Multiple tissue-specific expression of rice seed-shattering gene SH4 regulated by its promoter pSH4

Rice seed shattering is an important domestication syndrome encoded by a gene named as SH4. The coding region of SH4 has been well studied regarding its function and roles in evolution. However, its promoter has not been identified, which limited our understanding of the detailed regulatory mechanisms of this gene. It is therefore critical to characterize the promoter and study its expression pattern.

We analyzed the 5' upstream sequences of this gene and identified a ~2.6 kb fragment with typical promoter features, which was designated as pSH4. The promoter contained a number of cis-acting elements related to abscisic acid (ABA) and a CpG island that were characteristics of multiple tissue-specific expression. We isolated and ligated pSH4 to the β-glucuronidase (GUS) reporter gene, and transformed it into a japonica rice cultivar to determine the multiple expression pattern of SH4. Histochemical location and fluorescence analyses of GUS activity of transgenic plants indicated multiple tissue-specific expression of pSH4 in the seed-pedicel junction region of mature panicles (with highest level), stems, coleoptiles of germinated seeds, and scutella of mature seeds.

The multiple tissue-specific expression pSH4 is categorized as a spatiotemporal promoter that drives the expression of the SH4 gene in different rice tissues, in addition to the seed-pedicel junction region. Our findings suggest that SH4 may have additional functions in the growth and development of rice, apart from its major role in seed shattering.