Transcriptomic and Anatomic Profiling Reveal Etiolation Promotes Adventitious Rooting by Exogenous Application of 1-Naphthalene Acetic Acid in Robinia pseudoacacia L.

Muhammad Zeeshan Munir,Zijie Zhang,Muhammad Imran,Muhammad Atif Muneer,Tariq Pervaiz,Ali Bakhsh,Chao Han,Yuhan Sun,Saleem Ud Din,Zaib Un Nisa,Yun Li

doi:10.3390/f12060789

Abstract

The process of etiolation contributes significantly to vegetative propagation and root formation of woody plants. However, the molecular interaction pattern of different factors for etiolated adventitious root development in woody plants remains unclear. In the present study, we explored the changes at different etiolation stages of adventitious root formation in Robinia pseudoacacia. Histological and transcriptomic analyses were performed for the etiolated lower portion of hypocotyls to ascertain the adventitious root responses. We found that the dark-treated hypocotyls formed roots earlier than the control. Exogenous application of NAA (0.3 mg/L) stimulated the expressions of about 310 genes. Among these, 155 were upregulated and 155 were downregulated. Moreover, differentially expressed genes (DEGs) were significantly enriched in multiple pathways, including the biosynthesis of secondary metabolites, metabolic pathway, plant hormone signal transduction, starch and sucrose metabolism, phenylpropanoid biosynthesis, and carbon metabolism. These pathways could play a significant role during adventitious root formation in etiolated hypocotyls. The findings of this study can provide novel insights and a foundation for further studies to elucidate the connection between etiolation and adventitious root formation in woody plants.

Highlights

R. pseudoacacia is native to North America and was first introduced to China in 1877 [1].R. pseudoacacia possesses the most significant ecological and economic characteristics, including excellent coppicing, fast growth, high yield, and adaptability to a wide range of environments [2]
R. pseudoacacia-148 seeds were chosen for this study due to their relatively better rooting performance than other clones and differential response to a mild NAA treatment during adventitious root formation (Figure 1)
AtMYB96 acts as an important molecular link between salicylic acid and abscisic acid crosstalk, through which it can enhance the resistance against pathogens in Arabidopsis thaliana [36]. These results indicate that the differential expression of type B-ARRs may play a role in R. pseudoacacia adventitious root formation induced by auxin

Summary

Introduction

R. pseudoacacia is native to North America and was first introduced to China in 1877 [1].R. pseudoacacia possesses the most significant ecological and economic characteristics, including excellent coppicing, fast growth, high yield, and adaptability to a wide range of environments [2]. Several reports have shown that in vitro propagation of R. pseudoacacia is an effective method to produce large numbers of clonal plants [3] because woody species are usually more difficult to root than herbaceous plants [4]. The low rooting rate is a limiting and crucial factor of R. pseudoacacia, making it difficult to grow in a variety of environments [5]. It has been found that different stresses such as wounding, etiolation, and the application of phytohormones have a significant effect on adventitious root formation [6]. Three major factors, including light/dark, phytohormones, and nitrogen oxide, have been recognized to induce adventitious root formation [7]. Understanding the formation of adventitious roots through potential factors, including etiolation and phytohormones, is a matter of great interest to offset the rooting problem in

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