Genes associated with chloroplasts and hormone-signaling, and transcription factors other than CBFs are associated with differential survival after low temperature treatments of Camelina sativa biotypes

Authors: Horvath, David; Anderson, James; Chao, Wun; ZHENG, PUYING - North Dakota State University; BUCHWALDT, MILES - Agriculture And Agri-Food Canada; PARKIN, ISOBEL - Agriculture And Agri-Food Canada; DORN, KEVIN - Kansas State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2019
Publication Date: 5/31/2019
Citation: Horvath, D., Anderson, J.V., Chao, W.S., Zheng, P., Buchwaldt, M., Parkin, I.A.P., Dorn, K. 2019. Genes associated with chloroplasts and hormone-signaling, and transcription factors other than CBFs are associated with differential survival after low temperature treatments of Camelina sativa biotypes. PLoS One. 14(5):e0217692. https://doi.org/10.1371/journal.pone.0217692.
DOI: https://doi.org/10.1371/journal.pone.0217692

Interpretive Summary: Camelina sativa (hereafter referred to as camelina) is an emerging oils seed crop that has potential for use as a cover crop and/or use in dual-cropping systems in the Norther Great Plains of the U.S. However, freezing damage can limit the yield of this crop. Previous work showed that there were two types (biotypes) of camelina. One, a summer biotype, can be planted in the spring and produces seeds the same year. A second one is a winter biotype that is planted in the fall, and must experience a period of long term cold in order to flower and set seeds the following spring. Here, we provide evidence that a winter biotype called Joelle, is far better at surviving freezing conditions than a summer biotype named CO46. We bred these two biotypes with each other, and by counting the number of resulting seedlings that were either highly tolerant to freezing conditions or that were easily killed by freezing, we determined that there were as few as two genes that seemed to control this trait. We then looked to see what genes were turned on or off in these two biotypes before and after cold treatments to see if we could find differences that might explain why these two biotypes have such differing abilities to withstand freezing conditions. We found several genes of interest, including a few that are known to produce proteins called transcription factors. Transcription factors can turn many other genes on or off and can have a large effect on how plants deal with freezing temperatures. Several of these transcription factor genes are likely involved in photosynthesis. This is interesting since one of the most damaging effects of freezing occurs when photosynthesis does not work correctly, and chemicals are produced that can damage the cell. Photosynthesis does not always work correctly in the cold, but many plants can swap out different photosynthesis proteins so that it works better in the cold and fewer damaging chemicals are produced. Other genes that were turned on or off differently in the two biotypes appear to also be involved in sensing damage specifically caused by the chemicals produced when photosynthesis does not work right. One of the more surprising observations was that a gene that has long been known to control the ability to reduce freezing damage and has been used to engineer more freezing tolerant plants was turned on in both biotypes. This study provides scientists with new genes to modify that may allow summer biotypes of camelina to survive freezing conditions as well as the winter biotype Joelle.

Technical Abstract: Winter annual biotypes of Camelina sativa regularly survive after freezing conditions experienced in northern regions of the U.S., whereas summer annual biotypes do not. To determine potential molecular mechanisms associated with these biotype differences in survival after freezing treatments, we examined genetic and transcript variations in both a winter- (Joelle) and a summer- (CO46) biotype. We determined that there may be as few as 2 dominant genes controlling survival after freezing treatments. We also identified 1797 genes that were differentially expressed in response to cold in both the winter and summer biotypes. Among these were many COR genes, indicating that the CBF regulon is functional in both. However, only 153 and 76 genes from Joelle and CO46, respectively, were either differentially expressed or were off in one biotype verses the other following cold acclimation. We hypothesize that these 229 genes play a significant role in, or are primarily responsive to, differences in survival after freezing between these two biotypes. Promoter analysis provided few clues as to the regulation or these genes; however, genes that were down-regulated specifically in the winter biotype Joelle were enriched with the sequence TGGCCCTCGCTCAC, which is over-represented among genes associated with chloroplasts in Arabidopsis. Additionally, several genes involved in auxin signaling were down-regulated specifically in Joelle. A transcription factor with strong similarity to MYB47, known to be up-regulated by salt, drought, and jasmonic acid, but not cold in Arabidopsis, was essentially off in the freezing sensitive biotype CO46, but was cold-induced in the winter biotype Joelle. Several other transcription factors genes including three with similarity to WRKY70, that may be involved of SA/JA-dependent responses, a HOMEOBOX 6 gene involved in ABA signaling, and two others (NUCLEAR FACTOR Y and CONSTANS-like 2) known to be implicated in photoperiodic flowering were also differentially expressed between the two biotypes.