Molecular characterization of the promoter of the stress-inducible ZmMYB30 gene in maize

The ZmMYB30 is a member of the myeloblastosis (MYB) transcription factor superfamily, which has been shown to be a transcription regulator in abiotic stress tolerance in maize (Zea mays). To further identify the biological function of ZmMYB30 and reveal how its expression is induced in response to stress, we isolated the ZmMYB30 promoter and conducted a functional analysis. A 1461-bp promoter fragment was cloned and sequenced. Motif prediction using PlantCARE revealed several stress-responsive elements in the promoter sequence. Deletions in the promoter sequence affected the activity of the promoter and demonstrated that putative stress-responsive motifs, including TC-rich repeats (ATTCTCTAAC), abscisic acid responsive element (ABRE, ACGTG), and MYB binding site (MBS, CAACTG), played important roles in regulating the expression of ZmMYB30. Promoter β-glucuronidase (GUS) analysis also showed that GUS expression under the control of the ZmMYB30 promoter responded to drought and salinity. Many natural variations in the ZmMYB30 promoter sequence were found among 31 inbred maize lines, including 22 single nucleotide polymorphisms (SNPs), 17 insertion and deletion (InDels), and approximately 400-bp long deletions. The ZmMYB30 expression varied greatly among the different inbred lines. The long fragment deletion in the promoter region did not impair the ZmMYB30 expression, whereas SNP (-374) in the MBS motif in the 62R and LH82 lines greatly decreased the ZmMYB30 expression. A site-specific mutation in the MBS motif also decreased the expression of the reporter GUS gene driven by the ZmMYB30 promoter sequence. The expressions of three stress-responsive genes ZmSOS1, ZmSOS2, and ZmABF3 were found to be consistent with the ZmMYB30 expression. Our results provide new evidence to support the role of ZmMYB30 as an important regulator in maize stress tolerance.