Abstract
As auxins are among the most important phytohormones, the regulation of auxin homeostasis is complex. Generally, auxin conjugates, especially IAA glucosides, are predominant at high auxin levels. Previous research on terminal glucosylation focused mainly on the O-position, while IAA-N-glucoside and IAA-Asp-N-glucoside have been neglected since their discovery in 2001. In our study, IAA-Asp-N-glucoside was found to be specifically abundant (as high as 4.13 mg/g) in the seeds of 58 ginkgo cultivars. Furthermore, a novel N-glucosyltransferase, termed GbNGT1, was identified via differential transcriptome analysis and in vitro enzymatic testing. It was found that GbNGT1 could catalyze IAA-Asp and IAA to form their corresponding N-glucosides. The enzyme was demonstrated to possess a specific catalytic capacity toward the N-position of the IAA-amino acid or IAA from 52 substrates. Docking and site-directed mutagenesis of this enzyme confirmed that the E15G mutant could almost completely abolish its N-glucosylation ability toward IAA-Asp and IAA in vitro and in vivo. The IAA modification of GbNGT1 and GbGH3.5 was verified by transient expression assay in Nicotiana benthamiana. The effect of GbNGT1 on IAA distribution promotes root growth in Arabidopsis thaliana.
Highlights
IntroductionThe plant hormone auxin (indole-3-acetic acid, IAA)was discovered over 70 years ago. our understanding of the IAA signaling pathway has thrived in the last few decades, key metabolic pathway enzymes are missing, and the regulation of auxin metabolism is poorly understood[1]
The plant hormone auxinwas discovered over 70 years ago
By screening candidate GbUGTs from the differential transcriptomes of ginkgo seeds and leaves, we found that a unique GbNGT1 can perform catalysis at the N-position to form IAA-Asp-N-glucoside and IAA-N-glucoside
Summary
The plant hormone auxin (indole-3-acetic acid, IAA)was discovered over 70 years ago. our understanding of the IAA signaling pathway has thrived in the last few decades, key metabolic pathway enzymes are missing, and the regulation of auxin metabolism is poorly understood[1]. The plant hormone auxin (indole-3-acetic acid, IAA). Our understanding of the IAA signaling pathway has thrived in the last few decades, key metabolic pathway enzymes are missing, and the regulation of auxin metabolism is poorly understood[1]. IAA levels can be attenuated by conjugation (mainly to amino acids and sugars)[2]. IAA conjugates are regarded as either reversible or irreversible storage compounds, and their functions and regulatory genes during plant growth and development are still under investigation[3]. Amide-linked IAA conjugates (IAA-AA) constitute ~90% of the IAA pool in Arabidopsis thaliana[4].
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