Abstract
Activity of root apical meristem (RAM) at the root apex is critical for stress-mediated modulation of root-architecture. Chickpea, like other legumes, possesses a basic open root meristem. Deep sequencing was used to perform microRNA expression profiling in root apex of chickpea (Cicer arietinum L.) in order to investigate post-transcriptional regulation of gene expression in this tissue in response to salinity and water deficit. Five small RNA libraries prepared from chickpea root apices at different stages of stress treatments were sequenced to obtain 284 unique miRNA sequences including 60 novel miRNAs belonging to total 255 families. Two hundred and fiftynine miRNAs were differentially expressed in stress. Six hundred and nine mRNA targets involved in diverse cellular processes were predicted for 244 miRNAs. Stress-responsive expression patterns of selected miRNAs, inverse expression patterns of their target genes and the target-cleavage sites were validated. Three candidate miRNA-target gene relationships were validated in transient expression system in chickpea. The miRNA expression profiling under salinity and water deficiency in a legume root apex and the reported function of their target genes suggested important roles of miRNA-mediated post-transcriptional regulation of gene expression involved in re-patterning of root hair cells, lateral root formation and high-affinity K+-uptake under these stresses.
Highlights
Decrease in ground water level and increase in salinity limit plant growth and eventually yield in all agricultural ecosystem
An early study showed upregulation of MicroRNA 393 (miR393), miR397b and miR402 expression under dehydration and salt stress in Arabidopsis21. miR159 overexpression caused reduction in MYB33 and MYB101 transcript accumulation resulting in abscisic acid (ABA)-hyposensitive Arabidopsis plant22. miR169a targets nuclear factor YA5 to reduce its expression and causes enhanced leaf water loss resulting in drought sensitivity[23]
Instead of root cap cells organized in layers as in Arabidopsis, chickpea root cap cells were more in numbers and did not peel-off in layers. 3 mm section showed undifferentiated densely packed cells surrounded by border cells and root cap
Summary
Decrease in ground water level and increase in salinity limit plant growth and eventually yield in all agricultural ecosystem. An analysis of small RNA population from root tips of soybean seedlings under normal and salt stress conditions identified total 71 miRNA candidates belonging to 59 known and novel miRNA families. It was suggested that auxin signaling plays a crucial role in regulation of the miRNAs and root development in soybean[31] All these information highlight a major role of miRNA in shaping root RSA by regulating gene expression in root and, thereby, RAM activity. We report here the dynamics of miRNA expression in chickpea root apex at different stages of water deficit and salinity stresses by high throughput sequencing of small RNA libraries to understand regulation of gene expression by miRNA in this tissue under these stresses
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