The Cotton GhRac6 Gene Encoding a Plant ROP/RAC Protein Improves the Plant Defense Response to Aphid Feeding

The plant ROP/RAC protein belongs to a subfamily of Rho family GTPases that inimitably exists in plants. It is considered an all-powerful molecular switch that modulates various plant developmental processes and plant defense responses to multifarious stresses. However, their exact roles are currently not entirely clear. Herein, the role of GhRac6, a ROP/RAC member from Gossypium hirsutum, was explored in the plant defense response to aphid feeding using transgenic technology. The deduced sequence of the GhRac6 protein is highly homologous to that of ROP/RAC proteins from other plants. GhRac6 expression was significantly upregulated in cotton leaves after damage by cotton aphids or wounding. The results of choice and no-choice tests showed that the number of aphids on GhRac6-overexpressing transgenic Arabidopsis was more than that on wild-type plants, while the secreted quantity of aphid honeydew in transgenic Arabidopsis was less than that in wild-type plants. Furthermore, the soluble sugar content and the proline content were higher in transgenic than in wild-type Arabidopsis to a certain extent. The activity of PAL and CAT in transgenic Arabidopsis was also higher than that in wild-type plants. Callose deposits were more abundant in transgenic than in wild-type Arabidopsis. The expression of related defense genes in the salicylic acid signaling pathway was considerably higher in transgenic than in wild-type Arabidopsis. These results collectively demonstrated that the cotton ROP gene GhRac6 improved the plant defense response to aphid feeding by regulating some aphid resistance indexes.