Abstract
Sepal is an important component of the tomato flower and fruit that typically protects the flower in bud and functions as a support for petals and fruits. Moreover, sepal appearance influences the commercial property of tomato nowadays. However, the phenotype information and development mechanism of the natural variation of sepal morphology in the tomato is still largely unexplored. To study the developmental mechanism and to determine key genes related to downward sepal in the tomato, we compared the transcriptomes of sepals between downward sepal (dsp) mutation and the wild-type by RNA sequencing and found that the differentially expressed genes were dominantly related to cell expansion, auxin, gibberellins and cytokinin. dsp mutation affected cell size and auxin, and gibberellins and cytokinin contents in sepals. The results showed that cell enlargement or abnormal cell expansion in the adaxial part of sepals in dsp. As reported, auxin, gibberellins and cytokinin were important factors for cell expansion. Hence, dsp mutation regulated cell expansion to control sepal morphology, and auxin, gibberellins and cytokinin may mediate this process. One ARF gene and nine SAUR genes were dramatically upregulated in the sepal of the dsp mutant, whereas seven AUX/IAA genes were significantly downregulated in the sepal of dsp mutant. Further bioinformatic analyses implied that seven AUX/IAA genes might function as negative regulators, while one ARF gene and nine SAUR genes might serve as positive regulators of auxin signal transduction, thereby contributing to cell expansion in dsp sepal. Thus, our data suggest that 17 auxin-responsive genes are involved in downward sepal formation in the tomato. This study provides valuable information for dissecting the molecular mechanism of sepal morphology control in the tomato.
Highlights
The tomato (Solanum lycopersicum L.) is an important commercial crop and model for studying the floral organ development of angiosperms
The WT tomato plant was characterized by typical flat-spread sepals, the dsp mutant, which was generated through natural mutation, exhibited an unusual “downward sepal” phenotype (Figure 1a)
Dsp promoted downward sepals through the regulation of adaxial cell size in sepals, and this process might be mediated by auxin, cytokinin and gibberellin
Summary
The tomato (Solanum lycopersicum L.) is an important commercial crop and model for studying the floral organ development of angiosperms. Tomato sepals are persistently protect young fruits and improve the quality of the appearance of mature fruits. As living standards increase, many people started to consider the quality and appearance of tomato sepals. Healthy and flat sepals have become an important standard for measuring the quality of tomato fruits, enhancing visual esthetics and reflecting fruit freshness. The morphology and size of the sepals have been associated with the yield and quality of the fruit. The larger sepal size tightly associates with the protection of flower whorl and better fruit quality [1]. In SlMBP21-RNAi tomato, the sepals are longer and fruit sets are improved [2]. Sepal morphology is closely associated with fruit development
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