Identification of Drought-Stress Responsive MicroRNAs in Tropical Maize

Abstract

Maize is the major food crop worldwide far exceeding rice and wheat in terms of global production. MicroRNA (miRNA) mediated gene regulation has been found to play an important role in drought stress adaptation. In our study, the small RNA profiles of two contrasting maize genotypes were studied to identify differentially expressed miRNAs and their target genes under drought. Drought tolerant genotype HKI-335 and drought susceptible MGUD-22 was grown under glasshouse conditions and drought was imposed at the seedling stage. Leaf RNA samples of both genotypes were subjected to small RNA profiling through Next Generation Sequencing (NGS) for miRNA identification. Photosynthetic rate, stomatal conductance and Relative water content were found to be drastically reduced in MGUD-22 under drought. MiRNA differential expression analysis revealed 30 known miRNAs in HKI-335 and 44 miRNAs in MGUD-22. Novel miRNAs found were 132 in HKI-335 and 178 in MGUD-22. MiR827; miR528a,b; miR396b,e,f were found to be common in both the lines. MiR169a; miR2118b,c; miR397a were unique to HKI-335 whereas, miR408b; miR162; miR1432 were unique to MGUD-22. Treatment wise comparison under the control and drought conditions revealed 35 known miRNAs under control whereas 49 under drought conditions. Novel miRNAs identified were 172 and 147 respectively. MiR408a; miR169a,b,m; miR156a,j were common in both control and treated conditions. Target prediction of miRNAs was done using psRNATarget webserver. Different transcription factors were identified as targets of majority of the miRNAs. Detailed study of the interaction of these mirna-mRNA targets will further help in decoding the gene regulatory network under drought stress.