Histone Acetylation at the Promoter for the Transcription Factor PuWRKY31 Affects Sucrose Accumulation in Pear Fruit.

Sugar content is an important trait of fleshy fruit, and elevating sucrose levels is a major goal in horticultural crop breeding. Here, we examined the sugar content in two varieties of the Ussurian pear (Pyrus ussuriensis), Nanguo (NG) and its bud sport (BNG), and we found that sucrose content was higher in BNG fruit than in NG fruit. We compared the transcriptomes of the two varieties using RNA-seq and identified a SWEET (Sugars Will Eventually be Exported Transporter) gene, PuSWEET15, expressed at higher levels in BNG fruit. Heterologous expression of PuSWEET15 in a SUSY7/ura yeast (Saccharomyces cerevisiae) strain showed that PuSWEET15 is an active sucrose transporter. Overexpression of PuSWEET15 in NG pear fruit increased sucrose content, while silencing of PuSWEET15 in BNG fruit decreased sucrose content. The WRKY transcription factor PuWRKY31 was also expressed more highly in BNG fruit than in NG fruit, and we found that PuWRKY31 bound to the PuSWEET15 promoter and induced its transcription. The histone acetylation level of the PuWRKY31 promoter was higher in BNG fruit, suggesting a mechanism by which sucrose levels can be elevated.