Adventitious root formation of in vitro peach shoots is regulated by auxin and ethylene

Adventitious root formation is a critical step in micropropagation and genetic transformation. However, it is often a limiting factor for some crop species, particularly woody plants. In this report, we studied adventitious rooting using in vitro shoots of peach, a fruit tree species that is notoriously recalcitrant to genetic transformation and adventitious root induction. We found that culture age affected adventitious rooting efficiency. Hormone analysis revealed that the peach shoots maintained in vitro for 2 years (yr) with a higher rooting rate contained more endogenous indole-3-acetic acid (IAA) than those grown in vitro for 1yr under the same growth conditions. Treatment: of peach shoots with Arninoethoxyvinylglycine (AVG), a potent auxin biosynthesis inhibitor, inhibited adventitious rooting. To explore the association of gene expression with adventitious rooting, we performed a comparative transcriptome analysis. We found that genes encoding key enzymes in auxin biosynthesis were up-regulated in 2yr shoots. In contrast, genes involved in ethylene biosynthesis and its signaling pathway were down-regulated in 2yr shoots. Addition of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate metabolic precursor of ethylene, significantly inhibited adventitious rooting in a dose-dependent manner. Therefore, auxin and ethylene act antagonistically on adventitious rooting. Taken together, our results shed new insights into the mechanism regulating adventitious rooting of peach shoots, and may help develop novel rooting methods for peach and related woody plants.