Transcriptome Analysis Reveals Multiple Hormones, Wounding and Sugar Signaling Pathways Mediate Adventitious Root Formation in Apple Rootstock.

Ke Li,Yuan Meng,Zhen Liu,Lu Bao,Mingyu Han,Feng Dong,Dong Zhang,Caiping Zhao,Jiangping Mao,Libo Xing,Yongqi Liang

doi:10.3390/ijms19082201

Abstract

Adventitious roots (AR) play an important role in the vegetative propagation of apple rootstocks. The potential role of hormone, wounding, and sugar signalling pathways in mediating AR formation has not been adequately explored and the whole co-expression network in AR formation has not been well established in apple. In order to identify the molecular mechanisms underlying AR formation in ‘T337’ apple rootstocks, transcriptomic changes that occur during four stages of AR formation (0, 3, 9 and 16 days) were analyzed using high-throughput sequencing. A total of 4294 differentially expressed genes were identified. Approximately 446 genes related to hormones, wounding, sugar signaling, root development, and cell cycle induction pathways were subsequently selected based on their potential to be involved in AR formation. RT-qPCR validation of 47 genes with known functions exhibited a strong positive correlation with the RNA-seq data. Interestingly, most of the candidate genes involved in AR formation that were identified by transcriptomic sequencing showed auxin-responsive expression patterns in an exogenous Indole-3-butyric acid (IBA)-treatment assay: Indicating that endogenous and exogenous auxin plays key roles in regulating AR formation via similar signalling pathways to some extent. In general, AR formation in apple rootstocks is a complex biological process which is mainly influenced by the auxin signaling pathway. In addition, multiple hormones-, wounding- and sugar-signaling pathways interact with the auxin signaling pathway and mediate AR formation in apple rootstocks.

Highlights

Apple (Malus domestica Borkh.) is one of the most commercially important fruits in the world
Stage 1 (S1) represents stem cuttings treated with 1 mg·L−1 indole-3-butyric acid (IBA) at 0 day (0 day, competent cells); stage 2 (S2) represents stem cuttings in which Adventitious root (AR) formation was induced at 3 day (3 day, Cell cycle reactivation); stage 3 (S3) represents stem cuttings in which callus formed at the base of the stem at 9 day (9 day, Activation of AR primordium formation); and stage 4 (S4) represents stem cuttings in which AR broke through the epidermis and AR emerged at 16 day (16 day, AR outgrowth)
The current study proposes a preliminary model which describes the important biological processes occurring during AR formation in apple rootstocks

Summary

Introduction

Apple (Malus domestica Borkh.) is one of the most commercially important fruits in the world. In terms of nutritional value and economic importance, apple, grape, orange, and banana are the most predominant fruit crops globally. Among these four fruit crops, apple is the most widely consumed and China is the world’s largest apple producer. The ‘T337’ dwarfing apple rootstock is widely used and confers early fruiting and high yields. Adventitious root (AR) formation, represents a limiting factor in the vegetative propagation of apple rootstocks and other tree species. The molecular mechanisms underlying adventitious rooting are still not completely understood. The study of the molecular regulatory mechanisms involved in AR formation in ‘T337’ apple rootstock is important for understanding and solving the problems associated with AR development

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Discussion

Conclusion