Comparative genomics reveals candidate carotenoid pathway regulators of ripening watermelon fruit.
BACKGROUND
Many fruits, including watermelon, are proficient in carotenoid accumulation during ripening. While most genes encoding steps in the carotenoid biosynthetic pathway have been cloned, few transcriptional regulators of these genes have been defined to date. Here we describe the identification of a set of putative carotenoid-related transcription factors resulting from fresh watermelon carotenoid and transcriptome analysis during fruit development and ripening. Our goal is to both clarify the expression profiles of carotenoid pathway genes and to identify candidate regulators and molecular targets for crop improvement.


RESULTS
Total carotenoids progressively increased during fruit ripening up to ~55 μg g(-1) fw in red-ripe fruits. Trans-lycopene was the carotenoid that contributed most to this increase. Many of the genes related to carotenoid metabolism displayed changing expression levels during fruit ripening generating a metabolic flux toward carotenoid synthesis. Constitutive low expression of lycopene cyclase genes resulted in lycopene accumulation. RNA-seq expression profiling of watermelon fruit development yielded a set of transcription factors whose expression was correlated with ripening and carotenoid accumulation. Nineteen putative transcription factor genes from watermelon and homologous to tomato carotenoid-associated genes were identified. Among these, six were differentially expressed in the flesh of both species during fruit development and ripening.


CONCLUSIONS
Taken together the data suggest that, while the regulation of a common set of metabolic genes likely influences carotenoid synthesis and accumulation in watermelon and tomato fruits during development and ripening, specific and limiting regulators may differ between climacteric and non-climacteric fruits, possibly related to their differential susceptibility to and use of ethylene during ripening.
Stefania
S
Grassi
Gabriella
G
Piro
Je Min
JM
Lee
Yi
Y
Zheng
Zhangjun
Z
Fei
Giuseppe
G
Dalessandro
James J
JJ
Giovannoni
Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali (Di,S,Te,B,A,), Università del Salento, via Prov,le Lecce-Monteroni,73100 Lecce, Italy. marcello.lenucci@unisalento.it.
Marcello S
MS
Lenucci
D002338:Carotenoids / Q000235:genetics* / Q000378:metabolism; D029773:Citrullus / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D005030:Ethylenes / Q000494:pharmacology; D005638:Fruit / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D000077276:Lycopene; D053858:Metabolic Networks and Pathways / Q000187:drug effects / Q000235:genetics*; D010940:Plant Proteins / Q000096:biosynthesis; D030821:Plants, Genetically Modified
D005030:Ethylenes; D010940:Plant Proteins; D002338:Carotenoids; C036216:ethylene; D000077276:Lycopene