Identification of expression profiles of sorghum genes in response to greenbug phloem-feeding and characterization of the two sorghum defense-related genes, Xa1 and oxysterol-binding protein

Abstract

Scope and Method of Study: The greenbug phloem-feeding elicits unique interactions with plants. Using suppression subtractive hybridization (SSH) and subsequent microarray analyses, expression profiling of sorghum genes in response to greenbug feeding was performed to understand a regulation mechanism of molecular defense responses against greenbug phloem-feeding in sorghum. Among the expression profiles, two genes identified to encode Xa1 and Oxysterol binding protein (OSBP) were further characterized, and their regulatory mechanisms investigated by comparison of expression patterns of the two genes responsive to three different conditions such as greenbug infestation, methyl jasmonate treatment, and mechanical wounding.

Findings and Conclusions: A total of 157 genes identified to respond greenbug feeding was obtained by SSH and microarray analyses. These genes were classified into nine categories according to their metabolic functions. Several molecular regulators such as jasmonic acid, salicylic acid, abscisic acid, auxin, and gibberellic acid were involved in regulation of defense responses against greenbugs in sorghum. In our profiles, several genes which have not been reported in their roles in defense responses against greenbugs were obtained, including the genes encoding Xa1 (Xa1) and oxysterol binding protein (OSBP). Multiple aligning of deduced amino acid sequences of the two genes with other homologous proteins from other species showed high identity in amino acid sequences. Expression analyses of Xa1 and OSBP genes showed that regulations of both genes were not affected by MeJA, but conducted via independent pathways. The expression patterns of both genes showed high similarity between greenbug infested and mechanically wounded sorghum seedlings.