The RIN-MC Fusion of MADS-Box Transcription Factors Has Transcriptional Activity and Modulates Expression of Many Ripening Genes

Abstract

Fruit development and ripening is regulated by genetic and environmental factors and is of critical importance for seed dispersal, reproduction, and fruit quality. Tomato () () mutant fruit have a classic ripening-inhibited phenotype, which is attributed to a genomic DNA deletion resulting in the fusion of two truncated transcription factors, and In wild-type fruit, RIN, a MADS-box transcription factor, is a key regulator of the ripening gene expression network, with hundreds of gene targets controlling changes in color, flavor, texture, and taste during tomato fruit ripening; , on the other hand, has low expression in fruit, and the potential functions of the fusion gene in ripening remain unclear. Here, overexpression of in transgenic wild-type cv Ailsa Craig tomato fruits impaired several ripening processes, and down-regulating expression in the mutant was found to stimulate the normal yellow mutant fruit to produce a weak red color, suggesting a distinct negative role for in tomato fruit ripening. By comparative transcriptome analysis of and:: RNA interference fruits, a total of 1,168 and 1,234 genes were identified as potential targets of RIN-MC activation and inhibition. Furthermore, the fusion gene was shown to be translated into a chimeric transcription factor that was localized to the nucleus and was capable of protein interactions with other MADS-box factors. These results indicated that tomato RIN-MC fusion plays a negative role in ripening and encodes a chimeric transcription factor that modulates the expression of many ripening genes, thereby contributing to the mutant phenotype.

A critical evaluation of the role of ethylene and MADS transcription factors in the network controlling fleshy fruit ripening

“…Research by Li et al . () and Ito et al . () showed the mutated RIN‐MC is actually a gain‐of‐function mutation.…”

“…Tissue samples were selected from: *Li et al . () at BK+5 stage; **Fujisawa et al . () at Pink stage; and ***Zhong et al .…”

“…Additionally, the hybrid RIN‐MC protein accumulates in the nucleus, is capable of interacting with other MADS proteins (Li et al ., ) and controls the expression of many genes. A further feature of the RIN‐MC chimeric protein, which may explain its effect, is that it appears to have a repressor function (Ito et al ., ; Li et al ., ).…”

“…(e) Expression of MADS ‐ RIN was analyzed at various ripening stages in WT and rin fruit (reproduced with permission from Fig. (b) in Li et al ., ), using primer pair 1 and pair 2. In the rin mutant, truncated MADS ‐ RIN is fused to truncated MADS ‐ MC forming RIN ‐ MC transcript, which accumulates to high levels in ripe fruits at mature green ( MG ), breaker ( BK ), and PINK / YELLOW and red‐ripe ( RR )/yellowripe ( YR ) stages, compared to normal MADS ‐ RIN and MADS ‐ MC in WT AC (primer pairs 1 and 2 are specific to truncated MADS ‐ RIN or MADS ‐ MC in the RIN ‐ MC fusion gene in the rin mutant).…”

“…() concluded that fruit ripening could initiate without MADS‐RIN, whereas Li et al . () proposed that downregulation of RIN expression inhibited initiation and development of ripening.…”