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The Key to Drought-Tolerance Found in Maize Genes
Scientists have discovered a transcription factor in plants to promote the expression of drought-responsive genes, paving the way for developing drought-tolerant maize varieties.

Drought is one of the most destructive forms of abiotic stress that can gravely impact agricultural yield and compromise global food security. In recent years, droughts have become increasingly severe and prolonged, leaving staple crops like maize vulnerable and the future of food supplies uncertain.

To combat the effects of drought and extreme weathers, scientists have been exploring ways to develop more resilient maize varieties with much focus centred on achieving a better understanding of the underlying mechanisms of drought tolerance in crops.

One group of researchers was particularly interested in the genetic make-up of drought-resistant maize and conducted a transcriptome analysis and bin map subtraction of some extreme phenotypic lines from a drought-related recombinant line population. Their findings revealed that a specific transcription factor shows promising potential to help improve crop resilience against drought by activating the expression of drought-responsive genes.

Recombinant inbred line populations are widely used for genetic mapping to identify regions of the genome linked to a trait. In this case, the researchers were hoping to locate genes responsible for drought response. To create these populations, parent strains are crossed to produce recombinant offspring, that are then bred with one another to create genetically identical or isogenic progeny. These isogenic strains can be used as a permanent population source for trait mapping and analysis.

The team, led by Professor Xie Qi from the Institute of Genetics and Developmental Biology (IGDB) of the Chinese Academy of Sciences, screened four maize lines with different drought-responsive characteristics. Two drought-tolerant lines, RIL70 and RIL73, and two drought-sensitive lines, RIL44 and RIL93, were chosen and subjected to RNA-sequence analyses.

Based on their findings, it was revealed that there is a difference in gene expression not only between drought-tolerant and drought-sensitive lines but also between the tolerant lines, RIL70 and RIL73, implying that the mechanism of drought tolerance of RIL70 is different from RIL73.

To pinpoint their exact differences, the team examined their gene expression patterns and discovered that a basic helix-loop-helix (bHLH) type transcription factor ZmbHLH124T-ORG was involved in the maize drought response of the RIL73 line.

Through transgenic analysis, they observed that ZmbHLH124T-ORG is up-regulated during drought stress in maize and rice plants. The overexpression of ZmbHLH124T-ORG was also found to promote the activation of drought-responsive genes, improving survival rates and reduced water loss when plants were subjected to drought-like conditions.

The team further sought to uncover the mechanism of action behind ZmbHLH124T-ORG and through their investigation, they reported that this transcription factor exerts its effects by binding directly to cis-acting recognition sites in the ZmDREB2A promoter to enhance its expression. ZmDREB2A is a widely-known drought response transcription factor that is isolated from maize and activated as a result of exposure to cold temperatures, dehydration, high salinity, and heat stress.

With the newfound potential of ZmbHLH124T-ORG, scientists hope to breed more resilient and tolerant crops to mitigate the effects of drought and climate change, and pave the way for sustainable food security.

Source: Wei et al. (2021). ZmbHLH124 identified in maize recombinant inbred lines contributes to drought tolerance in crops. Plant Biotechnology Journal.

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