MicroRNAs
(miRNAs), a type of short noncoding RNA molecule (21–23
nucleotides), mediate repressive gene regulation through RNA silencing
at the posttranscriptional level and play an important role in the
defense response to abiotic and biotic stresses. miRNAs of the plant
system have been studied in model crops for their diverse regulatory
role while less is known about their significance in other plants
whose genome and transcriptome data are scarce in the database, including
eggplant (
Solanum melongena
L.). In
the present study, a next-generation sequencing platform was used
for the sequencing of miRNA, and real-time quantitative PCR for miRNAs
was used to validate the gene expression patterns of miRNAs in
Solanum melongena
plantlets infected with the bacterial
wilt-causing pathogen
Ralstonia solanacearum
(
R. solanacearum
). Sequence analyses
showed the presence of 375 miRNAs belonging to 29 conserved families.
The miR414 is highly conserved miRNA across the plant system while
miR5658 and miR5021 were found exclusively in
Arabidopsis
thaliana
surprisingly, these miRNAs were found in
eggplants too. The most abundant families were miR5658 and miR414.
Ppt-miR414, hvu-miR444b, stu-miR8020, and sly miR5303 were upregulated
in Pusa purple long (PPL) (susceptible) at 48 h postinfection, followed
by a decline after 96 h postinfection. A similar trend was obtained
in ath-miR414, stu-mir5303h, alymiR847-5p, far-miR1134, ath-miR5021,
ath-miR5658, osa-miR2873c, lja-miR7530, stu-miR7997c, and gra-miR8741
but at very low levels after infection in the susceptible variety,
indicating their negative role in the suppression of host immunity.
On the other hand, osa-miR2873c was found to be slightly increased
after 96 hpi from 48 hpi. Most of the miRNAs under study showed relatively
lower expression in the resistant variety Arka Nidhi after infection
than in the susceptible variety. These results shed light on a deeper
regulatory role of miRNAs and their targets in regulation of the plant
response to bacterial infection. The present experiment and their
results suggested that the higher expression of miRNA leads to a decline
in host mRNA and thus shows susceptibility.