Jasmonate (JA) signaling and functions have been established in rice development and response to a range of biotic or abiotic stress conditions. However, information on the molecular actors and mechanisms underlying turnover of the bioactive jasmonoyl-isoleucine (JA-Ile) is very limited in this plant species. Here we explored two gene families in rice in which some members were described previously in Arabidopsis to encode enzymes metabolizing JA-Ile hormone, namely cytochrome P450 of the CYP94 subfamily (CYP94, 20 members) and amidohydrolases (AH, 9 members). The CYP94D subclade, of unknown function, was most represented in the rice genome with about 10 genes. We used phylogeny and gene expression analysis to narrow the study to candidate members that could mediate JA-Ile catabolism upon leaf wounding used as mimic of insect chewing or seedling exposure to salt, two stresses triggering jasmonate metabolism and signaling. Both treatments induced specific transcriptional changes, along with accumulation of JA-Ile and a complex array of oxidized jasmonate catabolites, with some of these responses being abolished in the JASMONATE RESISTANT 1 (jar1) mutant. However, upon response to salt, a lower dependence on JAR1 was evidenced. Dynamics of CYP94B5, CYP94C2, CYP94C4 and AH7 transcripts matched best the accumulation of JA-Ile catabolites. To gain direct insight into JA-Ile metabolizing activities, recombinant expression of some selected genes was undertaken in yeast and bacteria. CYP94B5 was demonstrated to catalyze C12-hydroxylation of JA-Ile, whereas similarly to its Arabidopsis bi-functional homolog IAR3, AH8 performed cleavage of JA-Ile and auxin-alanine conjugates. Our data shed light on two rice gene families encoding enzymes related to hormone homeostasis. Expression data along with JA profiling and functional analysis identifies likely actors of JA-Ile catabolism in rice seedlings. This knowledge will now enable to better understand the metabolic fate of JA-Ile and engineer optimized JA signaling under stress conditions.

Biochar application is a promising sustainable strategy for enhancing soil properties thus crop production. However, biochar application to soil certainly alters its biological and physical properties, and could require extra costs. Therefore, biochar suitability to agroecosystems must be proactively estimated. The advantage of biochar addition to poor fertile or weathered soils has been well studies, however, its feasibility to fertile soil under low quality (saline) irrigation water was not frequently studied. Consequently, this work investigates the hypothesis of whether the application of biochar at a rate of 4.8 tons/ha to fertile soil (Nile Valley, Giza, Egypt) would ameliorate the negative effects of saline irrigation regime (3000 ppm) on tomato crop and soil. The results of two seasons experiments showed that saline irrigation significantly reduced tomato crop yield by an average reduction ratio of 51%, and biochar addition could not compensate such reduction. Furthermore, biochar did not reduce accumulated Na⁺ in fruits or roots. Tomato fruits produced from biochar-added soil were lower in TSS levels (41.7% reduction ratio) yet larger in diameter by approximately 1.5-fold increase. Interestingly, biochar addition into soil greatly promotes the length of stem-borne lateral roots and elevates the expression of LeNR (encodes nitrate reductase enzyme) in leaves yet under fresh irrigation regime. For soil properties, biochar application enhanced the soil properties under either saline or fresh water irrigation conditions. Collectively, it is assumed that biochar application to fertile soil in Nile Valley of Egypt could not alleviate tomato fruits yield reduction affected by applied saline irrigation regime.

Background: Climate change alters modern drought episode patterns by making them longer, more frequent and more severe, in particular in arid and semi-arid agroecosystems. Amending soil properties and enhancing its fertility is a needed sustainable strategy for mitigating drought’s damaging effects on crop production and food security. Here, we planned to investigate the potential benefits of biochar–compost mixture (B×C) as a biochar-based fertilizer (BCF) in enhancing the drought tolerance of rice plants cultivated in low-fertile sandy soil. Results: Under drought stress, rice plants cultivated in unamended soil (no B×C) exhibited severely wilted, rolled and discolored shoots. Furthermore, the shoot dry biomass reduction ratio was 73.3% compared to 44.2 and 27.6% for plants treated with 5 and 15% B×C, respectively. Root anatomical and architectural traits were significantly less impaired in B×C plants and reflected better performance under drought compared to no B×C plants. During the induced drought episode, soil moisture content was enhanced by 2.5-fold through adding B×C, compared to unamended soil, thereby reducing the negative impact of drought stress. Moreover, the less drought-stressed rice plants (B×C-treated) rapidly recovered after rewatering and displayed the unwinding of previously rolled leaves and reproduced panicles. On the other hand, no B×C plants failed to recover and eventually perished completely. The expression profiles of several drought responsive genes suggest that leaves of more stressed rice plants (no B×C) significantly accumulated more cytosolic free calcium (OsCML3) and apoplastic H₂O₂ (OsOXO4) which eventually may trigger fast and prolonged stomatal closure (OsSRO1c). In addition, more drought-stressed plants (no B×C) may over-produce the reactive oxygen species (ROS) superoxide anion molecules (OsRbohB), the negative situation that has been further complicated by a possible reduction in the activity of the antioxidative enzyme SOD (OsSOD), and thus more lipid peroxidation (3.5-fold increase MDA) in drought-stressed (no B×C) plant shoots compared to B×C plants. Conclusion: It is suggested that soil amendment B×C (biochar–compost mixture) could promote drought stress tolerance in rice plants by retaining more soil moisture content, thereby mitigating the negative effects of drought stress, such as the over-production of ROS in leaves, and thus eventually facilitating recovery after rewatering.

Background: Real-time PCR system is a valuable scientific mainstream needed for quantifying specific gene expression. Nevertheless, compared with conventional PCR, the real-time PCR system is extremely expensive and not affordable for limited or mid-budget research laboratories. Here, a novel, doable and low-cost recipe (referred to as gel express) is developed to quantify gene expression using conventional RT-PCR assay. The novelty of the gel express method is based on replacing crossing point (CP) values with integrated density (IntDen) values of PCR amplicon bands in real-time PCR regular mathematical formulas. Results: In this work, gene expression profiles of two different rice stress-marker genes (OsCYP94C2a and OsLOX8) were quantified in response to mechanical wounding at different time points (0, 30, 60, and 150 min). In the gel express method, the free software ImageJ was employed to measure integrated density (IntDen) values of PCR amplicon bands in agarose gel images. IntDen values were then used instead of crossing point (CP) values according to the following modified formula: [E^IntDen(ref)/E^{IntDen(target)}]_sample ÷ [E^IntDen(ref)/E^{IntDen(target)}]_control. Gene relative expression profiles (dynamic expression pattern) quantified by gel express method in both genes were highly comparable with real-time RT-PCR. R² values were 0.9976 and 0.9975 in OsCYP94C2a and OsLOX, respectively. PCR amplification efficiency (E) for all studied genes could be calculated depending on IntDen values through experimentally designed calibration curves. PCR amplification efficiencies with all studied genes obtained by gel express were all in the accepted range. For better-visualized PCR amplicons thus detectable biological effects between treatments, the number of PCR cycles applied in gel express method (IntCyc) was experimentally estimated to be 29 cycles. Conclusions: Gel express is a novel, cost-effective and feasible recipe for quantifying gene relative expression in conventional RT-PCR. The expression pattern quantified by gel express is highly comparable and fits the expression data revealed by the used real-time PCR system.