Identification and functional analysis of a CbSHR homolog in controlling adventitious root development in Catalpa bungei

Clonal forestry is an important approach for intensive management as it involves vegetative propagation, which does not entail gene separation and recombination, thereby retaining the excellent traits of the parent trees. Exploring essential genes involved in rooting of cuttings seems urgent in Catalpa bungei as it is the capital method in vegetative propagation. In this study, we identified a homolog of the SHR gene involved in the development of adventitious roots (ARs) in C. bungei through multiple alignment, homologous cloning, qPCR detection, and transgenic techniques. The CbSHR gene encodes a protein of 445 amino acids, and the expression of the CbSHR gene reaches its peak at the callus differentiation stage (S4, about 30 days after cutting) during AR development. By overexpressing the CbSHR gene in tobacco, the number of roots and their length were increased compared with the wild-type line, thus identifying a pivotal homolog, the CbSHR gene in C. bungei, which promotes the initiation and elongation of ARs. This result provided a candidate gene for genetic improvement of cutting, and will also contribute to understanding the molecular mechanisms of AR development in C. bungei.