Davide Lucien Patono

The DOWNY MILDEW RESISTANCE 6 (DMR6) protein is a 2-oxoglutarate (2OG) and Fe(II)-dependent oxygenase, involved in salicylic acid (SA) metabolism, and its inactivation in tomato was found to increase SA levels and to confer disease-resistance against several pathogens. SA is also recognized as an abiotic stress-tolerance enhancer, and we tested the resistance to drought stress in Sldmr6-1 tomato mutants generated by the CRISPR/Cas9 technique. Wild-type (WT) tomato cultivar ‘San Marzano’ and its Sldmr6-1 mutants were subjected to water deprivation for 7 days. At the end of the period, while WT plants exhibited severe wilting, the T ₂ Sldmr6-1 mutant plants showed turgid leaves and maintained higher Soil Relative Water Content (SRWC). Sldmr6-1 mutants adopted a water saving behaviour reducing transpiration rate (E) by decreasing stomatal conductance (Gs). Assimilation rate (A) decreased in parallel to E under drought stress, resulting in no alteration of the CO ₂ concentration in the sub-stomatal chamber (Ci) and increasing the Water Use Efficiency (WUE, A/E). Defence mechanisms of the photosynthetic machinery triggered in Sldmr6-1 mutants, that under drought stress showed up-regulation of the genes SlAPX and SlGST (anti-oxidant related) as well as down-regulation of SlCYP707A2 gene, which is involved in ABA catabolism. Our results suggest that the disabling of SlDMR6-1 in tomato plants leads to a drought-avoidance strategy through tight control of stomatal closure controlling water loss. In addition, it was highlighted, for the first time in tomato, that Sldmr6-1 mutants showed reduced susceptibility to Phytophthora infestans , the causal agent of Late Blight.

Summary: Coffee is one of the most traded commodities world‐wide. As with 70% of land plants, coffee is associated with arbuscular mycorrhizal (AM) fungi, but the molecular bases of this interaction are unknown. We studied the mycorrhizal phenotype of two commercially important Coffea arabica cultivars (‘Typica National’ and ‘Catimor Amarillo’), upon Funnelliformis mosseae colonisation grown under phosphorus limitation, using an integrated functional approach based on multi‐omics, physiology and biochemistry. The two cultivars revealed a strong biomass increase upon mycorrhization, even at low level of fungal colonisation, improving photosynthetic efficiency and plant nutrition. The more important iconic markers of AM symbiosis were activated: We detected two gene copies of AM‐inducible phosphate (Pt4), ammonium (AM2) and nitrate (NPF4.5) transporters, which were identified as belonging to the C. arabica parental species (C. canephora and C. eugenioides) with both copies being upregulated. Transcriptomics data were confirmed by ions and metabolomics analyses, which highlighted an increased amount of glucose, fructose and flavonoid glycosides. In conclusion, both coffee cultivars revealed a high responsiveness to the AM fungus along their root‐shoot axis, showing a clear‐cut re‐organisation of the major metabolic pathways, which involve nutrient acquisition, carbon fixation, and primary and secondary metabolism.

SUMMARY: To understand how grapevine sinks compete with each other during water stress and subsequent rehydration, carbon (C) allocation patterns in drought‐rehydrated vines (REC) at the beginning of fruit ripening were compared with control vines maintained under drought (WS) or fully irrigated (WW). In the 30 days following rehydration, the quantity and distribution of newly fixed C between leaves, roots and fruits was evaluated through ¹³CO₂ pulse‐labeling and stable isotope ratio mass spectrometry. REC plants diverted the same percentage of fixed C towards the berries as the WS plants, although the percentage was higher than that of WW plants. Net photosynthesis (measured simultaneously with root respiration in a multichamber system for analysis of gas exchange above‐ and below‐ground) was approximately two‐fold greater in REC compared to WS treatment, and comparable or even higher than in WW plants. Maximizing C assimilation and delivery in REC plants led to a significantly higher amount of newly fixed C compared to both control treatments, already 2 days after rehydration in root, and 2 days later in the berries, in line with the expression of genes responsible for sugar metabolism. In REC plants, the increase in C assimilation was able to support the requests of the sinks during fruit ripening, without affecting the reserves, as was the case in WS. These mechanisms clarify what is experienced in fruit crops, when occasional rain or irrigation events are more effective in determining sugar delivery towards fruits, rather than constant and satisfactory water availabilities.