Overexpression of Prunus DAM6 inhibits growth, represses bud break competency of dormant buds and delays bud outgrowth in apple plants.

Hisayo Yamane,Takakazu Matsuura,Masato Wada,Takashi Hirayama,Yutaro Osako,Mikiko Kojima,Chikako Honda,Yoko Ikeda,Hitoshi Sakakibara,Ryutaro Tao,Mei Gao-Takai,Haibing Yang

doi:10.1371/journal.pone.0214788

Abstract

Most deciduous fruit trees cultivated in the temperate zone require a genotype-dependent amounts of chilling exposure for dormancy release and bud break. In Japanese apricot (Prunus mume), DORMANCY-ASSOCIATED MADS-box 6 (PmDAM6) may influence chilling-mediated dormancy release and bud break. In this study, we attempted to elucidate the biological functions of PmDAM6 related to dormancy regulation by analyzing PmDAM6-overexpressing transgenic apple (Malus spp.). We generated 35S:PmDAM6 lines and chemically inducible overexpression lines, 35S:PmDAM6-GR. In both overexpression lines, shoot growth was inhibited and early bud set was observed. In addition, PmDAM6 expression repressed bud break competency during dormancy and delayed bud break. Moreover, PmDAM6 expression increased abscisic acid levels and decreased cytokinins contents during the late dormancy and bud break stages in both 35S:PmDAM6 and 35S:PmDAM6-GR. Our analysis also suggested that abscisic acid levels increased during dormancy but subsequently decreased during dormancy release whereas cytokinins contents increased during the bud break stage in dormant Japanese apricot buds. We previously revealed that PmDAM6 expression is continuously down-regulated during dormancy release toward bud break in Japanese apricot. The PmDAM6 expression pattern was concurrent with a decrease and increase in the abscisic acid and cytokinins contents, respectively, in dormant Japanese apricot buds. Therefore, we hypothesize that PmDAM6 represses the bud break competency during dormancy and bud break stages in Japanese apricot by modulating abscisic acid and cytokinins accumulation in dormant buds.

Highlights

Perennial woody plants in temperate zones synchronize their annual growth patterns with seasonal environmental changes
When 35S:PmDAM6 and WT plants were exposed to a cool conditions (10 ̊C), leaf shedding was observed at around the same time
To investigate the role of PmDAM6 in dormancy regulation, we used apple, a relative of Japanese apricot, both belonging to Rosaceae, because there are transformable apple accessions [38]

Summary

Introduction

Perennial woody plants in temperate zones synchronize their annual growth patterns with seasonal environmental changes. Discriminating between paradormancy and endodormancy, and endodormancy and ecodormancy, is problematic for fruit tree species of the genus Prunus, such as peach (P. persica) and Japanese apricot (P. mume), in which lateral flower and leaf buds are often used for dormancy research. In these fruit tree species, whether buds are paradormant, endodormant or ecodormant has been estimated according to the competency of bud break, which is often based on the mean time to bud break or bud break percentage in forcing condition [4, 6, 7, 8, 9]. Without the experiments such as incubating branch or single node cuttings in forcing condition, we cannot precisely distinguish paradormancy, endodormancy and ecodormancy in field trees

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