm‐delivered siRNAs during early seed development (reviewed by Wu & Zheng, 2019). ‘Our understanding of the control and function of structural modifications to DNA has, in recent years, been complemented by developmental and ecological perspectives of epigenetics.’…”
Section: Epigenetics and Plant Developmentmentioning
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