Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2001
Publication Date: 9/1/2001
Citation: BARRY, C., FOX, E., YEN, H., LEE, S., YING, T., GRIERSON, D., GIOVANNONI, J.J. ANALYSIS OF THE ETHYLENE RESPONSE IN THE EPINASTIC (EPI) MUTANT OF TOMATO. PLANT PHYSIOLOGY. 2001. V. 127. P. 58-66. Interpretive Summary: Ethylene is a gaseous plant hormone that impacts numerous aspects of crop growth and resulting product quality including fruit ripening, senescence, abscission, susceptibility to pathogen infection, plant growth and elongation responses, and shelflife. The ability to control ethylene biosynthesis and/or perception will facilitate production of higher quality ycrops and crop products with reduced spoilage. We are investigating the molecular mechanism by which plants perceive and respond to ethylene as a path to improved crop quality. The characteristics of the tomato epinastic (epi) mutant are suggestive of a lesion in a gene involved in ethylene signal transduction and thus the corresponding gene may represent a molecular tool for manipulating ethylene responses in plants. Specifically, the epi mutant behaves as though it is constantly being exposed to ethylene. In this study we created double mutants harboring the eepi mutation in combination with an ethylene receptor mutation (no ethylen response) to determine what aspects of ethylene response are in fact controlled by the epi gene. Our results indicated that the epi gene regulates a subset of ethylene responses specific to cell growth and elongation with little effect on ripening and senescence characteristics.
Technical Abstract: Ethylene can alter plant morphology due to its effect on cell expansion. The most widely documented example of ethylene mediated cell expansion is promotion of the 'triple response' of seedlings grown in the dark in ethylene. The constitutive triple response (ctr1) mutant of Arabidopsis lies within the ethylene-response pathway and was identified based upon a constitutive ethylene response phenotype in the absence of ethylene. The epinastic (epi) mutant of tomato possesses a similar seedling phenotype to ctr1. Additionally, in adult plants both the leaves and the petioles display epinastic curvature. These phenotypes are suggestive of a constitutive response to ethylene. We have analyzed the ethylene response of epi at the morphological and molecular level with the aid of a double mutant (epi/epi;Nr/Nr) homozygous for both the recessive epi and dominant ethylene-insensitive Never-ripe (Nr) loci. We show that epidermal cellular rmorphology is altered in epi with cells showing a more rounded swollen phenotype than wild type cells. The epi locus has also been placed on the tomato RFLP map on the long arm of chromosome 4 and does not demonstrate linkage to reported tomato CTR1 homologs. Finally, double mutant analyses indicate that epi does not possess a global constitutive ethylene response but may either directly affect a subset of responses or alter vegetative growth and development which in turn activates the ethylene-response pathway.