Molecular Regulation of Bud Regeneration from Callus of Hybrid Sweetgum (Liquidambar styraciflua × Liquidambar formosana)

Abstract

Adventitious bud regeneration is an effective means of rapid propagation of plants, which can be used in the study of plant development and genetic transformation. It can be divided into direct and indirect adventitious bud regeneration. Of the two kinds of adventitious bud regeneration mentioned, indirect adventitious bud regeneration includes callus formation in vitro and organ regeneration. In the process of callus formation, some cells acquire the pluripotency of tissue regeneration, which is the key to regeneration of adventient buds. It is not clear which molecular processes and genetic factors are involved in establishing cellular pluripotency. The object of the study is hybrid sweetgum (Liquidambar styraciflflua × L. formosana). At present, the reproductive efficiency of hybrid sweetgum is low and the reproductive cycle is long. Improving its reproductive efficiency by improving the differentiation speed of callus may be a decent approach. In order to explore the mechanism of pluripotency acquisition during forming hybrid sweetgum callus, we used RNA-seq to perform transcriptomic analysis of the regenerable calli (RC) and non-regenerable (NRC) calli of hybrid sweetgum. A dataset of differentially expressed genes (DEG) was obtained and several genes probably involved in bud formation were analyzed to explain the molecular processes of acquiring and maintaining pluripotency. In this study, a total of 665 significantly expressed DEGs were identified in the RC and NRC of hybrid sweetgum, among which, 585 differentially expressed genes were up-regulated and 80 differentially expressed genes were down-regulated. GO, KEGG analysis and qRT-PCR results showed phenylpropanoid is a key factor regulating the bud regeneration of hybrid sweetgum; WOX1, WOX11, BGLU12 and BGLU13 were also important regulatory factors. These results provide a pivotal reference point for future sweetgum propagation research.