Differential miRNA expression in Rehmannia glutinosa plants subjected to continuous cropping

BACKGROUND: The productivity of the medicinally significant perennial herb Rehmannia glutinosa is severely affected after the first year of cropping. While there is some information available describing the physiological and environmental causes of this yield decline, there is as yet no data regarding the changes in gene expression which occur when the species is continuously cropped. RESULTS: Using a massively parallel (Solexa) DNA sequencing platform, it was possible to identify and quantify the abundance of a large number of R. glutinosa miRNAs. We contrasted the miRNA content of first year crop plants with that of second year crop ones, and were able to show that of 89 conserved (belonging to 25 families) and six novel miRNAs (six families), 29 of the former and three of the latter were differentially expressed. The three novel miRNAs were predicted to target seven genes, and the 29 conserved ones 308 genes. The potential targets of 32 of these differentially expressed miRNAs involved in the main transcription regulation, plant development and signal transduction. A functional analysis of the differentially expressed miRNAs suggested that several of the proposed targets could be directly or indirectly responsible for the development of the tuberous root. CONCLUSION: We have compared differential miRNAs expression in the first year crop (FP) R. glutinosa plants and second year crop (SP) ones. The outcome identifies some potential leads for understanding the molecular basis of the processes underlying the difficulty of maintaining the productivity of continuously cropped R. glutinosa.