Wound-induced suberization genes are differentially expressed, patially and temporally, during closing layer and wound periderm formation

Authors: Lulai, Edward; Neubauer, Jonathan

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2013
Publication Date: 4/1/2014
Citation: Lulai, E.C., Neubauer, J. 2014. Wound-induced suberization genes are differentially expressed, spatially and temporally, during closing layer and wound periderm formation. Postharvest Biology and Technology. 90:24-33.

Interpretive Summary: Potato tuber wounds incurred during harvest, handling into and out of storage and upon seed cutting require rapid suberization as a major part of the wound-healing processes to prevent infection, desiccation, defect development and loss of nutritional value. The induction and regulation of rapid suberization of wounds is of great economic importance. Wound related losses cost growers, processors and storage operators well over $300 million/year; this does not include losses that are difficult to quantify from problems such as tuber pine eye, pink rot or losses incurred by the grocer and consumer. Despite the large economic and nutritional importance of tuber wound-healing, little is known about the molecular mechanisms and related genes controlling these processes and how they are expressed during the two major stages of wound-induced suberization, i.e. closing layer formation followed by wound periderm formation. In this paper we identify the developmental time course for closing layer and wound periderm formation, determine the pattern of accumulation of the two suberin biopolymers that compose the suberin barrier to infection and determine the expression profiles of specific genes involved in wound-induced suberization. Although both stages critically involve suberization, they differ in that closing layer development requires rapid suberization of existing parenchyma cells bordering the wound surface to provide the initial protective barrier for the wound; whereas wound periderm development occurs later, i.e. after completion of the closing layer, and requires phellogen-mediated formation of highly organized files containing several layers of suberized wound-phellem cells that provide a more durable protective suberized barrier for the tuber. The processes delineating these two important stages of wound-induced suberization are poorly understood. This research shows that, unlike some wound responding genes such as phenylalanine ammonia lyase (StPAL-1) and anionic peroxidase (StPrx), certain genes that are specifically dedicated to suberization and involved in both of these processes do not remain uniformly up-regulated during the two stages of healing. Genes that do not remain uniformly up-regulated during wound-induce suberization include StTHT encoding Hydroxycinnamoyl-CoA:tyramine N-(hydroxycinnamoyl)transferase, StFHT encoding a fatty '-hydroxyacid/fatty alcohol hydroxycinnamoyl transferase, StKCS6 encoding a 3-ketoacyl-CoA synthase, StFAOH encoding a fatty acid '-hydroxylase and StGPAT5 encoding a protein with acyl-CoA:glycerol-3-phosphate acyltransferase. Instead, these genes are up-regulated during closing layer formation; i.e. starting by about 1 day after wounding, but then slightly down-regulate or pause near completion of the closing layer (about 5-6 days after wounding) and then again up-regulate as wound periderm development is fully initiated (about 7 days after wounding). This interlude in the expression profiles of suberization genes was not anticipated and had not been demonstrated previously, but was repeated herein using minitubers from two different crop years. These results demonstrate that although the two stages of suberization are distinctly separate, they are linked by wound related signals that are coupled in some yet to be determined fashion. Most importantly, the results show that genes critically involved in the suberization of the two stages are closely regulated to recognize the suberization processes as separate, despite the smooth programed transition from closing layer to wound periderm development. The biology of this differential is important because of the roles closing layer and wound periderm development respectively play in rapid and long term protection of the tuber from disease and other challenges. This information is mechanistically important in the development of new

Technical Abstract: Potato tuber (Solanum tuberosum L.) wounds incurred at harvest and upon seed cutting require rapid suberization as a major part of the healing process to prevent infection and desiccation. However, little is known about the induction and expression of genes that are essential for these processes and in particular to the two major stages of wound-induced suberization, i.e. closing layer formation and wound periderm formation. The objectives of this research were to address these needs by determining the effects of wounding on the induction and expression profiles of specific genes involved in wound-induced suberization in potato tuber (Solanum tuberosum L.) during the initiation and completion of closing layer formation and wound periderm formation. Although both stages critically involve suberization, there are significant differences between the two processes. Closing layer development requires rapid suberization of existing parenchyma cells bordering the wound surface to provide the initial protective barrier for the wound. Wound periderm development occurs later, i.e. after completion of closing layer formation, and requires development of a wound phellogen layer which mediates the formation of highly organized files of suberized wound-phellem cells that provide a more durable protective barrier for the tuber. The processes delineating these two separate stages of wound-induced suberization are poorly understood. This research shows that, unlike some wound responding genes such as phenylalanine ammonia lyase (StPAL-1) and anionic peroxidase (StPrx), certain genes that are specifically involved in both of these processes do not remain uniformly up-regulated during the two stages of healing (i.e. StTHT encoding Hydroxycinnamoyl-CoA:tyramine N-(hydroxycinnamoyl)transferase, StFHT encoding a fatty '-hydroxyacid/fatty alcohol hydroxycinnamoyl transferas, StKCS6 encoding a 3-ketoacyl-CoA synthase, StFAOH encoding a fatty acid '-hydroxylase and StGPAT5 encoding a protein with acyl-CoA:glycerol-3-phosphate acyltransferase). Instead, they are up-regulated during closing layer formation; i.e. starting by ca. 1 day after wounding, but then slightly down-regulated or pause near completion of the closing layer (ca. 5-6 days) and then again up-regulated as wound periderm development is fully initiated (ca. 7 days) and down-regulate near completion (ca. 28 days after wounding). This differential in the expression profile, i.e. decrease between stages, was not anticipated and may be the first demonstration of measurable changes of any sort of biological flux as wound induced suberization transitions from closing layer to wound periderm development. Results were repeated using minitubers from two different crop years and demonstrate that these processes are separate, but coupled in some yet to be determined fashion. The biology of this differential expression is important because of the roles closing layer and wound periderm development play in protecting the tuber from disease and other challenges.