Stress-Responsive Gene Expression, Metabolic, Physiological, and Agronomic Responses by Consortium Nano-Silica with Trichoderma against Drought Stress in Bread Wheat

The exploitation of drought is a critical worldwide challenge that influences wheat growth and productivity. This study aimed to investigate a synergistic amendment strategy for drought using the single and combined application of plant growth-promoting microorganisms (PGPM) (<i>Trichoderma harzianum</i>) and biogenic silica nanoparticles (SiO₂NPs) from rice husk ash (RHA) on Saudi Arabia's Spring wheat Summit cultivar (<i>Triticum aestivum</i> L.) for 102 DAS (days after sowing). The significant improvement was due to the application of 600 ppm SiO₂NPs and <i>T. harzianum</i> + 600 ppm SiO₂NPs, which enhanced the physiological properties of chlorophyll a, carotenoids, total pigments, osmolytes, and antioxidant contents of drought-stressed wheat plants as adaptive strategies. The results suggest that the expression of the studied genes (<i>TaP5CS1</i>, <i>TaZFP34</i>, <i>TaWRKY1</i>, <i>TaMPK3</i>, <i>TaLEA</i>, and the wheat housekeeping gene <i>TaActin</i>) in wheat remarkably enhanced wheat tolerance to drought stress. We discovered that the genes and metabolites involved significantly contributed to defense responses, making them potential targets for assessing drought tolerance levels. The drought tolerance indices of wheat were revealed by the mean productivity (MP), stress sensitivity index (SSI), yield stability index (YSI), and stress tolerance index (STI). We employed four databases, such as BAR, InterPro, phytozome, and the KEGG pathway, to predict and decipher the putative domains in prior gene sequencing. As a result, we discovered that these genes may be involved in a range of important biological functions in specific tissues at different developmental stages, including response to drought stress, proline accumulation, plant growth and development, and defense response. In conclusion, the sole and/or dual <i>T. harzianum</i> application to the wheat cultivar improved drought tolerance strength. These findings could be insightful data for wheat production in Saudi Arabia under various water regimes.