Insights into the Root Sprouts of Toona fargesii in a Natural Forest: From the Morphology, Physiology, and Transcriptome Levels

Abstract

Toona fargesii (T. fargesii) is a deciduous tree of the Meliaceae family which is utilized for high-value timber. Interestingly, root sprouting is a typical reproductive pattern in T. fargesii. Nevertheless, the genetics underlying this phenomenon are still unclear. Here, three type of roots of T. fargesii were used for histological observation, plant endogenous hormone determination, non-structural carbohydrate (NSC) determination, and sequencing using the Illumina next-generation and PacBio SMRT platforms. Our results indicated that root sprouts originated from cork cambiums. Furthermore, indole-3-acetic acid (IAA), zeatin riboside (ZR), gibberellic acid 3 (GA3), and abscisic acid (ABA) content was significantly increased, while soluble sugar content was significantly decreased in the root sprouts. In addition, transcriptomic analysis suggested a total of 36.19 G of raw data from which 210 differentially expressed genes (DEGs) of were identified in RS vs. SR. Of these, the candidate DEGs were largely enriched in the citrate cycle, gluconeogenesis, starch and sucrose metabolism, and plant hormone signal transduction pathways. We therefore speculated that the accumulation of cytokinin and auxin might be induced by ATP-binding cassette-B 19 (ABCB19) and ABCG14, which were necessary for root sprouting. Additionally, transcription factors SQUAMOSA promoter binding protein-like 18 (SPL18) and NAM, ATAF1/2, and CUC2-14 (NAC14) were found in response to environmental water and epigenetic modification in RS. Overall, this study was to unravel the physiological and transcriptomic levels of the development of root sprouting in T. fargesii.