PLANT PHYSIOLOGY , Vol 113, Issue 3 707-718, Copyright © 1997 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Differential Expression and Turnover of the Tomato Polyphenol Oxidase Gene Family during Vegetative and Reproductive Development
P. Thipyapong, D. M. Joel and J. C. Steffens
Department of Plant Breeding and Biometry, 252 Emerson Hall, Cornell University, Ithaca, New York 14853-1901 (P.T., J.C.S.)
Polyphenol oxidases (PPOs) are encoded by a highly conserved, seven-member
gene family clustered within a 165-kb locus on chromosome 8 of tomato
(Lycopersicon esculentum). Using gene-specific probes capable of
differentiating between PPO A/C, PPO B, PPO D, and PPO E/F, we examined the
spatial and temporal expression of this gene family during vegetative and
reproductive development. RNA blots and in situ hybridization using these
probes showed that although PPO expression is primarily confined to early
stages of development, the steady-state mRNA levels of these genes are
subject to complex patterns of spatial and temporal regulation in
vegetative and reproductive organs. Young tomato leaves and flowers possess
the most abundant PPO transcripts. PPO B is the most abundant in young
leaves, whereas in the inflorescence PPO B and E/F transcripts are
dominant. Differential expression of PPOs is also observed in various
trichome types. PPO A/C are specifically expressed in type I and type IV
trichomes. In contrast, PPO D is only expressed in type VI trichomes. Type
I, IV, and VI trichomes possess PPO E/F transcripts. Immunolocalization
verified the translational activity of PPOs identified by in situ
hybridization and suggested cell-type-specific, developmentally programmed
PPO turnover. In addition, immunolocalization demonstrated the accumulation
of PPO in specific idioblast cells of stems, leaves, and fruits.
