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The Plant Cell, Vol. 26: 585–601, February 2014, www.plantcell.org ã 2014 American Society of Plant Biologists. All rights reserved.
Tomato GOLDEN2-LIKE Transcription Factors Reveal
Molecular Gradients That Function during Fruit
Development and Ripening
W OPEN
Cuong V. Nguyen,a,b Julia T. Vrebalov,b Nigel E. Gapper,b Yi Zheng,b Silin Zhong,b,c Zhangjun Fei,b,d
and James J. Giovannonib,d,1
a Department
of Plant Breeding and Genetics, Cornell University, Ithaca, New York 14853
Thompson Institute for Plant Research, Ithaca, New York 14853
c School of Life Sciences, Chinese University of Hong Kong, Sha Tin, Hong Kong
d U.S. Department of Agriculture/Agriculture Research Service, Robert W. Holley Centre for Agriculture and Health, Ithaca, New York
14853
b Boyce
Fruit ripening is the summation of changes rendering fleshy fruit tissues attractive and palatable to seed dispersing
organisms. For example, sugar content is influenced by plastid numbers and photosynthetic activity in unripe fruit and later by
starch and sugar catabolism during ripening. Tomato fruit are sinks of photosynthate, yet unripe green fruit contribute
significantly to the sugars that ultimately accumulate in the ripe fruit. Plastid numbers and chlorophyll content are influenced
by numerous environmental and genetic factors and are positively correlated with photosynthesis and photosynthate
accumulation. GOLDEN2-LIKE (GLK) transcription factors regulate plastid and chlorophyll levels. Tomato (Solanum
lycopersicum), like most plants, contains two GLKs (i.e., GLK1 and GLK2/UNIFORM). Mutant and transgene analysis
demonstrated that these genes encode functionally similar peptides, though differential expression renders GLK1 more
important in leaves, while GLK2 is predominant in fruit. A latitudinal gradient of GLK2 expression influences the typical uneven
coloration of green and ripe wild-type fruit. Transcriptome profiling revealed a broader fruit gene expression gradient...