EARLY BUD BREAK 1 triggers bud break in peach trees by regulating hormone metabolism, the cell cycle, and cell wall modifications.

In a previous study we identified EARLY BUD BREAK 1 (EBB1), an ERF transcription factor, in peach (Prunus persica var. nectarina cultivar Zhongyou 4); however, little is known of how PpEBB1 may regulate bud break. To verify the function of PpEBB1 in bud break, PpEBB1 was transiently transformed into peach buds, resulting in early bud break. Bud break occurred earlier in PpEBB1-oe poplar (Populus trichocarpa) obtained by heterologous transformation than in wild type (WT), consistent with the peach bud results, indicating that PpEBB1 can promote bud break. To explore how PpEBB1 affects bud break, differentially expressed genes (DEGs) between WT and PpEBB1-oe poplar plants were identified by RNA-sequencing. The expression of DEGs associated with hormone metabolism, cell cycle, and cell wall modifications changed substantially according to qRT-PCR. Auxin, ABA, and total trans-zeatin-type cytokinin levels were higher in the PpEBB1-oe plants than in WT plants, while the total N6-(Δ 2-isopentenyl)-adenine-type cytokinins was lower. Yeast two-hybrid and bimolecular fluorescence complementation assays verified that a cell wall modification-related protein (PpEXBL1) interacted with PpEBB1 suggesting that PpEBB1 could interact with these cell wall modification proteins directly. Overall, our study proposed a multifaceted explanation for how PpEBB1 regulates bud break and showed that PpEBB1 promotes bud break by regulating hormone metabolism, the cell cycle, and cell wall modifications.

Overexpression of the Peach Transcription Factor Early Bud-Break 1 Leads to More Branches in Poplar.

Shoot branching is an important adaptive trait that determines plant architecture. In a previous study, the Early bud-break 1 (EBB1) gene in peach (Prunus persica var. nectarina) cultivar Zhongyou 4 was transformed into poplar (Populus trichocarpa). PpEBB1-oe poplar showed a more branched phenotype. To understand the potential mechanisms underlying the EBB1-mediated branching, transcriptomic and proteomics analyses were used. The results showed that a large number of differentially expressed genes (DEGs)/differentially expressed proteins (DEPs) associated with light response, sugars, brassinosteroids (BR), and nitrogen metabolism were significantly enriched in PpEBB1-oe poplar. In addition, contents of sugars, BR, and amino acids were measured. Results showed that PpEBB1 significantly promoted the accumulation of fructose, glucose, sucrose, trehalose, and starch. Contents of brassinolide (BL), castasterone (CS), and 6-deoxocathasterone (6-deoxoCS) were all significantly changed with overexpressing PpEBB1. Various types of amino acids were measured and four of them were significantly improved in PpEBB1-oe poplar, including aspartic acid (Asp), arginine (Arg), cysteine (Cys), and tryptohpan (Trp). Taken together, shoot branching is a process controlled by a complex regulatory network, and PpEBB1 may play important roles in this process through the coordinating multiple metabolic pathways involved in shoot branching, including light response, phytohormones, sugars, and nitrogen.

PpEBB1 directly binds to the GCC box-like element of auxin biosynthesis related genes.

EARLY BUD-BREAK 1 (EBB1) can promote bud break, and this function is likely conserved in woody plants. To get a more comprehensive understand of its function, peach (Prunus persica var. nectarina cultivar Zhongyou 4) PpEBB1 was overexpressed in Arabidopsis; the resultant phenotypes, including curved leaves, abnormal development of floral organs and low seed set, were similar to those of DORNRÖSCHEN-LIKE (DRNL) overexpression, indicating that PpEBB1 was a putative ortholog of AtDRNL. PpEBB1 bound to the GCC box-like element in the STYLISH1/SHI RELATED SEQUENCE5 (STY1/SRS5) promoter of peach, which has been proposed to occur in Arabidopsis as well. A GCC box-like element was also found in the YUCCA1 (YUC1) promoter, and PpEBB1 could bind to this element and activate the expression of YUC1. In addition to the elevated auxin content in the PpEBB1-oe plants as observed in our previous study, these results suggest that PpEBB1 can regulate auxin biosynthesis by directly activating related genes. Besides, we screened a zinc finger RING-finger protein, MYB30-INTERACTING E3 LIGASE 1 (PpMIEL1), showing interaction with PpEBB1, suggesting that the stability of PpEBB1 might be influenced by PpMIEL1 through ubiquitination.