Functional Analysis of Aux/IAA s and SAUR s on Shoot Growth of Lagerstroemia indica through Virus-Induced Gene Silencing (VIGS)

The plant hormone auxin plays an important role in cell division and the elongation of shoots to affect the plant architecture, which has a great impact on the plant yield, fruit quality and ornamental value; however, the regulatory mechanism of auxin controlling shoot growth is unclear in crape myrtle. In this study, two auxin/indole-3-acetic acid (Aux/IAA) genes and four small auxin upregulated RNA (SAUR) genes of auxin response gene families were isolated from dwarf and non-dwarf progenies of Lagerstroemia indica and then functionally characterized. Sequence alignment revealed that the six genes contain typical conserved domains. Different expression patterns of the six genes at three different tissue stages of two types of progenies showed that the regulation mechanism of these genes may be different. Functional verification of the six genes upon shoot growth of crape myrtle was performed via virus-induced gene silencing. When the LfiAUX22 gene was silenced, a short shoot phenotype was observed in non-dwarf progenies, accompanied by decreased auxin content. Therefore, we preliminarily speculated that LfiAUX22 plays an important role in the shoot growth of crape myrtle, which regulates the accumulation of indole-3-acetic acid (IAA) and the elongation of cells to eventually control shoot length.