REGULATION OF FLAVOR METABOLITES IN APPLE IN RESPONSE TO THE SUPPRESSION OF ETHYLENE BIOSYNTHESIS OR ACTION

Bruno G. Defilippi, Gianni Teo, Sandra L. Uratsu, Adel A. Kader and Abhaya M. Dandekar 1Department of Pomology, University of California, Davis, CA 95616.

A salient genetic attribute of tree fruits is the unique blend of sugar, acid, phenolic and volatile components that determine their flavor. This complex genetic trait is manifested in ripe fruit through a complex interaction of metabolic pathways and regulatory circuits that results in the unique fruit flavor composition (FFC), a key t. FFC is key to marketing fresh fruits and their products as it greatly affects consumer preferences, which in turn, impact on the livelihood of fruit growers, and indirectly on the nutritional quality of consumer diets. In order to understand the role of ethylene in regulating the overall flavor of apple fruits, ethylene production or action was reduced using transgenic apple trees suppressed for ACC-synthase or ACC-oxidase enzyme activity, or by the addition of 1-methylcyclopropene (1-MCP), an ethylene action inhibitor. Through these technologies we identified the flavor metabolites that showed ethylene-dependent or ethylene-independent regulation, which are reported in this poster. This new knowledge could lead to the development of more precise diagnostics for quality control leading to a more consistent and high quality fruit for the consumer.

EXPERIMENTAL STRATEGY

RESULTS

GS 61 G

INTRODUCTION

1. SUGARS

-Fruit from transgenic lines and 1-MCP treated fruit did not accumulate sugars to the levels observed in the wild type control (GS).

-In response to ethylene treatment, only the transgenic fruit reached the levels observed in GS, but not the 1-MCP treated fruit after 14 days at 20°C.

-Interestingly, only sucrose and fructose showed ethylene regulation.

Sugars GS (non-transformed)

68G (ACO-antisense)

At harvest

After 14d at 20°C

At harvest

After 14d at 20°C

After 14d at 20°C with ethyl.

Total 9.2±0.7 11.6±0.6* 9.0±0.5 9.6±0.7 11.1±1.2*

Sucrose 2.2±0.4 3.7±0.3* 2.0±0.2 2.3±0.2 3.5±0.4*

Glucose 2.2±0.2 2.5±0.7 1.9±0.2 2.3±0.2 2.1±1.0

Fructose 4.2±0.6 5.4±0.4* 5.1±0.2 5.0±0.4 5.5±0.5*

3. ORGANIC ACIDS

- Down-regulation of ethylene biosynthesis and action significantly reduced the loss of malic and citric acids.

-The main cause of organic acids degradation in climacteric fruit is the increase in respiration rate during ripening, which was significantly reduced under these conditions.

2. PHENOLIC COMPOUNDS

-Phenolic compounds showed ethylene-dependent regulation only in the transgenic lines, but not in the 1-MCP treated fruit or with exposure to ethylene during 14 days at 20°C.

-Therefore, it seems early stages of development are important in phenolic compounds biosynthesis and ethylene may have a role.

Phenolic compounds

GS(non-transformed)

68G (ACO-antisense)

At harvest After 14 d at 20°C At harvest After 14 d at 20°C After 14 d at 20°C with ethyl.

Total 1023 1300* 1100 1150 1100

Chlorogenic acid 158 190* 160 153 170

Phloridzin 23 28 42 37 39

Epicatechin 78 123* 101 100 122

4. AROMA

-Among aroma compounds, esters showed a major reduction in both the transgenic lines and in the 1-MCP treated fruit.

-Supplementation with ethylene only recovered levels of esters in the transgenic lines.

Means follow by (*) are significantly different relative to the evaluation at harvest within individual lines.

Means follow by (*) are significantly different relative to the evaluation at harvest within individual lines.

Bars with (*) are significantly different relative to the evaluation at harvest within individual lines. 68G=ACO antisense; 103Y=ACS sense

Methionine

SAM

ACC

Ethylene

Receptor

ACS

ACO

Ethylene inhibition

Silencing (sense, antisense)

1-MCP

Ethylene enhancement

C2H4

Responses Flavor compounds

Aroma: esters, aldehydes, alcohols

Sweetness: fructose, sucrose, glucose

Acidity: malic acid, citric acid

Astringency: phenolic compounds

ETHYLENE BIOSYNTHESIS

Bars with different letters are significantly different for an individual compound

OBJECTIVE:

The goal this year was to evaluate the role of ethylene in regulating fruit flavor complex at the level of individual metabolites using transgenic apple fruit modified in their capacity to synthesize endogenous ethylene.

FUTURE WORK

-To determine the regulatory role of ethylene in aroma biosynthesis in transgenic apple fruit silenced in their capacity for ethylene biosynthesis.

- To determine the role of ethylene in texture development and accumulation of carbohydrates and acids in transgenic apple fruit silenced for ethylene biosynthesis.