Structural, Functional, and Phylogenetic Characterization of a Large CBF Gene Family in Barley

Abstract

CBFs are key regulators in the Arabidopsis cold signaling pathway. We used Hordeum vulgare (barley), an important crop and a diploid Triticeae model, to characterize the CBF family from a low temperature tolerant cereal. We report that barley contains a large CBF family consisting of at least 20 genes (HvCBFs) comprising three multigene phylogenetic groupings designated the HvCBF1-, HvCBF3-, and HvCBF4-subgroups. For the HvCBF1- and HvCBF3-subgroups, there are comparable levels of phylogenetic diversity among rice, a cold-sensitive cereal, and the cold-hardy Triticeae. For the HvCBF4-subgroup, while similar diversity levels are observed in the Triticeae, only a single ancestral rice member was identified. The barley CBFs share many functional characteristics with dicot CBFs, including a general primary domain structure, transcript accumulation in response to cold, specific binding to the CRT motif, and the capacity to induce cor gene expression when ectopically expressed in Arabidopsis. Individual HvCBF genes differed in response to abiotic stress types and in the response time frame, suggesting different sets of HvCBF genes are employed relative to particular stresses. HvCBFs specifically bound monocot and dicot cor gene CRT elements in vitro under both warm and cold conditions; however, binding of HvCBF4-subgroup members was cold dependent. The temperature-independent HvCBFs activated cor gene expression at warm temperatures in transgenic Arabidopsis, while the cold-dependent HvCBF4-subgroup members of three Triticeae species did not. These results suggest that in the Triticeae - as in Arabidopsis - members of the CBF gene family function as fundamental components of the winter hardiness regulon.

Large deletions in the CBF gene cluster at the Fr-B2 locus are associated with reduced frost tolerance in wheat

“…Whereas Arabidopsis has three CBF genes present as a tandem cluster, wheat and other members of the Pooideae family have undergone a large expansion of this gene family, with eleven genes at the Fr-2 locus, eight of which are Pooideae-specific (Badawi et al 2007;Miller et al 2006;Skinner et al 2005). This expansion has been dated to coincide with a period of global cooling during the Eocene-Oligocene transition approximately 33 MYA (Sandve and Fjellheim 2010) and it has been proposed that the increase in the number of CBF genes and diversity at this locus may have occurred as a result of selection pressure for improved frost tolerance by this period of lower temperatures.…”

Structural and functional characterization of a winter malting barley

“…Fr-H1 and Fr-H2, the main LT tolerance QTL (Francia et al 2004), were located in an introgressed NE76129 region of chromosome 5H (Figure 2). The candidate gene for Fr-H2 is one or more members of two physically linked clusters of at least 11 CBF genes Galiba et al 2009;Skinner et al 2005) whose expression is regulated by Fr-H1 ). Fr-H1 is not only important for LT tolerance at the vegetative stage, but also for reproductive-stage frost tolerance (Reinheimer et al 2004).…”

Hv-CBF2A overexpression in barley accelerates COR gene transcript accumulation and acquisition of freezing tolerance during cold acclimation

“…; and rye, Secale cereale), is much larger than that of Arabidopsis, other dicots, and tropical cereals such as maize (Zea mays) and rice (Oryza sativa). The barley genome harbors more than 20 CBF coding sequences in a single genotype (Skinner et al 2005). At least 13 of these colocalize in a cluster on the long arm of chromosome 5 (Skinner et al 2005(Skinner et al , 2006Miller et al 2006;Badawi et al 2007;Francia et al 2007;Knox et al 2010).…”