Title : Trichoderma spp. effects on gene expression in two tomato genotypes Ailsa Craig and its ABA-deficient mutant flacca in short term water deficit
Abstract:
This study aimed to investigate the short-term effects of T. harzianum and T. brevicompactum on the expression of several defense- and metabolism-related genes in tomato leaves during a 48-hour drought cycle. Plants were grown in pots under controlled conditions in a growth chamber and subjected to six treatments: optimal water supply (soil volumetric water content: 37%), cessation of watering, and the same conditions with T. harzianum or T. brevicompactum inoculation (8 × 10? CFU). Trichoderma was applied near the root at the four fully developed leaf stage. Two tomato genotypes, the wild type (Ailsa Craig) and its ABA-deficient mutant flacca, were analyzed to elucidate ABA’s role in transcriptional responses to drought and Trichoderma. The expression of PINII (jasmonic acid-related), FLS (flavonoid-related), SlJAF13 (anthocyanin-related), TPX1 (lignin- and suberin-related), and C3H (caffeic and chlorogenic acid-related), as well as NCED2 (ABA-related), were examined using quantitative reverse transcription real-time polymerase chain reaction (qRT-PCR). Soil water content (SWC, Theta Probe), chlorophyll content, and epidermal flavonol content (Dualex Scientific sensor) were measured 4, 24, and 48 hours after treatment initiation. The highest PINII activation was observed in flacca mutants under drought with T. harzianum, whereas in the wild type, the highest expression was detected in well-watered plants treated with the same strain, indicating enhanced resistance to biotic stress. The upregulation of SlJAF13 and FLS genes in both tomato genotypes suggests that both Trichoderma strains contribute to anthocyanin and flavonol accumulation, enhancing antioxidant protection and plant resilience to abiotic stress. The upregulation of the TPX1 gene in flacca mutants indicates an adaptive response to increased stomatal openness, which may lead to excessive water loss. Increased TPX1 expression enhanced lignin and suberin accumulation in leaf cell walls, potentially indicating a protective response to reduce water loss, particularly under drought with Trichoderma treatment. The expected increase in NCED2 gene expression was detected under drought conditions. However, a reduction was observed in optimally watered flacca plants treated with both Trichoderma strains and in drought-stressed plants treated with T. brevicompactum, indicating a decreased requirement for ABA and potentially improved osmoregulation and water uptake. The observed downregulation of the C3H gene under drought in ABA-deficient mutants aligns with their reduced potential for flavonol and phenolic synthesis. However, TPX1 was upregulated, likely due to increased ROS accumulation. In T. harzianum treatment, PINII was highly upregulated, indicating activation of the JA pathway in ABA-deficient mutants. The general upregulation of FLS by T. brevicompactum under all conditions suggests the presence of ABA-independent ROS scavenging mechanisms.
