Characterization of <i>RIN</i> Isoforms and Their Expression in Tomato Fruit Ripening

• Main Authors: Maria A. Slugina, Gleb I. Efremov, Anna V. Shchennikova, Elena Z. Kochieva
• Format: Article
• Language: English
• Published: MDPI AG 2021-07-01
• Series: Cells
• Subjects: tomato <i>Solanum lycopersicum</i> L.; wild green-fruited tomato species; MADS-RIN; fruit ripening; gene structure; splicing
• Online Access: https://www.mdpi.com/2073-4409/10/7/1739

Ripening of tomato fleshy fruit is coordinated by transcription factor RIN, which triggers ethylene and carotenoid biosynthesis, sugar accumulation, and cell wall modifications. In this study, we identified and characterized complete sequences of the <i>RIN</i> chromosomal locus in two tomato <i>Solanum lycopersicum</i> cultivars, its <i>rin/RIN</i> genotype, and three wild green-fruited species differing in fruit color and composition. The results reveal that <i>S</i>. <i>lycopersicum</i> cultivars and some wild species (<i>S. pennellii</i>, <i>S. habrochaites</i>, and <i>S. huaylasense</i>) had a 3′-splicing site enabling the transcription of <i>RIN1i</i> and <i>RIN2i</i> isoforms. The other wild species (<i>S. arcanum</i>, <i>S. chmielewskii</i>, <i>S. neorickii</i>, and <i>S. peruvianum</i>) had a 3′-splicing site only for <i>RIN2i</i>, which was consistent with <i>RIN1i</i> and <i>RIN2i</i> expression patterns. The genotype <i>rin</i>/<i>RIN</i>, which had an extended 3′-terminal deletion in the <i>rin</i> allele, mainly expressed the chimeric <i>RIN–MC</i> transcript, which was also found in cultivars (<i>RIN</i>/<i>RIN</i>). The RIN1, but not RIN2, protein is able to induce the transcription of the reporter gene in the Y2H system, which positively correlated with the transcription profile of <i>RIN1i</i> and RIN target genes. We suggest that during fruit ripening, RIN1 activates ripening-related genes, whereas RIN2 and RIN–MC act as modulators by competing for RIN-binding sites in gene promoters, which should be confirmed by further studies on the association between <i>RIN</i>-splicing mechanisms and tomato fruit ripening.