ANTISENSE SUPPRESSION OF A BETA-GALACTOSIDASE GENE (TBG6) IN TRANSGENIC TOMATO FRUIT INCREASES FRUIT CRACKING

Authors: Moctezuma, Edgar; Smith, David; Gross, Kenneth

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2003
Publication Date: 9/1/2003
Citation: Moctezuma, E., Smith, D.L., Gross, K.C. 2003. Antisense suppression of a beta-galactosidase gene (tbg6) in transgenic tomato fruit increases fruit cracking. Journal of Experimental Botany, Vol. 54, No. 390, pp. 2025-2033, September 2003

Interpretive Summary: About 25% of all fruits and vegetables are never eaten due to losses that occur after harvest. Because of the critical relationship that deleterious changes in texture have to postharvest quality, we are studying the mechanisms involved in the loss of firmness and elasticity that occur during fruit development. Although fruit elasticity (ability to withstand handling and shipping) may involve a number of mechanisms, it is generally accepted that genetically-programmed changes in the cell wall (sugar envelope surrounding plant cells) are critical. Several enzymes have been identified in tomato fruit which can alter the cell wall. These enzymes are called beta-galactosidases, and each is encoded for by one corresponding gene. Using genetic engineering we were able to suppress the mRNA abundance of the gene TBG6 (antisense). In transgenic tomato plants with very low TBG6 mRNA levels, fruit cracking increased dramatically. This implicates an important role for the TBG6 in tomato fruit elasticity and may lead to the development of tomato lines with crack-resistant fruit while still maintaining other favorable eating characteristics. This will benefit the fresh produce industry and all consumers.

Technical Abstract: Antisense suppression of a tomato beta-galactosidase gene (TBG6) was used to study its role in fruit development, cell wall modification, and fruit firmness. TBG6 mRNA is highly abundant during the early stages of fruit development, but the levels decline sharply after the breaker stage and the start of climacteric ethylene. Two antisense lines were obtained with significantly reduced levels of TBG6 mRNA at all stages of fruit development: at 30 dap TBG6 mRNA levels were reduced by up to 98% and 88% in lines 6-2 and 6-10, respectively. Morphological phenotypes observed in the antisense lines were: increased fruit cracking, reduced locular space, and a doubling in the thickness of the fruit cuticle. Biochemical changes in the antisense lines include reduction of exo-galactanse activity at the breaker plus three stage and a reduction in the cell wall galactosyl content at the 20 dap stage. In addition, transgenic lines exhibited a 35 to 39% reduction in fruit firmness at the 20 dap stage, but their texture regained normal levels at 30 dap and beyond. Although its exact function is still unknown, these results implicate an important role for TBG6 in early fruit growth and development in tomato.