Abstract

Female gamete development in Arabidopsis ovules comprises two phases. During megasporogenesis, a somatic ovule cell differentiates into a megaspore mother cell and undergoes meiosis to produce four haploid megaspores, three of which degrade. The surviving functional megaspore participates in megagametogenesis, undergoing syncytial mitosis and cellular differentiation to produce a multicellular female gametophyte containing the egg and central cell, progenitors of the embryo and endosperm of the seed. The transition between megasporogenesis and megagametogenesis is poorly characterised, partly owing to the inaccessibility of reproductive cells within the ovule. Here, laser capture microdissection was used to identify genes expressed in and/or around developing megaspores during the transition to megagametogenesis. ARGONAUTE5 (AGO5), a putative effector of small RNA (sRNA) silencing pathways, was found to be expressed around reproductive cells during megasporogenesis, and a novel semi-dominant ago5-4 insertion allele showed defects in the initiation of megagametogenesis. Expression of a viral RNAi suppressor, P1/Hc-Pro, driven by the WUSCHEL and AGO5 promoters in somatic cells flanking the megaspores resulted in a similar phenotype. This indicates that sRNA-dependent pathways acting in somatic ovule tissues promote the initiation of megagametogenesis in the functional megaspore. Notably, these pathways are independent of AGO9, which functions in somatic epidermal ovule cells to inhibit the formation of multiple megaspore-like cells. Therefore, one somatic sRNA pathway involving AGO9 restricts reproductive development to the functional megaspore and a second pathway, inhibited by ago5-4 and P1/Hc-Pro, promotes megagametogenesis.

Links

Publisher Full Text

Authors

Tucker MR, Okada T, Hu Y, Scholefield A, Taylor JM, Koltunow AM

Institution

CSIRO Plant Industry, Waite Campus, Hartley Grove, Urrbrae, SA 5064, Australia.

Source

Development (Cambridge, England) 139:8 2012 Apr pg 1399-404

MeSH

Alleles
Animals
Arabidopsis
Arabidopsis Proteins
Argonaute Proteins
Endosperm
Female
Flowers
Gene Expression Regulation, Developmental
Genes, Plant
Mitosis
Models, Biological
Oligonucleotide Array Sequence Analysis
Phenotype
RNA Interference
RNA, Plant
RNA-Binding Proteins
Seeds

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

22399683