TOMATO AGAMOUS-LIKE 1 is a component of the fruit ripening regulatory network.
After fertilization, the expanding carpel of fleshy fruit goes through a phase change to ripening. Although the role of ethylene signalling in mediating climacteric ripening has been established, knowledge regarding the regulation of ethylene biosynthesis and its association with fruit developmental programs is still lacking. A functional screen of tomato transcription factors showed that silencing of the TOMATO AGAMOUS-LIKE 1 (TAGL1) MADS box gene results in altered fruit pigmentation. Over-expressing TAGL1 as a chimeric repressor suggested a role in controlling ripening, as transgenic tomato fruit showed reduced carotenoid and ethylene levels, suppressed chlorophyll breakdown, and down-regulation of ripening-associated genes. Moreover, fruits over-expressing TAGL1 accumulated more lycopene, and their sepals were swollen, accumulated high levels of the yellow flavonoid naringenin chalcone and contained lycopene. Transient promoter-binding assays indicated that part of the TAGL1 activity in ripening is executed through direct activation of ACS2, an ethylene biosynthesis gene that has recently been reported to be a target of the RIN MADS box factor. Examination of the TAGL1 transcript and its over-expression in the rin mutant background suggested that RIN does not regulate TAGL1 or vice versa. The results also indicated RIN-dependent and -independent processes that are regulated by TAGL1. We also noted that fruit of TAGL1 loss-of-function lines had a thin pericarp layer, indicating an additional role for TAGL1 in carpel expansion prior to ripening. The results add a new component to the current model of the regulatory network that controls fleshy fruit ripening and its association with the ethylene biosynthesis pathway.
Itkin
Maxim
M
Department of Plant Sciences, Weizmann Institute of Science, PO Box 26, Rehovot 76100, Israel.
Seybold
Heike
H
Breitel
Dario
D
Rogachev
Ilana
I
Meir
Sagit
S
Aharoni
Asaph
A
D002338:Carotenoids / Q000096:biosynthesis; D019295:Computational Biology; D005030:Ethylenes / Q000096:biosynthesis; D005638:Fruit / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D000077276:Lycopene; D018551:Solanum lycopersicum / Q000235:genetics* / Q000378:metabolism; D026161:MADS Domain Proteins / Q000235:genetics / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D010858:Pigmentation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics
D005030:Ethylenes; D026161:MADS Domain Proteins; D010940:Plant Proteins; D018749:RNA, Plant; D002338:Carotenoids; C036216:ethylene; D000077276:Lycopene