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.

Many plants increase in freezing tolerance in response to low, nonfreezing temperatures, a phenomenon known as cold acclimation. Cold acclimation in Arabidopsis involves rapid cold-induced expression of the C-repeat/dehydrationresponsive element binding factor (CBF) transcriptional activators followed by expression of CBF-targeted genes that increase freezing tolerance. Here, we present evidence for a CBF cold-response pathway in Brassica napus. We show that B. napus encodes CBF-like genes and that transcripts for these genes accumulate rapidly in response to low temperature followed closely by expression of the cold-regulated Bn115 gene, an ortholog of the Arabidopsis CBF-targeted COR15a gene. Moreover, we show that constitutive overexpression of the Arabidopsis CBF genes in transgenic B. napus plants induces expression of orthologs of Arabidopsis CBF-targeted genes and increases the freezing tolerance of both nonacclimated and cold-acclimated plants. Transcripts encoding CBF-like proteins were also found to accumulate rapidly in response to low temperature in wheat (Triticum aestivum L. cv Norstar) and rye (Secale cereale L. cv Puma), which cold acclimate, as well as in tomato (Lycopersicon esculentum var. Bonny Best, Castle Mart, Micro-Tom, and D Huang), a freezing-sensitive plant that does not cold acclimate. An alignment of the CBF proteins from Arabidopsis, B. napus, wheat, rye, and tomato revealed the presence of conserved amino acid sequences, PKK/RPAGRxKFxETRHP and DSAWR, that bracket the AP2/EREBP DNA binding domains of the proteins and distinguish them from other members of the AP2/EREBP protein family. We conclude that components of the CBF cold-response pathway are highly conserved in flowering plants and not limited to those that cold acclimate.Plants vary greatly in their abilities to survive freezing temperatures (Sakai and Larcher, 1987). Whereas plants from tropical regions have essentially no capacity to withstand freezing, herbaceous plants from temperate regions can survive freezing at temperatures ranging from Ϫ5 to Ϫ30°C, depending on the species. It is significant that the maximum freezing tolerance of plants is not constitutive, but is induced in response to low temperatures (below approximately 10°C), a phenomenon known as "cold acclimation" (Hughes and Dunn, 1996;Thomashow, 1999). Nonacclimated wheat (Triticum aestivum L. cv Norstar) plants, for instance, are killed at freezing temperatures of about Ϫ5°C, but after cold acclimation, can survive temperatures down to about Ϫ20°C. Determining what accounts for the differences in freezing tolerance between plant species and the molecular basis of cold acclimation is of basic scientific interest and has the potential to provide new approaches to improve the freezing tolerance of plants, an important agronomic trait.A recent advance in understanding cold acclimation in Arabidopsis was the discovery of the C-repeat/dehydration-responsive element binding factor (CBF) cold-response pathway (see Thomashow, 2001). Arabidopsis encodes a small fami...

BackgroundAphid infestation of switchgrass (Panicum virgatum) has the potential to reduce yields and biomass quality. Although switchgrass-greenbug (Schizaphis graminum; GB) interactions have been studied at the whole plant level, little information is available on plant defense responses at the molecular level.ResultsThe global transcriptomic response of switchgrass cv Summer to GB was monitored by RNA-Seq in infested and control (uninfested) plants harvested at 5, 10, and 15 days after infestation (DAI). Differentially expressed genes (DEGs) in infested plants were analyzed relative to control uninfested plants at each time point. DEGs in GB-infested plants induced by 5-DAI included an upregulation of reactive burst oxidases and several cell wall receptors. Expression changes in genes linked to redox metabolism, cell wall structure, and hormone biosynthesis were also observed by 5-DAI. At 10-DAI, network analysis indicated a massive upregulation of defense-associated genes, including NAC, WRKY, and MYB classes of transcription factors and potential ancillary signaling molecules such as leucine aminopeptidases. Molecular evidence for loss of chloroplastic functions was also detected at this time point. Supporting these molecular changes, chlorophyll content was significantly decreased, and ROS levels were elevated in infested plants 10-DAI. Total peroxidase and laccase activities were elevated in infested plants at 10-DAI relative to control uninfested plants. The net result appeared to be a broad scale defensive response that led to an apparent reduction in C and N assimilation and a potential redirection of nutrients away from GB and towards the production of defensive compounds, such as pipecolic acid, chlorogenic acid, and trehalose by 10-DAI. By 15-DAI, evidence of recovery in primary metabolism was noted based on transcript abundances for genes associated with carbon, nitrogen, and nutrient assimilation.ConclusionsExtensive remodeling of the plant transcriptome and the production of ROS and several defensive metabolites in an upland switchgrass cultivar were observed in response to GB feeding. The early loss and apparent recovery in primary metabolism by 15-DAI would suggest that these transcriptional changes in later stages of GB infestation could underlie the recovery response categorized for this switchgrass cultivar. These results can be exploited to develop switchgrass lines with more durable resistance to GB and potentially other aphids.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-017-0998-2) contains supplementary material, which is available to authorized users.

Field and greenhouse experiments were conducted in Nebraska to (1) confirm the 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting resistant-waterhemp biotype (HPPD-RW) by quantifying the resistance levels in dose-response studies, and (2) to evaluate efficacy of PRE-only, POST-only, and PRE followed by POST herbicide programs for control of HPPD-RW in corn. Greenhouse dose-response studies confirmed that the suspected waterhemp biotype in Nebraska has evolved resistance to HPPD-inhibiting herbicides with a 2-to 18-fold resistance depending upon the type of HPPD-inhibiting herbicide being sprayed. Under field conditions, at 56 d after treatment, ≥90% control of the HPPD-RW was achieved with PRE-applied mesotrione/atrazine/ S-metolachlor + acetochlor, pyroxasulfone (180 and 270 g ai ha −1 ), pyroxasulfone/fluthiacet-methyl/ atrazine, and pyroxasulfone + saflufenacil + atrazine. Among POST-only herbicide programs, glyphosate, a premix of mesotrione/atrazine tank-mixed with diflufenzopyr/dicamba, or metribuzin, or glufosinate provided ≥92% HPPD-RW control. Herbicide combinations of different effective sites of action in mixtures provided ≥86% HPPD-RW control in PRE followed by POST herbicide programs. It is concluded that the suspected waterhemp biotype is resistant to HPPD-inhibiting herbicides and alternative herbicide programs are available for effective control in corn. The occurrence of HPPD-RW in Nebraska is significant because it limits the effectiveness of HPPD-inhibiting herbicides. Nomenclature: Acetochlor, atrazine, glyphosate, clopyralid, dicamba, diflufenzopyr, dimethenamid-P, flumetsulam, fluthiacet-methyl, glufosinate, isoxaflutole, mesotrione, metribuzin, pyroxasulfone S-metolachlor, saflufenacil, rimsulfuron, tembotrione, thiencarbazone-methyl, topramezone, waterhemp, Amaranthus tuberculatus (Moq.) Sauer, corn, Zea mays L. Key words: 4-hydroxyphenylpyruvate dioxygenase, pigment inhibitors, PRE, POST, triketone, weed management, weed resistance. Se realizaron experimentos de campo y de invernadero en Nebraska para (1) confirmar un biotipo de Amaranthus tuberculatus resistente a inhibidores de 4-hydroxyphenylpyruvate dioxygenase (HPPD) (HPPD-RW) cuantificando el nivel de resistencia con estudios de respuesta a dosis, y (2) evaluar la eficacia de programas de herbicidas para el control de HPPD-RW en maíz con sólo herbicidas PRE, sólo POST, y herbicidas PRE seguidos por POST. Los estudios de respuesta a dosis en invernadero confirmaron que el biotipo de A. tuberculatus en Nebraska ha evolucionado resistencia a herbicidas inhibidores de HPPD con 2 a 18 veces mayor resistencia dependiendo del tipo de herbicida inhibidor de HPPD que se aplicó. Bajo condiciones de campo, a 56 d después del tratamiento, se alcanzó ≥90% de control de HPPD RW con aplicaciones PRE de mesotrione/ atrazine/S-metolachlor + acetochlor, pyroxasulfone (180 y 270 g ai ha), pyroxasulfone/fluthiacet-methyl/atrazine, y pyroxasulfone + saflufenacil + atrazine. Entre los programas de herbicidas con sólo POST, glyphosate, una premezcla d...