Sporophytic small RNA control of female germline development in Arabidopsis and barley

MR Tucker1, NJ Shirley1,2, BJ Carroll3, AMG Koltunow4, WH Leong1,2 and LG Wilkinson1,2

  1. School of Agriculture, Food and Wine, University of Adelaide, Urrbrae, SA 5064, Australia
  2. ARC Centre of Excellence in Plant Cell Walls, University of Adelaide, Urrbrae, SA 5064, Australia
  3. School of Chemistry & Molecular Biosciences, University of Queensland, Brisbane, Australia
  4. CSIRO Agriculture, Hartley Grove, Waite Campus, Urrbrae, SA 5064, Australia

In plants, formation of the female gamete occurs deep within the ovule and is required for the successful and stable production of seed. Although young reproductive cells in the ovule are difficult to access they provide an excellent opportunity to study pathways involved in developmental transitions and cell fate. Mutants showing altered ovule development indicate that cross-talk between sporophytic and reproductive cells is required for viable gamete production. We previously identified a mutation in ARGONAUTE5 (AGO5) that creates a dominant-negative protein (AGO5dn). AGO5dn acts in the ovule nucellus and inhibits the formation of a female gametophyte, most likely through the inhibition of small RNA-dependent pathways. Similar phenotypes are observed in transgenic plants expressing the pAGO5:P1-HcPRO sRNA suppressor protein, but distinct from the ago9-2 mutant that produces extra female reproductive cells. Changes in transcript abundance in these three backgrounds were assessed using RNAseq. This revealed overlaps with known regulators of megasporogenesis as well as novel pathways potentially involved in intercellular signalling. In recent work we have extended our studies of ovule development into barley, a grain crop of economic importance. Several quantitative trait loci (QTL) that influence ovule size and morphology suggest that similar pathways to those identified in Arabidopsis may be influencing ovule development and function in monocot and dicot species.