MOLECULAR MECHANISMS REGULATING ABA HOMEOSTASIS IN POTATO TUBERS: I. EFFECTS OF POSTHARVEST STORAGE AND DORMANCY STATUS ON ABA CONTENT, METABOLISM, AND EXPRESSION OF GENES INVOLVED IN ABA BIOSYNTHESIS AND METABOLISM.

Authors: Destefano Beltran, Luis; Knauber, Donna; Young, Linda; Suttle, Jeffrey

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2006
Publication Date: 8/1/2006
Citation: Destefano Beltran, L.J., Knauber, D.C., Huckle, L.L., Suttle, J.C. 2006. Effects of postharvest storage and dormancy status an ABA content, metabolism, and expression of genes involved in ABA biosynthesis and metabolism in potato tuber tissues. Plant Molecular Biology. 61(4-5):687-697.

Interpretive Summary: For an indeterminate period of time following harvest, potatoes will not sprout and are physiologically dormant. Dormancy is gradually lost during postharvest storage and the resultant sprouting is detrimental to the nutritional and processing qualities of potatoes. Because of this, sprouting results in severe financial loss to producers. Currently sprouting is controlled through the use of synthetic sprout inhibitors. The research being conducted in this lab is directed towards 1.) identifying key physiological processes that naturally regulate tuber dormancy and, ultimately, 2.) modifying these processes genetically thereby eliminating the need for artificial sprout suppression. The plant hormone abscisic acid (ABA) is the principal regulator of tuber dormancy initiation and maintenance. The internal processes controlling ABA content in tubers are unknown. In this paper, genes encoding the entire ABA biosynthetic pathway and 3 genes involved in ABA destruction have been cloned from potato tubers and the effects of postharvest storage on the contents of each of these genes have been determined using the highly sensitive technique of quantitative real-time polymerase chain reaction (qRT-PCR). In general, levels of ABA biosynthetic genes were highest during early storage when ABA content was highest. As storage continued and ABA content fell, levels of most biosynthetic genes declined while levels of genes encoding enzymes of ABA destruction increased. These results suggest that ABA content during tuber dormancy is controlled by a balance of synthesis and destruction.

Technical Abstract: At harvest, and for an indeterminate period thereafter, potato tubers will not sprout and are physiologically dormant. Abscisic acid (ABA) has been shown to play a critical role in tuber dormancy control but the mechanisms controlling ABA content during dormancy as well as the site of ABA synthesis and catabolism are unknown. As a first step in defining the sites of synthesis and cognate processes regulating ABA turnover during storage and dormancy progression, gene sequences encoding the entire ABA biosynthetic pathway and three catabolism-related genes were used to quantify changes in their relative mRNA abundances in three specific tuber tissues (meristems, their surrounding periderm and underlying cortex) by qRT-PCR. The entire suite of ABA biosynthetic genes was expressed in all three tissues. In general, their expression exhibited a biphasic pattern with transient increases during early and mid-storage. Expression of two members of the potato 9-cis-epoxycarotenoid dioxygenase (NCED) gene family was found to correlate with changes in ABA content in meristems (StNCED2) and cortex (StNCED1). Conversely, expression patterns of three putative ABA-8’-hydroxylase (CYP707A) genes during storage varied in a tissue-specific manner with expression of two of these genes rising in meristems and periderm and declining in cortex during storage. These results suggest that ABA synthesis and metabolism occur in all tuber tissues examined and that tuber ABA content during dormancy is the result of a balance of synthesis and metabolism that increasingly favors catabolism as dormancy ends and may be controlled at the level of StNCED and StCYP707A gene activities.