Divergent gene expression networks underlie morphological diversity of abscission zones in grasses

Abstract

Summary Abscission is a process in which plants shed their parts, and is mediated by a particular set of cells, the abscission zone (AZ). In grasses (Poaceae), the position of the AZ differs among species, raising the question of whether its anatomical structure and genetic control are conserved. The ancestral position of the AZ was reconstructed. A combination of light microscopy, transmission electron microscopy, RNA‐Seq analyses and RNA in situ hybridisation were used to compare three species, two (weedy rice and Brachypodium distachyon) with the AZ in the ancestral position and one (Setaria viridis) with the AZ in a derived position below a cluster of flowers (spikelet). Rice and Brachypodium are more similar anatomically than Setaria. However, the cell wall properties and the transcriptome of rice and Brachypodium are no more similar to each other than either is to Setaria. The set of genes expressed in the studied tissues is generally conserved across species, but the precise developmental and positional patterns of expression and gene networks are almost entirely different. Transcriptional regulation of AZ development appears to be extensively rewired among the three species, leading to distinct anatomical and morphological outcomes.

TheSetaria viridisgenome and diversity panel enables discovery of a novel domestication gene

“…Like other known shattering genes in the grass family (Sh4 30 , qSh1 31 , Shat1 32 in rice, and Sh1 33 in sorghum), SvLes1 is a transcription factor. It is a member of the very large MYB family, a set of genes also implicated in shattering by the comparative study of Yu et al 12 . The precise mechanism of shattering is not known in any cereal, and recent data suggest that each species may have a unique mechanism 12 .…”

“…It is a member of the very large MYB family, a set of genes also implicated in shattering by the comparative study of Yu et al 12 . The precise mechanism of shattering is not known in any cereal, and recent data suggest that each species may have a unique mechanism 12 . Unlike other grasses, the AZ in Setaria viridis is not histologically distinct, with only subtle differences between wild type and domesticated plants 7,8 .…”

“…Setaria italica (foxtail millet) is the domesticated form of S. viridis; like most domesticates it fails to form an AZ and thus is non-shattering 8 . While loss of shattering has been an important early step in the domestication of all cultivated grasses, the genes involved generally differ among species 7,[9][10][11][12] . In particular, genes and QTL identified in rice domestication are, for the most part, not conserved among other species 7,11,12 .…”

“…While loss of shattering has been an important early step in the domestication of all cultivated grasses, the genes involved generally differ among species 7,[9][10][11][12] . In particular, genes and QTL identified in rice domestication are, for the most part, not conserved among other species 7,11,12 . However, most of these studies 5 have compared wild species to domesticates and none have considered the standing variation for reduced shattering in wild accessions.…”

The anatomy of abscission zones is diverse among grass species

“…Despite the knowledge gained from studies of AZ development of model species (Ballester and Ferrándiz, ; Tranbarger et al., ), AZs may be diverse in morphology and developmental regulation (Doust et al., ; Yu and Kellogg, ; Yu et al., ). One example appears in Poaceae (the grass family), which consists of over 12,000 species including all cereal crops such as rice, wheat, and maize, and biofuel crops such as switchgrass (Kellogg, ).…”