Physio-chemical and molecular modulation reveals underlying drought resilience mechanisms in Cucumber (Cucumis sativus L.)

The present study is the first report for a comprehensive understanding of key physio-chemical traits and important genes associated with drought tolerance in cucumbers. Drought stress is one of the severe threats to global cucumber production. Cucumber is a model plant for physiological and molecular studies. However, the physio-biochemical and molecular basis of drought tolerance in cucumbers needs to be better reported. This study evaluated a diverse set of cucumber core for drought response and identified contrasting genotypes for further studies. Under stress conditions, drought-tolerant genotypes exhibited minimal effects on root system architectural traits, facilitating the water uptake from deeper soil. These contrasting genotypes' physiological, biochemical, phenological and molecular responses were studied further under field conditions. Tolerant genotypes showed greater photosynthetic stability, higher transpiration rate, water use efficiency, greater membrane stability and higher canopy temperature depression in response to stress with the limited role of Fv/Fm. Tolerant genotypes exhibited a lower reduction of pollen viability and higher yield stability under field conditions. A lower concentration of stomata and reduced stomatal conductivity in the tolerant genotype was crucial for maintaining osmotic potential. At the cellular level, the increased activity and stronger expression of ROSscavenging enzymes, SOD, CAT, APX and soluble protein content provided stability to the cell membrane. Maintenance of hydration status in cells was enabled through higher proline accumulation. LEA4 and HSP70 were crucial molecular chaperones for providing stability to cell membrane protein under stress conditions. Differential expression of NAC, AP2/ERF, MBF and MybTF were integral parts of the molecular network associated with drought stress tolerance. A comprehensive understanding of physio-chemical response and molecular network will facilitate the identification of candidate genes, their functional validation and the design of resilient cultivars. This study provides a solid foundation to design and develop climate-smart cucumber genotypes with effective drought tolerance.