Histological, Physiological and Transcriptomic Analysis Reveal Gibberellin-Induced Axillary Meristem Formation in Garlic (Allium sativum).

Hongjiu Liu,Mingming Cui,Zhihui Cheng,Rui Deng,Xiaofang Qi,Jingcao Gao,Yanbin Wen

doi:10.3390/plants9080970

Hongjiu Liu, Mingming Cui + Show 5 more

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https://doi.org/10.3390/plants9080970

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Abstract

The number of cloves in a garlic bulb is controlled by axillary meristem differentiation, which directly determines the propagation efficiency. Our previous study showed that injecting garlic plants with gibberellins (GA3) solution significantly increased clove number per bulb. However, the physiological and molecular mechanism of GA-induced axillary bud formation is still unknown. Herein, dynamic changes in histology, phytohormones, sugars and related genes expression at 2, 4, 8, 16 and 32 days after treatment (DAT) were investigated. Histological results indicated two stages (axillary meristem initiation and dormancy) were in the period of 0–30 days after GA3 treatment. Application of GA3 caused a significant increase of GA3 and GA4, and the downregulation of AsGA20ox expression. Furthermore, the change trends in zeatin riboside (ZR) and soluble sugar were the same, in which a high level of ZR at 2 DAT and high content of soluble sugar, glucose and fructose at 4 DAT were recorded, and a low level of ZR and soluble sugar arose at 16 and 32 DAT. Overall, injection of GA3 firstly caused the downregulation of AsGA20ox, a significant increase in the level of ZR and abscisic acid (ABA), and the upregulation of AsCYP735 and AsAHK to activate axillary meristem initiation. Low level of ZR and soluble sugar and a high level of sucrose maintained axillary meristem dormancy.

Highlights

Shoot branching, originating from an axillary bud, is an important determinant of plant architecture and significantly influences crop yield [1]
Axillary meristem appeared after 30 days of GA3 treatment; on the contrary, there was no axillary meristem in the control at the same time (Figure 1A,B)
At 90 days after treatment (DAT), significantly more axillary meristem formation took place, while no axillary meristem was yet recorded in control (Figure 1C,D)

Summary

Introduction

Shoot branching, originating from an axillary bud, is an important determinant of plant architecture and significantly influences crop yield [1]. Axillary bud development is involved in two stages: axillary meristem initiation in the leaf axil and axillary bud outgrowth or dormancy [2]. The role of auxins, cytokinins (CKs), strigolactones (SLs) and brassinosteroid (BR) in shoot branching was reported, revealing a complex network of signals that combine to regulate an axillary meristem into a branch [3]. Sugars and their signaling networks played a critical role at the early stages of axillary bud outgrowth [4,5]. The second most important Allium crop after the bulb onion, is cultivated and consumed worldwide for its flavor and medicinal value [13]. The clove includes a bud, a storage leaf and a protective leaf, which is equated with

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