The role of starch in the day/night re-programming of stomata in plants with Crassulacean Acid Metabolism

Ph. D. ThesisCrassulacean acid metabolism (CAM) is a specialised type of photosynthesis characterised by the unique inverted stomatal rhythm, which increases water use efficiency (WUE) and enhances the potential for sustainable biomass production in warmer and drier conditions. Starch turnover in the mesophyll of CAM species supports nocturnal CO2 assimilation and CAM activity. In C3 plants, starch metabolism has been reported to play an important role in determining stomatal behaviour; in this case, guard cell starch degradation is triggered by blue light, producing osmolytes that promotes stomatal opening. Based on the importance of starch and the little knowledge regarding CAM stomatal behaviour, this study tested the hypothesis that starch metabolism has been re-programmed in CAM plants to enable nocturnal stomatal opening, by using biochemical and genetic characterisation of wild type and RNAi lines with curtailed starch metabolism in the constitutive CAM species Kalanchoë fedtschenkoi. Measurements of guard cell starch content over 24 hours in wild type plants of K. fedtschenkoi indicated a day/night shift in starch turnover compared to C3, evidenced by an increment over the first hours of the day and a diminution at the beginning of the night. The characterisation of the RNAi lines confirmed that curtailed starch metabolism affected nocturnal CO2 fixation, besides the phosphorolytic starch degradation has a pivotal role for driving nocturnal CAM activity evidenced, in the same way, in both mesophyll and epidermis proteome datasets. Furthermore, higher levels of soluble sugars in the epidermis of the RNAi lines appeared to curtail completely stomatal closure during the day, indicating that guard cell starch biosynthesis is an important sink for carbohydrates, ensuring day-time stomatal closure. Finally, this thesis constituted an approach for the understanding of starch metabolism in CAM stomata and together with further studies lead to the potential engineering of CAM into C3 to enhance WUE.Government of Colombia through the Administrative Department of Science, Technology and Innovation – Colciencias and the Newton-Caldas fund partnership

The starch-deficient plastidic PHOSPHOGLUCOMUTASE mutant of the constitutive crassulacean acid metabolism (CAM) species Kalanchoë fedtschenkoi impacts diel regulation and timing of stomatal CO2 responsiveness.

Background and aimsCrassulacean acid metabolism (CAM) is a specialised type of photosynthesis characterised by a diel pattern of stomatal opening at night and closure during the day, which increases water-use efficiency. Starch degradation is a key regulator of CAM, providing phosphoenolpyruvate as substrate in the mesophyll for nocturnal assimilation of CO2. Growing recognition of a key role for starch degradation in C3 photosynthesis guard cells for mediating day-time stomatal opening presents the possibility that starch degradation might also impact CAM by regulating the provision of energy and osmolytes to increase guard cell turgor and drive stomatal opening at night. This study tested the hypothesis that the timing of diel starch turnover in CAM guard cells has been re-programmed during evolution to enable nocturnal stomatal opening and day-time closure.MethodsBiochemical and genetic characterisation of wild type and starch-deficient RNAi lines of Kalanchoë fedtschenkoi with reduced activity of plastidic phosphoglucomutase (PGM) constituted a preliminary approach for the understanding of starch metabolism and its implications for stomatal regulation in CAM plants.Key resultsStarch deficiency reduced nocturnal net CO2 uptake, but had negligible impact on nocturnal stomatal opening. In contrast, day-time stomatal closure was reduced in magnitude and duration in the starch-deficient rPGM RNAi lines, and their stomata were unable to remain closed in response to elevated concentrations of atmospheric CO2 administered during the day. Curtailed day-time stomatal closure was linked to higher soluble sugar contents in the epidermis and mesophyll.ConclusionsNocturnal stomatal opening is not reliant upon starch degradation, but starch biosynthesis is an important sink for carbohydrates, ensuring day-time stomatal closure in this CAM species

Undervalued potential of crassulacean acid metabolism for current and future agricultural production

The potential for crassulacean acid metabolism (CAM) to support resilient crops that meet demands for food, fiber, fuel, and pharmaceutical products far exceeds current production levels. This review provides background on five families of plants that express CAM, including examples of many species within these families that have potential agricultural uses. We summarize traditional uses, current developments, management practices, environmental tolerance ranges, and economic values of CAM species with potential commercial applications. The primary benefit of CAM in agriculture is high water use efficiency that allows for reliable crop yields even in drought conditions. Agave species, for example, grow in arid conditions and have been exploited for agricultural products in North and South America for centuries. Yet, there has been very little investment in agricultural improvement for most useful Agave varieties. Other CAM species that are already traded globally include Ananas comosus (pineapple), Aloe spp., Vanilla spp., and Opuntia spp., but there are far more with agronomic uses that are less well known and not yet developed commercially. Recent advances in technology and genomic resources provide tools to understand and realize the tremendous potential for using CAM crops to produce climate-resilient agricultural commodities in the future.</p

Clinical Heterogeneity and Different Phenotypes in Patients with <i>SETD2</i> Variants: 18 New Patients and Review of the Literature

SETD2 belongs to the family of histone methyltransferase proteins and has been associated with three nosologically distinct entities with different clinical and molecular features: Luscan–Lumish syndrome (LLS), intellectual developmental disorder, autosomal dominant 70 (MRD70), and Rabin–Pappas syndrome (RAPAS). LLS [MIM #616831] is an overgrowth disorder with multisystem involvement including intellectual disability, speech delay, autism spectrum disorder (ASD), macrocephaly, tall stature, and motor delay. RAPAS [MIM #6201551] is a recently reported multisystemic disorder characterized by severely impaired global and intellectual development, hypotonia, feeding difficulties with failure to thrive, microcephaly, and dysmorphic facial features. Other neurologic findings may include seizures, hearing loss, ophthalmologic defects, and brain imaging abnormalities. There is variable involvement of other organ systems, including skeletal, genitourinary, cardiac, and potentially endocrine. Three patients who carried the missense variant p.Arg1740Gln in SETD2 were reported with a moderately impaired intellectual disability, speech difficulties, and behavioral abnormalities. More variable findings included hypotonia and dysmorphic features. Due to the differences with the two previous phenotypes, this association was then named intellectual developmental disorder, autosomal dominant 70 [MIM 620157]. These three disorders seem to be allelic and are caused either by loss-of-function, gain-of-function, or missense variants in the SETD2 gene. Here we describe 18 new patients with variants in SETD2, most of them with the LLS phenotype, and reviewed 33 additional patients with variants in SETD2 that have been previously reported in the scientific literature. This article offers an expansion of the number of reported individuals with LLS and highlights the clinical features and the similarities and differences among the three phenotypes associated with SETD2