The Brittle Rachis Trait in Species Belonging to the Triticeae and Its Controlling Genes Btr1 and Btr2

Abstract

In many non-cultivated angiosperm species, seed dispersal is facilitated by the shattering of the seed head at maturity; in the Triticeae tribe, to which several of the world's most important cereals belong, shattering takes the form of a disarticulation of the rachis. The products of the genes Btr1 and Btr2 are both required for disarticulation to occur above the rachis nodes within the genera Hordeum (barley) and Triticum/Aegilops (wheat). Here, it has been shown that both Btr1 and Btr2 are specific to the Triticeae tribe, although likely paralogs (Btr1-like and Btr2-like) are carried by the family Poaceae including Triticeae. Aegilops tauschii (the donor of the bread wheat D genome) lacks a copy of Btr1 and disarticulation in this species occurs below, rather than above the rachis node; thus, the product of Btr1 appears to be required for disarticulation to occur above the rachis node.

The Ectopic Expression of Btr2 in Aegilops tauschii Switches the Disarticulation Layer From Above to Below the Rachis Node

“…tauschii ssp. strangulata is thought to be responsible for the presence of two copies of Btr2 (Zeng et al, 2020b). Both Btr2 copies of Ae.…”

“…php shows the same result. The origin of Btr2 and Btr2-like dates back to an ancient duplication event (Pourkheirandish et al, 2015), which occurred in the common ancestor of the Triticeae tribe (Zeng et al, 2020b).…”

“…The presence on chromosome arm 3HS of the dominant, complementary and tightly linked genes Btr1 and Btr2 is necessary for the expression of the trait in wild forms of Hordeum vulgare (barley; Pourkheirandish et al, 2015). In Triticum and Aegilops species, Btr1 and Btr2 map to the short arm of the group 3 homeolog (Avni et al, 2017;Zeng et al, 2020b). The products of this pair of genes are presumed to determine the unique mode of disarticulation exhibited by the Aegilops longissima spike, in which only one or two of the central nodes are brittle (Zeng et al, 2020a).…”

“…A comparison of the Btr1 and Btr2 sequences harbored by a range of grass species has shown that while Ae. tauschii lacks an intact copy of Btr1, two copies of Btr2 are present, both of which map along chromosome arm 3DS (Zeng et al, 2020b). Since Btr1 and Btr2 act as a complementary gene pair in most Triticeae species, Ae.…”

The abscission regulatory module INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) / HAESA (HAE)-like receptor kinases in Solanaceae species: Functional analysis in Nicotiana benthamiana

“…And two different loci, brittle-rachis 1 (Btr1) and brittle-rachis 2 (Btr2), encoding an α/β-hydrolase superfamily protein and a hypothetical protein, respectively, have been involved in the regulation of brittle rachis (seed shattering) in barley (Pourkheirandish et al, 2015). Homologs of these two genes, Btr1 and Btr2, are also active in two wild wheat relatives, Aegilops longissima and Aegilops tauschii, which also result in seed shattering phenotypes (Zeng et al, 2020a;Zeng et al, 2020b;Zeng et al, 2020c).…”