Lipoxygenase Is Involved in the Control of Potato Tuber Development

Abstract

Plant lipoxygenases (LOXs) are a functionally diverse class of dioxygenases implicated in physiological processes such as growth, senescence, and stress-related responses. LOXs incorporate oxygen into their fatty acid substrates and produce hydroperoxide fatty acids that are precursors of jasmonic acid and related compounds. Here, we report the involvement of the tuber-associated LOXs, designated the Lox1 class, in the control of tuber growth. RNA hybridization analysis showed that the accumulation of Lox1 class transcripts was restricted to developing tubers, stolons, and roots and that mRNA accumulation correlated positively with tuber initiation and growth. In situ hybridization showed that Lox1 class transcripts accumulated in the apical and subapical regions of the newly formed tuber, specifically in the vascular tissue of the perimedullary region, the site of the most active cell growth during tuber enlargement. Suppression mutants produced by expressing antisense coding sequence of a specific tuber LOX, designated POTLX-1 , exhibited a significant reduction in LOX activity in stolons and tubers. The suppression of LOX activity correlated with reduced tuber yield, decreased average tuber size, and a disruption of tuber formation. Our results indicate that the pathway initiated by the expression of the Lox1 class genes of potato is involved in the regulation of tuber enlargement. INTRODUCTIONTuber formation in potatoes is a complex developmental process that requires the interaction of environmental, biochemical, and genetic factors. Several important biological processes, such as carbon partitioning, signal transduction, and meristem determination are involved (Ewing and Struik, 1992). Under conditions of a short-day photoperiod and cool temperature, a transmissible signal is activated that initiates cell division and expansion and a change in the orientation of cell growth in the subapical region of the stolon tip (Ewing and Struik, 1992; Xu et al., 1998a). In this signal transduction pathway, perception of the appropriate environmental cues occurs in leaves and is mediated by phytochrome and gibberellins (van den Berg et al., 1995; Jackson and Prat, 1996; Jackson et al., 1996). van den Berg et al. (1996) detected at least 10 quanitative trait loci that control the ability to tuberize under long days, but none of these genes has been identified definitively.Tuber development at the stolon tip consists of biochemical and morphological processes. Both processes are controlled by differential gene expression (Hannapel, 1991; Bachem et al., 1996; Macleod et al., 1999), and most of the research in this area has focused on the biochemical processes, including starch synthesis (Abel et al., 1996;Preiss, 1996; Geigenberger et al., 1998) and storage protein accumulation (Mignery et al., 1984; Hendriks et al., 1991;Suh et al., 1991). Much less is known about the morphological controls of tuberization, although it is clear that phytohormones play a prominent role (Koda et al., 1991; Xu et al., 1998b;Sergeeva et ...

Plant Lipoxygenases. Physiological and Molecular Features

“…Tubers that formed were misshapen and small. These results suggest that LOXs are involved in the control of tuber growth and development, probably by initiating the synthesis of oxylipins that regulate cell growth during tuber formation (Kolomiets et al, 2001).…”

“…The analysis of the phenotype of the antisense LOX transgenic potato plants demonstrates that LOXderived products have a critical function during potato tuber development (Kolomiets et al, 2001). Other developmental programs, such as germination and nodule formation, may require oxylipins as sig-…”

“…The production of transgenic plants expressing an antisense, tuber-specific LOX (POTLX-1) gene gave some clues about the function of LOX in potato tubers (Kolomiets et al, 2001). Based on its deduced amino acid sequence, POTLX-1 belongs to class 1 of LOXs in potato, which are expressed in tubers and roots and have predominantly LOX-9 activity.…”

“…In addition, LOX has been associated with some processes in a number of developmental stages (Siedow, 1991;Kolomiets et al, 2001), and with the mobilization of storage lipids during germination (Feussner et al, 2001). LOX is also used as a storage protein during vegetative growth (Fischer et al, 1999;Fig.…”

“…In addition, LOX genes isolated from different plant species show differential organspecific expression (Griffiths et al, 1999;Kolomiets et al, 2001; Table II).…”