Auxin controls multiple aspects of plant growth and development. However, its role in stress responses remains poorly understood. Auxin acts on the transcriptional regulation of target genes, mainly through Auxin Response Factors (ARF). This study focuses on the involvement of SlARF4 in tomato tolerance to salinity and osmotic stress. Using a reverse genetic approach, we found that the antisense down-regulation of SlARF4 promotes root development and density, increases soluble sugars content and maintains chlorophyll content at high levels under stress conditions. Furthermore, ARF4-as displayed higher tolerance to salt and osmotic stress through reduced stomatal conductance coupled with increased leaf relative water content and Abscisic acid (ABA) content under normal and stressful conditions. This increase in ABA content was correlated with the activation of ABA biosynthesis genes and the repression of ABA catabolism genes. Cu/ZnSOD and mdhar genes were up-regulated in ARF4-as plants which can result in a better tolerance to salt and osmotic stress. A CRISPR/Cas9 induced SlARF4 mutant showed similar growth and stomatal responses as ARF4-as plants, which suggest that arf4-cr can tolerate salt and osmotic stresses. Our data support the involvement of ARF4 as a key factor in tomato tolerance to salt and osmotic stresses and confirm the use of CRISPR technology as an efficient tool for functional reverse genetics studies.

Water availability is the main factor that explains current patterns of palm abundance. However, the interaction between water stress and increasing atmospheric CO 2 concentrations caused by climatic change and its effects on palm physiology remain poorly known. Macauba palm is a widespread Neotropical species commonly found in ecosystems subjected to seasonal drought and has potential use in oil production. The present work investigated the influence of increased CO 2 concentrations on photosynthetic responses to drought in macauba palm plants. Exposure to increased CO 2 concentrations led to up-regulation of photosynthesis through higher stomatal conductance and improved light and water use efficiency. Macauba palm plants under water stress, irrespective of CO 2 concentration, were able to maintain constant levels of proline and chlorophyll, while preventing oxidative damage. Plants grown at higher CO 2 concentrations were more capable of recovering from drought due to higher Rubisco carboxylation rate (Vc max) and electron transport rate (J max), which prevented a reduction in total dry mass at the end of the stress period. Stomatal control of photosynthesis, coupled with the prevention of severe damage under stress, would allow efficient biomass production by the macauba palm under future scenarios of climate change.

Changes in atmospheric CO 2 levels are accompanied by ecological interactions involving other environmental factors, such as drought, which can severely alter the water balance of plants, thereby influencing sap flow, gas exchange, and plant growth. The objective of this study was to evaluate the water use economy, leaf gas exchange, and growth of young plants of the species Lafoensia pacari subjected to high concentrations of atmospheric CO 2 ([CO 2 ]) and soil water deficit. Increased vapor pressure deficit was observed from 1200 to 1800 hours. Plants under elevated [CO 2 ] exhibited increased leaf photosynthesis, resulting in improved growth. Specific leaf area was lower in plants under high [CO 2 ], mainly after soil water deficit treatment. Daily irrigated plants growing under ambient [CO 2 ] had higher stem sap flow velocity (cm h-1) and hourly sap flow (kg h-1), mainly during the hottest hours of the day, than plants under high [CO 2 ]. Improved water use by plants growing under high [CO 2 ] may result in increased availability of water in the soil, partially offsetting future drought events and extending the growth period.

Fire is an abiotic disturbance that regulates vegetation structure and biodiversity. Some plant species have adapted to fi re prone environments by evolving protective structures. Acrocomia aculeata (macaw palm) is widely distributed throughout tropical America, and is found in environments continuously infl uenced by anthropogenic fi re. We aimed to determine whether the fruit characteristics of A. aculeata enable seeds to resist the eff ects of fi re and also the consequent eff ects of fi re on fruit biometric traits and embryo viability. After a fi re event in a region of pastureforest transition, we marked 30 individuals of A. aculeata. Th e trees were separated by UPGMA analysis into 5 groups according to fi re exposure, ranging from trees with no exposure to trees with fruit completely exposed to fi re. Fruit exposure to high temperatures led to lower values in fruit fresh weight, length, density, and processable mass.Fire had no signifi cant eff ect on seed biometric variables, because of the structures of the fruit, including its lignifi ed endocarp and its insulating and mucilaginous mesocarp. Th ese structures helped to maintain the embryos viability by preventing oxidative damage. In conclusion, the fruit structure of the macaw palm may facilitate seed persistence, even when subject to increasingly frequent fi re events.

1ARF4-as plants displayed a leaf curl phenotype, a low stomatal conductance coupled with an 2 2 increase in leaf relative water content and ABA content under normal and stressful conditions. 3This increase in ABA content was correlated with the activation of ABA biosynthesis genes 2 4 and the repression of ABA catabolism genes. cat1, Cu/ZnSOD and mdhar genes were up-2 5 regulated in ARF4-as plants suggesting that ARF4-as mutant is more tolerant to salt and water 2 6 stress.The data presented in this work strongly support the involvement of ARF4 as a key 2 7 actor in tomato tolerance to salt and drought stresses. 2 8