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Journal of Experimental Botany · 2025

Adaptive Divergence in
Tunisian Durum Wheat

An integrative RNA-Seq and whole-genome sequencing study of two Tunisian landraces — Chili and Mahmoudi — revealing transcriptional and genomic signatures of local adaptation.

🌊 Chili — humid-adapted (north / central Tunisia) ☀️ Mahmoudi — drought-tolerant (southern / interior Tunisia) 🧬 RNA-Seq + WGS · Triticum turgidum
The Science Story Background

How does a 10,000-year-old landrace adapt to its environment? We compared two divergent Tunisian durum wheat varieties across tissues and conditions.

1

Two Landraces, One Genome

Chili (humid northern and central Tunisia) and Mahmoudi (semi-arid to arid southern Tunisia, also grown in many other regions) are morphologically distinct landraces of T. turgidum still maintained by a limited number of traditional farmers.

2

Differential Expression

RNA-Seq across root and leaf tissues identified thousands of differentially expressed genes — revealing that stress-response pathways are constitutively activated in Mahmoudi even under controlled conditions.

3

Selective Sweeps

Whole-genome sequencing revealed 46 permutation-significant FST outlier windows (10 kb), marking regions of divergent selection — concentrated on chromosomes 1A, 2A, 5A, 6B, 1B, and 2B.

4

Breeding Implications

Cross-referencing DEGs with published stress QTLs identified 160+ validated candidate genes — potential targets for marker-assisted selection in Mediterranean wheat breeding programs.

The Landraces Speak Identity

Two ancient varieties, two strategies for survival. Here is what 10,000 years of selection has encoded in each genome — and what they offer the future of wheat breeding.

🌊
Chili
Northern and central Tunisia · Humid Mediterranean rainfed · 400–700 mm annual rainfall

"I grew where the sea breeze tempers the heat and seasonal rains arrive reliably. My strategy is efficiency, not armament. I invest in growth, in photosynthetic gain, in reducing oxidative load. I carry the machinery for reactive oxygen scavenging and precise protein turnover. I am not built for crisis — I am built to thrive when conditions allow. In a changing world, I am what agriculture has cultivated: optimised productivity."

19 ROS/oxidative-stress genes upregulated — active antioxidant machinery for efficient redox balance under productive growth.
🔄
25 ubiquitin–proteasome components elevated — tight developmental protein turnover for optimal growth regulation.
🛡️
33 NLR resistance genes expressed — broad immune repertoire maintained, reflecting a pathogen-rich humid environment.
☀️
Photosynthesis machinery robustly expressed — RuBisCO and chloroplast components active, prioritising carbon fixation.
💧
Aquaporin network and dehydrin backup — controlled water-use efficiency suited to seasonal rainfall patterns.

What I offer breeders
High yield potential Oxidative stress tolerance Broad disease resistance Efficient photosynthesis Chr 1A & 2A QTL alleles
☀️
Mahmoudi
Southern and interior Tunisia · Semi-arid to arid · <200 mm annual rainfall · cultivated since antiquity

"I was forged in the harshest soils of the Tunisian south, where rain is a rumour and the sun shows no mercy. My roots learned to scavenge, my leaves learned to hold on. I do not wait for stress to respond — I am always ready. My NLR guards are perpetually awake, my dehydrins never fully sleep, and my ubiquitin machinery quietly prunes damaged proteins before they accumulate. I am expensive to run, but I do not break."

🛡️
22 NLR disease-resistance genes constitutively upregulated — broad-spectrum immunity primed without pathogen challenge.
💧
Drought/ABA/dehydrin network switched on at baseline — LEA proteins, nucleases, and hnRNPs pre-deployed for osmotic stress.
🔄
Ubiquitin–proteasome system highly active — 15 F-box and E3-ligase genes clearing misfolded proteins continuously.
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8 heat-shock chaperones (DnaJ family) elevated — protein quality control at all times, not just under heat.
📡
7 receptor kinases upregulated — hypersensitive environmental sensing, translating subtle cues into rapid responses.

What I offer breeders
Drought tolerance Heat resilience Constitutive immunity Protein quality control Chr 5A & 6B QTL alleles

🧬 Gene Explorer Interactive

Browse and filter all differentially expressed genes. Click column headers to sort. Search by gene ID or product name.

Gene ID ↕ Product ↕ Category ↕ Comparison ↕ Direction ↕ log₂FC ↕ adj. p-value ↕

🗺️ Genomic Hotspots WGS

Per-chromosome population genomics. Click a chromosome bar to see details. Chromosomes with FST outliers indicate regions under divergent selection.

FST Outlier Windows per Chromosome (10 kb, permutation-significant)
Nucleotide Diversity (π) Ratio — Chili / Mahmoudi
Tajima's D — Both Landraces

🔍 Chromosome Details

Click a chromosome bar to inspect

⚙️ Functional Landscape RNA-Seq

Biological pathway enrichment across 16 AHRD-curated functional categories. Toggle direction to explore what each landrace activates.

Functional Categories — Landrace Comparison
Expression Volcano — Chili vs Mahmoudi
CATEGORY QUICK SUMMARY

🎯 Breeding Targets Validated

Cross-referenced DEGs validated against published stress QTLs in durum/bread wheat. These are priority candidates for marker-assisted selection.

Top 20 Candidates by |log₂FC| — Chili vs Mahmoudi