Comparative Transcriptome Analysis Reveals the Interaction of Sugar and Hormone Metabolism Involved in the Root Hair Morphogenesis of the Endangered Fir Abies beshanzuensis

Abstract

Abies beshanzuensis, an extremely rare and critically endangered plant with only three wild adult trees globally, is strongly mycorrhizal-dependent, leading to difficulties in protection and artificial breeding without symbiosis. Root hair morphogenesis plays an important role in the survival of mycorrhizal symbionts. Due to the lack of an effective genome and transcriptome of A. beshanzuensis, the molecular signals involved in the root hair development remain unknown, which hinders its endangered mechanism analysis and protection. Herein, transcriptomes of radicles with root hair (RH1) and without root hair (RH0) from A. beshanzuensis in vitro plantlets were primarily established. Functional annotation and differentially expressed gene (DEG) analysis showed that the two phenotypes have highly differentially expressed gene clusters. Transcriptome divergence identified hormone and sugar signaling primarily involved in root hair morphogenesis of A. beshanzuensis. Weighted correlation network analysis (WGCNA) coupled with quantitative real-time PCR (qRT-PCR) found that two hormone–sucrose–root hair modules were linked by IAA17, and SUS was positioned in the center of the regulation network, co-expressed with SRK2E in hormone transduction and key genes related to root hair morphogenesis. Our results contribute to better understanding of the molecular mechanisms of root hair development and offer new insights into deciphering the survival mechanism of A. beshanzuensis and other endangered species, utilizing root hair as a compensatory strategy instead of poor mycorrhizal growth.

MYB6/bHLH13‐AbSUS2 involved in sugar metabolism regulates root hair initiation of Abies beshanzuensis

“…RNA extraction and reverse transcription were performed as described by Liu et al . (2023). PP2A served as the reference gene (Liu et al ., 2023).…”

“…The SUS pathway, which is involved in sucrose degradation, was shown to partly compensate for energy restriction in tomato roots (Shi et al ., 2008). In our previous study, we found that AbSUSs were significantly differentially expressed between radicles with and those without root hairs in Abies beshanzuensis , suggesting that they regulate root hair development (Liu et al ., 2023). The regulatory role of SUSs in root hair morphogenesis is complex and is governed by an intricate transcriptional network.…”

“…Abies beshanzuensis is known as the ‘panda’ of plants, with only three surviving wild adult individuals world‐wide, found in the main peak of Mt. Baishanzu in Zhejiang province, China (Liu et al ., 2023). Abies beshanzuensis is unique in that without symbiosis, its root system has a limited capacity for nutrient absorption and utilization, which complicates artificial breeding.…”

“…1). Furthermore, the in vitro RH1 plantlets grew distinctly better than the RH0 ones after subsequent transplantation (Liu et al ., 2023).…”

“…For the survival of the species, it is imperative to elucidate the molecular mechanism underlying A. beshanzuensis root hair growth and development. In this study, we characterized a sucrose synthase gene ( AbSUS2 ) previously found to show significant differential expression between the transcriptomes of in vitro A. beshanzuensis plantlets with and without root hairs (Liu et al ., 2023). Functional and expression pattern analysis of AbSUS2 indicated that it was a crucial negative regulator of root hair initiation in A. beshanzuensis .…”