Pearl millet has a natural tolerance to salinity, a trait attributed to genes. The expression of these genes is modulated by microRNAs, a versatile group of small regulatory RNAs. But which microRNAs are involved in pearl millet’s salinity tolerance?
Shashi K Gupta from ICRISAT Hyderabad collaborated with researchers in the US, Japan and China to investigate. They sowed pearl millet seeds and, eighteen days after the seeds sprouted, they irrigated some plants with salty water and the rest with normal water.
Six days later, when the plants started exhibiting salinity stress, the researchers extracted and sequenced RNA from the leaves.
The sequenced data was then compared with microRNA reference databases of many plants including those of wheat, potatoes, sugarcane, etc. and the researchers thus identified 81 microRNAs that are conserved in different plants.
But how about microRNAs that are specific to salinity tolerance in pearl millet?
In the RNA sequence data, the team searched for the sequence that forms the typical hairpin structures in microRNAs. They found 14 microRNAs unique to pearl millet under salinity stress.
To find which genes are targeted by these microRNAs, the researchers aligned the sequence data of the microRNAs against the sequence data of RNAs available in databases. Thus they could identify 448 messenger RNAs targeted by the 95 microRNAs.
Most of the targeted messenger RNAs coded for proteins involved in ion transportation, protein detoxification, cell signalling and tolerance to stress. About one-fourth of the genes encode proteins that regulate the rate of transcription – a higher level control of gene expression.
The team then analyzed the pathways impacted by the microRNAs and found that the auxin signaling pathway is rich in the microRNA target genes. The mechanism of tolerance to salinity is thus highly dependent on the plant hormone signalling pathway genes, say the researchers.
The understanding of the genes involved in salinity tolerance and the mechanisms of control of gene expression in pearl millet will help us when we breed other crops for salinity tolerance. The data generated on the microRNAs involved in salinity tolerance can now be used by other researchers to align their sequence data.
South African Journal of Botany, 132: 395-402 (2020);
University of Goa
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