Isolation and identification of a vegetative organ-specific promoter from maize

To avoid the unregulated overexpression of the exogenous genes, specific or inducible expression is necessary for some exogenous genes in transgenic plants. But little is known about organ- or tissue-specific promoters in maize. In the present study, the expression of a maize pentatricopeptide repeat (PPR) protein encoding gene, GRMZM2G129783, was analyzed by RNA-sequencing data and confirmed by quantitative real time PCR. The results showed that the PPRGRMZM2G129783 gene specifically expressed in vegetative organs. Consequently, a 1830bp sequence upstream of the start codon of the promoter for GRMZM2G129783 gene was isolated from maize genome (P-1830). To validate whether the promoter possesses the vegetative organ-specificity, the full-length and three 5-end deletion fragments of P-1830 of different length (1387, 437, and 146bp) were fused with glucuronidase (GUS) gene to generate promoter::GUS constructs and transformed into tobacco. The transient expression and fluorometric GUS assay in transgenic tobacco showed that all promoter could drive the expression of the GUS gene, the -437 to -146bp region possessed some crucial elements for root-specific expression, and the shortest and optimal sequence to maintain transcription activity was 146 and 437bp in length, respectively. These results indicate that the promoter of the PPRGRMZM2G129783 gene is a vegetative organ-specific promoter and will be useful in transgenic modification of commercial crops for moderate specific expression after further evaluation in monocotyledons.