Plant science decadal vision 2020-2030: Reimagining the potential of plants for a healthy and sustainable future.

Plants, and the biological systems around them, are key to the future health of the planet and its inhabitants. The Plant Science Decadal Vision 2020-2030 frames our ability to perform vital and far-reaching research in plant systems sciences, essential to how we value participants and apply emerging technologies. We outline a comprehensive vision for addressing some of our most pressing global problems through discovery, practical applications, and education. The Decadal Vision was developed by the participants at the Plant Summit 2019, a community event organized by the Plant Science Research Network. The Decadal Vision describes a holistic vision for the next decade of plant science that blends recommendations for research, people, and technology. Going beyond discoveries and applications, we, the plant science community, must implement bold, innovative changes to research cultures and training paradigms in this era of automation, virtualization, and the looming shadow of climate change. Our vision and hopes for the next decade are encapsulated in the phrase reimagining the potential of plants for a healthy and sustainable future. The Decadal Vision recognizes the vital intersection of human and scientific elements and demands an integrated implementation of strategies for research (Goals 1-4), people (Goals 5 and 6), and technology (Goals 7 and 8). This report is intended to help inspire and guide the research community, scientific societies, federal funding agencies, private philanthropies, corporations, educators, entrepreneurs, and early career researchers over the next 10 years. The research encompass experimental and computational approaches to understanding and predicting ecosystem behavior; novel production systems for food, feed, and fiber with greater crop diversity, efficiency, productivity, and resilience that improve ecosystem health; approaches to realize the potential for advances in nutrition, discovery and engineering of plant-based medicines, and "green infrastructure." Launching the Transparent Plant will use experimental and computational approaches to break down the phytobiome into a "parts store" that supports tinkering and supports query, prediction, and rapid-response problem solving. Equity, diversity, and inclusion are indispensable cornerstones of realizing our vision. We make recommendations around funding and systems that support customized professional development. Plant systems are frequently taken for granted therefore we make recommendations to improve plant awareness and community science programs to increase understanding of scientific research. We prioritize emerging technologies, focusing on non-invasive imaging, sensors, and plug-and-play portable lab technologies, coupled with enabling computational advances. Plant systems science will benefit from data management and future advances in automation, machine learning, natural language processing, and artificial intelligence-assisted data integration, pattern identification, and decision making. Implementation of this vision will transform plant systems science and ripple outwards through society and across the globe. Beyond deepening our biological understanding, we envision entirely new applications. We further anticipate a wave of diversification of plant systems practitioners while stimulating community engagement, underpinning increasing entrepreneurship. This surge of engagement and knowledge will help satisfy and stoke people's natural curiosity about the future, and their desire to prepare for it, as they seek fuller information about food, health, climate and ecological systems.

The Development of Crassulacean Acid Metabolism (CAM) Photosynthesis in Cotyledons of the C4 Species, Portulaca grandiflora (Portulacaceae).

Portulaca grandiflora simultaneously utilizes both the C4 and Crassulacean acid metabolism (CAM) photosynthetic pathways. Our goal was to determine whether CAM developed and was functional simultaneously with the C4 pathway in cotyledons of P. grandiflora. We studied during development whether CAM would be induced with water stress by monitoring the enzyme activity, leaf structure, JO2 (rate of O2 evolution calculated by fluorescence analysis), and the changes in titratable acidity of 10 and 25 days old cotyledons. In the 10 days old cotyledons, C4 and CAM anatomy were evident within the leaf tissue. The cotyledons showed high titratable acid levels but a small CAM induction. In the 25 days old cotyledons, there was a significant acid fluctuation under 7 days of water stress. The overall enzyme activity was reduced in the 10 days old plants, while in the 25 days old plants CAM activity increased under water-stressed conditions. In addition to CAM, the research showed the presence of glycine decarboxylase in the CAM tissue. Thus, it appears both pathways develop simultaneously in the cotyledons but the CAM pathway, due to anatomical constraints, may be slower to develop than the C4 pathway. Cotyledons showed the ancestral Atriplicoid leaf anatomy, which leads to the question: Could a CAM cell be the precursor to the C4 pathway? Further study of this may lead to understanding into the evolution of C4 photosynthesis in the Portulaca.

Crassulacean acid metabolism as a continuous trait: variability in the contribution of Crassulacean acid metabolism (CAM) in populations of Portulacaria afra.

Portulacaria afra L. is a dominant facultative CAM species growing in the Southeastern Cape of South Africa. P. afra is well adapted to regions of the Spekboom thicket in areas of limited and sporadic rainfall. P. afra populations occur in isolated drainages. We hypothesized the utilization of CAM would vary in the different populations in response to rainfall and temperature gradients. Carbon isotope composition can be used to determine the contribution of CAM in leaf tissue. P. afra leaves of populations were analyzed in transects running south to north and east to west in locations from the coast to elevations of 1400 m. Carbon isotope values ranged from -16.1‰ in Plutosvale to -21.0‰ to -22.7‰ in Port Alfred and Grahamstown populations respectively with some values reaching -25.2‰. These values indicated an estimated variable contribution of the CAM pathway ranging from 23% to almost 60%. The results indicate a much greater range of variability than previously reported. The carbon isotope values showed no direct correlation with rainfall or maximum or minimum day/night temperatures in the summer or winter for the different locations. The results indicated the microclimate may play a more significant role in determining CAM utilization. We present evidence that CAM is a continuous trait in P. afra and CAM is operating continuously at low levels during C3 photosynthesis which may explain the high variability in its carbon isotope composition. P. afra populations illustrate a large phenotypic plasticity and further studies may indicate genotypic differences between populations. This may be valuable in ascertaining the genetic contribution to its water use efficiency and possible use in engineering higher water use efficiency in C3 plants. The results revealed here may explain P. afra's ability to sequester carbon at high rates compared to more mesic species.

Evolutionary physiology: the extent of C4 and CAM photosynthesis in the genera Anacampseros and Grahamia of the Portulacaceae.

The Portulacaceae is one of the few terrestrial plant families known to have both C(4) and Crassulacean acid metabolism (CAM) species. There may be multiple origins of the evolution of CAM within the Portulacaceae but the only clear evidence of C(4) photosynthesis is found in members of the genus Portulaca. In the Portulaca, CAM succulent tissue is overlaid with the C(4) tissue in a unique fashion where both pathways are operating simultaneously. Earlier reports have shown that the clade containing the genera Anacampseros and Grahamia may also contain C(4) photosynthetic species similar to the Portulaca, which would indicate multiple origins of C(4) photosynthesis within the family. The aim of the present study was to ascertain the true photosynthetic nature of these genera. An initial survey of the carbon isotope composition of the Anacampseros ranged from -12.6 per thousand to -24.0 per thousand, indicating very little CAM activity in some species, with other values close to the C(4) range. Anacampseros (=Grahamia) australiana which had been previously identified as a C(4) species had a carbon isotope composition value of -24.0 per thousand, which is more indicative of a C(3) species with a slight contribution of CAM activity. Other Anacampseros species with C(4)-like values have been shown to be CAM plants. The initial isotope analysis of the Grahamia species gave values in the range of -27.1 per thousand to -23.6 per thousand, placing the Grahamia species well towards the C(3) photosynthetic range. Further physiological studies indicated increased night-time CO(2) uptake with imposition of water stress, associated with a large diurnal acid fluctuation and a marked increased phosphoenolpyruvate carboxylase activity. This showed that the Grahamia species are actually facultative CAM plants despite their C(3)-like carbon isotope values. The results indicate that the Grahamia and Anacampseros species do not utilize the C(4) photosynthetic pathway. This is the first to identify that the Grahamia species are facultative CAM plants where CAM can be induced by water stress. This work supports earlier physiological work that indicates that this clade containing Anacampseros and Grahamia species comprises predominantly facultative CAM plants. This report suggests there may be only one clade which contains C(4) photosynthetic members with CAM-like characteristics.

Photosynthetic and anatomical characteristics in the C4crassulacean acid metabolism-cycling plant Portulaca grandiflora.

This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001. Portulaca grandiflora (Lind.) is a succulent species with C4 photosynthesis and crassulacean acid metabolism (CAM) cycling in leaves, and CAM-idling type photosynthesis in stems. We investigated the level and localization of carbon fixation enzymes and photosynthetic activity of leaves and stems of P. grandiflora under well-watered and drought conditions. As CAM activity increased during water stress, the leaf water-storage tissue collapsed, presumably transferring water to the bundle sheath and mesophyll cells, and so maintaining the C4 photosynthetic pathway. Tissue prints indicated an increase in phosphoenolpyruvate carboxylase (PEPC) in the water-storage tissue of leaves and the cortex of stems. Immunoblot analyses after 10 d of water stress showed that leaves had a slight decrease in the proteins of the C4-CAM pathway, while at the same time a new isoform of NADP-malic enzyme (NADP-ME) appeared. In contrast, the stem showed increases in proteins of the CAM pathway when water stressed. Under water stress, diurnal fluctuation in acidity in leaves was not accompanied by a net gain or loss of CO2 at night, and there was sustained, but decreased, fixation of CO2 during the day, characteristic of CAM cycling. High gross rates of O2 evolution were maintained during the day under water stress, suggesting induction of alternative electron sinks. With induced diurnal fluctuations in acidity in stems, there was no net carbon gain during the day or night. These results demonstrate, for the first time, that the stem of P. grandiflora is an inducible CAM-idling tissue. Our results also indicate that the C4 and CAM pathways operate independently of one another in P. grandiflora.

Seasonal response to drought and rewatering in Portulacaria afra (L.) Jacq.

Gas exchange characteristics of droughted and rewatered Portulacaria afra were studied during the seasonal shift from CAM to C3 photosynthesis. 14CO2 uptake, stomatal conductance, and total titratable acidity were determined for both irrigated and 2, 4, and 7.5 month waterstressed plants from summer 1984 to summer 1985. Irrigated P. afra plants were utilizing the CAM pathway throughout the summer and shifted to C3 during the winter and spring. Beginning in September, P. afra plants shifted from CAM to CAM-idling after 2 months of water-stress. When water-stress was initiated later in the fall, exogenous CO2 uptake was still measurable after 4 months of drought. After 7.5 months of stress, exogenous CO2 uptake was absent. The shift from CAM to CAM-idling or C3 in the fall and winter was related to when water stress was initiated and not to the duration of the stress. Gas exchange resumed within 24 h of rewatering regardless of the duration of the drought. In the winter and spring, rewatering resulted in a full resumption of daytime CO2 uptake. Whereas during the summer, rewatering quickly resulted in early morning CO2 uptake, but nocturnal CO2 uptake through the CAM pathway was observed after 7 days. Gas exchange measurements, rewatering characteristics, and transpirational water loss support the hypothesis that the C3 pathway was favored during the winter and spring. The CAM pathway was functional during the summer when potential for water loss was greater. Our investigations indicate that P. afra has a flexible photosynthetic system that can withstand long-term drought and has a rapid response to rewatering.