Engineering carpel-specific cold stress tolerance: a case study in Arabidopsis

Authors: Artlip, Timothy - Tim; Wisniewski, Michael; TAKATSUJI, HIROSHI - National Institute Of Agrobiological Sciences (NIAS); Bassett, Carole

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2015
Publication Date: 7/16/2016
Citation: Artlip, T.S., Wisniewski, M.E., Takatsuji, H., Bassett, C.L. 2016. Engineering carpel-specific cold stress tolerance: a case study in Arabidopsis. Physiologia Plantarum. 157:469-478.

Interpretive Summary: Floral buds of many horticulturally important species experience changes in sensitivity to low or freezing temperatures depending on when such temperatures occur during the annual growth cycle. Such temperatures generally do not cause injury during winter when the buds are dormant. Once the buds are released from dormancy during spring, they are especially vulnerable to freezing temperatures. The carpel, a floral organ, is the most susceptible part of the flower. Late spring frosts, in particular, can be devastating, particularly if the frost coincides with the bloom. A late spring frost in 2007 completely destroyed the peach crop in several states. A type of protein, called a dehydrin, has been shown to protect cellular components from freezing temperatures. While dehydrins are found in many plant tissues including seeds, roots, leaves and bark, they are not found in carpels. One strategy to mitigate late spring frosts is to express dehydrins in the carpels. This study used the commonly-used experimental plant, Arabidopsis thaliana, in which to over-express a dehydrin originally characterized from peach. The peach dehydrin has been shown to be cold regulated and to preserve the function of a freezing-sensitive enzyme. A commonly used freezing test, electrolyte leakage, was modified to use carpels. We found that Arabidopsis carpels that over-express the peach dehydrin gain as much as a 1.9 degrees C (3.4 degrees F) improvement in freezing tolerance. Such an improvement is significant when only a few degrees can mean the difference between a decent crop and no crop.

Technical Abstract: Freezing temperatures during winter generally do not injure floral buds of horticulturally important crops. Entry into dormancy coupled with cold acclimation provides adequate protection unless the temperatures are exceptionally low. This measure of protection is lost in spring when the floral buds exit from dormancy and deacclimate. The most freezing-susceptible floral organ is the carpel, especially during bloom. Warm temperatures followed by late spring frosts can be devastating, as seen in the Easter freeze of 2007, when several states reported a complete loss of the peach crop. Moreover, climate change models predict that such events may become more commonplace. A potential mitigating strategy would be to over-express some protective protein or compound. Dehydrins are proteins that have been shown to protect sub-cellular components such as membranes along with bio-molecules such as DNA and other proteins from the deleterious effects of dehydration, and freezing is inherently dehydrative. These proteins can be found in many tissues ranging from seeds to leaves to bark. The peach (Prunus persica) dehydrin PpDhn1 gene was found to be highly responsive to low temperatures, while the cognate protein was found to have cryoprotective activity with a freezing-sensitive enzyme. In the present study, PpDhn1 was driven by a carpel-specific promoter, ZPT2-10, from petunia (Petunia hybrid) in transformed Arabidopsis thaliana. Multiple transgenic lines were examined, and transformants displaying flower-specific PpDhn1 expression were chosen for further examination. Line 1-20 was selected for evaluation. A carpel-specific ion leakage assay was developed to assess freezing tolerance. It was found that non-cold-acclimated Line 1-20 had as much as a 1.9 degrees C improvement in freezing tolerance compared to untreated non-transformed controls. This result is significant considering that most reports citing an improvement in freezing tolerance using an over-expressed dehydrin gene or genes only saw improvements in cold-acclimated plants.