Abstract
Adventitious root (AR) formation is a bottleneck for the mass propagation of apple rootstocks, and water stress severely restricts it. Different hormones and sugar signaling pathways in apple clones determine AR formation under water stress, but these are not entirely understood. To identify them, GL-3 stem cuttings were cultured on polyethylene glycol (PEG) treatment. The AR formation was dramatically decreased compared with the PEG-free control (CK) cuttings by increasing the endogenous contents of abscisic acid (ABA), zeatin riboside (ZR), and methyl jasmonate (JA-me) and reducing the indole-3-acetic acid (IAA) and gibberellic acid 3 (GA3) contents. We performed a transcriptomic analysis to identify the responses behind the phenotype. A total of 3204 differentially expressed genes (DEGs) were identified between CK and PEG, with 1702 upregulated and 1502 downregulated genes. Investigation revealed that approximately 312 DEGs were strongly enriched in hormone signaling, sugar metabolism, root development, and cell cycle-related pathways. Thus, they were selected for their possible involvement in adventitious rooting. However, the higher accumulation of ABA, ZR, and JA-me contents and the upregulation of their related genes, as well as the downregulation of sugar metabolism-related genes, lead to the inhibition of ARs. These results indicate that AR formation is a complicated biological process chiefly influenced by multiple hormonal signaling pathways and sugar metabolism. This is the first study to demonstrate how PEG inhibits AR formation in apple plants.
Highlights
A systemic analysis was performed on the formation of Adventitious root (AR) in GL-3 apple cuttings using polyethylene glycol (PEG) at different time points to better understand the phenotypical changes in response to drought stress
Within S2, no morphological changes were observed in either group; at S3, the AR emergence stage was visible in CK cuttings but not in PEGtreated cuttings (Figure 1A)
On S2, mitosis was seen in cambial cells, and AR primordia were observed on S3 in the CK group, which was missing in PEG-treated cuttings (Figure 1A)
Summary
Apple (Malus domestica) is a broadly cultivated profitable fruit tree. High-density plantation techniques are needed, which largely depend on the use of dwarf rootstocks. In the Loess Plateau region of China, numerous apple orchards have poor irrigation systems or no irrigation systems at all. Some orchards were constructed with interstocks (dwarfed intermediate anvils). The length of interstocks is 25 cm
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