PbHCT4 regulates growth through affecting chlorogenic acid (CGA) content in pear

Due to its many advantages, dwarfing and dense planting is an important mode of modern fruit tree cultivation. Phenols have been reported to play various roles in the growth regulation of plants. Here, to verify the correlation between chlorogenic acid (CGA) and the growth of pear trees, the CGA content of standard and dwarf pear trees as well as the effect of exogenous CGA upon their growth, were investigated and analyzed. Our results showed that the CGA content of two dwarf-type varieties, ‘Zhongai 1′ (Z1) and ‘PY-9′ was significantly higher than that of two standard-type Pyrus betulaefolia (P1 and P2). Whereas a low concentration of CGA accelerated pear tree growth, and a high concentration of CGA could inhibit it. Then, through an expression pattern analysis of four CGA synthesis-related genes, PbHCT1–4, we found that the dwarf phenotype might be related to the expression levels of PbHCTs, especially to those of PbHCT2–4 in shoots. Of these, PbHCT4 was selected as a candidate gene and transformed into tobacco. When compared with control tobacco plants, the transgenic plants attained taller heights and had a greater CGA content, as well as increased expression levels of the auxin efflux carrier gene, NbPIN. Accordingly, we speculate the PbHCT4 gene promotes the synthesis of CGA, which influences plant growth by mediating auxin's transport in pear trees. These findings are helpful for advancing analysis of dwarf mechanism, which is critical for the breeding of new dwarf pear varieties.