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Title: ETHYLENE REGULATES MRNA EXPRESSION OF THREE BETA-GALACTOSIDASE GENES IN WILD TYPE AND MUTANT TOMATO AT THE ONSET OF FRUIT RIPENING

Author
item Moctezuma, Edgar
item Smith, David
item Gross, Kenneth

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2002
Publication Date: 4/14/2003
Citation: Moctezuma, E., Smith, D.L., Gross, K.C. 2002. Ethylene regulates mrna expression of three beta-galactosidase genes in wild type and mutant tomato at the onset of fruit ripening. Postharvest Biology and Technology. 28(2003) 207-217

Interpretive Summary: Fruit softening that occurs during ripening has a major impact on quality and shelf-life of fresh produce. Thus, we have studied the mechanisms involved in the loss of firmness that occurs during tomato fruit ripening. A critical feature of fruit softening is the disassembly of the cell wall (the sugar envelope surrounding plant cells) that occurs during ripening. If this disassembly and loss of integrity can be slowed down, we will be able to create fruit that can be picked vine-ripe and still withstand current commercial handling practices. Previous research showed a dramatic loss of galactose (a sugar cell wall component) occurred from the wall during ripening. We suspect this loss may play a role in softening. The present study reports on the effect of ethylene on the expression of three of seven genes we have identified in tomato, possibly involved in degrading the fruit cell wall. Ethylene, which is often called the "ripening hormone", may regulate the turning-on of these genes during the ripening process. Our results showed that ethylene turned some genes on and others off, suggesting a multi-function role for these genes during fruit ontogeny. It also confirms ideas we had about some fruit softening being independent of ripening. Such information will lead to our ability to allow tomato fruit to ripen normally while slowing down the softening process, leading to increased quality and shelf-life. This will benefit consumers, packers and shippers by increasing the shelf-life of fruit while maintaining their quality.

Technical Abstract: Recent studies indicate that beta-galactosidases play an important role in fruit development and ripening. The temporal mRNA expression patterns of a recently discovered family of tomato beta-galactosidase (TBG) genes suggest that some of these genes may be regulated by ethylene, but direct evidence for this has been lacking. Because of the dramatic changes in mRNA expression patterns that some of these genes exhibit at the onset of fruit ripening (when autocatalytic ethylene production begins), we analyzed the effects of ethylene in TBG4, TBG5 and TBG6, as well as their interactions with other ripening-related genes. We analyzed the expression patterns of these TBG genes in wild type and three tomato ripening-impaired mutants: rin, nor and Nr. Northern blot analysis showed that ethylene increased the accumulation of TBG-4 mRNA up to 20-fold, except in the nor mutant. Conversely, ethylene decreased mRNA expression of both TBG-5 and TBG-6 in wild type and mutant fruit, although each at different levels. We present a model for the possible influence of the rin, nor and Nr genes on the mRNA abundance of TBG genes, and in relation with the climacteric production of ethylene in tomato fruit.