Abstract
Color is an important agronomic trait of pears, and the anthocyanin content of fruit is immensely significant for pear coloring. In this study, an anthocyanin-activating R2R3-MYB transcription factor gene, PyMYB10.1, was isolated from fruits of red sand pear (Pyrus pyrifolia cv. Aoguan). Alignments of the nucleotide and amino acid sequences suggested that PyMYB10.1 was involved in anthocyanin regulation. Similar to PyMYB10, PyMYB10.1 was predominantly expressed in red tissues, including the skin, leaf and flower, but it was minimally expressed in non-red fruit flesh. The expression of this gene could be induced by light. Dual-luciferase assays indicated that both PyMYB10 and PyMYB10.1 activated the AtDFR promoter. The activation of AtDFR increased to a greater extent when combined with a bHLH co-factor, such as PybHLH, MrbHLH1, MrbHLH2, or AtbHLH2. However, the response of this activation depended on the protein complex formed. PyMYB10-AtbHLH2 activated the AtDFR promoter to a greater extent than other combinations of proteins. PyMYB10-AtbHLH2 also induced the highest anthocyanin accumulation in tobacco transient-expression assays. Moreover, PybHLH interacted with PyMYB10 and PyMYB10.1. These results suggest that both PyMYB10 and PyMYB10.1 are positive anthocyanin biosynthesis regulators in pears that act via the formation of a ternary complex with PybHLH. The functional characterization of PyMYB10 and PyMYB10.1 will aid further understanding of the anthocyanin regulation in pears.
Highlights
Pear is an economically important temperate fruit
At least 22 primary species of Pyrus have been identified; only the four major species Pyrus bretschneideri, Pyrus pyrifolia, Pyrus ussuriensis, and Pyrus communis have been utilized for commercial fruit production [1].The sand pear (P. pyrifolia)is primarily cultivated in eastern Asia
PyMYB10.1 is phylogenetically close to the known anthocyanin MYBI type regulators, those from Rosaceae, but is more distantly related to the Arabidopsis AtTT2 [32], which controls proanthocyanidin synthesis; Arabidopsis AtMYB11 and AtMYB12 [33], which control flavonol synthesis; and FaMYB1 from strawberries [15], which represses anthocyanin synthesis (Fig 2)
Summary
Pear is an economically important temperate fruit. At least 22 primary species of Pyrus have been identified; only the four major species Pyrus bretschneideri, Pyrus pyrifolia, Pyrus ussuriensis, and Pyrus communis have been utilized for commercial fruit production [1].The sand pear (P. pyrifolia)is primarily cultivated in eastern Asia. The sand pear can be divided into four types based on skin color: red, green, russet, and an intermediate color (russet and green). Most cultivated sand pear varieties are green and russet. Their supply is inadequate [2].red color has recently become an important breeding objective for pear cultivars, especially in Asian countries such as China.
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