miRNA alteration is an important mechanism in sugarcane response to low-temperature environment.

BACKGROUND: Cold is a major abiotic stress limiting the production of tropical and subtropical crops in new production areas. Sugarcane (Saccharum spp.) originates from the tropics but is cultivated primarily in the sub-tropics where it frequently encounters cold stress. Besides regulating plant growth, miRNAs play an important role in environmental adaption. RESULTS: In this study, a total of 412 sugarcane miRNAs, including 261 known and 151 novel miRNAs, were obtained from 4 small RNA libraries through the Illumina sequencing method. Among them, 62 exhibited significant differential expression under cold stress, with 34 being upregulated and 28 being downregulated. The expression of 13 miRNAs and 12 corresponding targets was validated by RT-qPCR, with the majority being consistent with the sequencing data. GO and KEGG analysis indicated that these miRNAs were involved in stress-related biological pathways. To further investigate the involvement of these miRNAs in tolerance to abiotic stresses, sugarcane miR156 was selected for functional analysis. RT-qPCR revealed that miR156 levels increased in sugarcane during cold, salt and drought stress treatments. Nicotiana benthamiana plants transiently overexpressing miR156 exhibited better growth status, lower ROS levels, higher anthocyanin contents as well as the induction of some cold-responsive genes, suggesting its positive role in the plant cold stress response. CONCLUSIONS: This study provides a global view of the association of miRNA expression with the sugarcane response to cold stress. The findings have enriched the present miRNA resource and have made an attempt to verify the involvement of miR156 in plant response to cold stress.

ScMED7, a sugarcane mediator subunit gene, acts as a regulator of plant immunity and is responsive to diverse stress and hormone treatments.

The Mediator complex, is an essential component of the RNA polymerase II general transcriptional machinery in eukaryotes. Mediator subunit 7 (MED7), a key subunit in the central module of this complex, plays an important role in gene transcriptional regulation. The present study isolated the full-length cDNA of the MED7 gene of sugarcane, hereby designated as ScMED7, which was characterized to harbor a 525-bp open reading frame that is predicted to encode a 174-amino acid protein with a molecular mass of 19.9 kDa and was localized to the nucleus and cytoplasm. ScMED7 contains one typical conserved domain of MED7 proteins and shares 98% homology with that from Sorghum bicolor (XP_002447862.1). ScMED7 was constitutively expressed, yet significantly higher in bud tissues. ScMED7 transcription was obviously induced by heavy metal (CdCl2), low temperature (4 °C), and hormone (SA and MeJA) treatments, while inhibited by osmotic stresses of NaCl and PEG. The role of ScMED7 in plant immunity was demonstrated by transient overexpression in tobacco, which in turn induces the expression of six out of nine defense-related marker genes, including all the three hypersensitive response genes. The responses of defense-related marker genes in the mock and in the ScMED7 transiently overexpressed leaves challenged by pathogenic Pseudomonas solanacearum and Fusarium solani var. coeruleum suggest that ScMED7 acts as a negative regulator during pathogen infections, whereas only fungal infection was clearly phenotypically expressed. In sum, ScMED7 plays an important role in modulating sugarcane responses to biotic and abiotic stresses, and may have dual roles in hypersensitive responses and basal defense against pathogens.