A Preliminary Study of Crassulacean Acid Metabolism (CAM) in the Endangered Aquatic Quillwort Isoetes sinensis Palmer in China

Isoetes sinensis Palmer (Isoetaceae) is an aquatic or amphibious plant that is critically endangered in China. Previous studies have revealed the crassulacean acid metabolism (CAM)-like photosynthetic pathway occurs commonly in submerged leaves in genusIsoetes. Water chemistry parameters and the titratable acidity content of the plant extract were measured from samples obtained in the early morning (7∶00) and late afternoon (15∶00) from twoI. sinensis populations in China. One population occurs in the eulittoral zone of a freshwater tidal river at low elevation (134 m) and another occurs in a densely vegetated, high elevation (1 100 m) alpine shallow pool. Significant differences in pH and titratable acidity of the plant extract were detected between the morning and afternoon samples. These changes are associated with diurnal changes in water chemistry. Our results provide the first evidence for the existence of the CAM pathway in the East Asian endemicIsoetes sinensis Palmer. The magnitude of fluctuations in the titratable acidity of the plant extract may be correlated with the severe carbon limitation imposed on the plants by its aquatic habitat.

Transcriptomic Analysis of Differentially Expressed Genes and Alternative Splicing Events Associated with Crassulacean Acid Metabolism in Orchids

Phalaenopsis equestris is an obligate crassulacean acid metabolism(CAM) plant with high ornamental and economic value. CAM photosynthesis is associated with drought tolerance and efficient water utilization, which enhances the survival rate of CAM plants in arid environments.The identification and analysis of CAM-related genes will be helpful to improve our understanding of the regulatory mechanisms of CAM metabolism. In this study, we analyzed RNA-Seq data to identify differentially expressed genes(DEGs) between circadian day and night in P.equestris leaves then performed GO and KEGG functional enrichment analysis. The pathways that were significantly enriched among these DEGs included carbon fixation, circadian clock regulation, glucose metabolism, photosynthesis, and plant hormone signaling. We also used Pac Bio long-read Iso-Seq technology, which identified many alternative splicing events for key genes in CAM-related pathways, including carbon fixation, circadian clock regulation, and stomatal movement. These findings suggested that alternative splicing events might be involved in CAM metabolism. Many unknown or uncharacterized genes were also found to be potentially involved in CAM metabolism. For example, the Peq000162 gene encodes a protein belonging to the Ldp A(light-dependent period) iron-sulfur protein family, and it was found to generate many alternatively spliced products. These findings shed light on CAM metabolic mechanisms in P. equestris along with the molecular functions of key CAM genes. Ultimately, the information may help enhance crop yield and drought tolerance through the introduction of CAM features into C3 crops.

Effect of Water Deficit Stress on Photosynthetic Characteristics of Jatropha curcas

The need to mitigate climate change cannot be more emphasized, which arises, as a result of increases in CO2 emissions due to anthropogenic activities. Given the current world energy problems of high fossil fuel consumption which plays a pivotal role in the greenhouse effect, Jatropha curcas biodiesel has been considered a potential alternative source of clean energy (biodiesel is carbon neutral). However, the ability of Jatropha curcas, as a candidate source of alternative of clean energy, to grow in marginal and dry soils, has been poorly elucidated. This study, therefore aimed at investigating whether Jatropha curcas leaves could switch from carrying out C3 photosynthetic pathway to Crassulacean Acid Metabolism (CAM) as a strategy to improve its water deficit tolerance. Thirty-five-day-old Jatropha curcas accessions, from three different climatic zones of Botswana, viz., Mmadinare (Central zone), Thamaga (Southern zone) and Maun (Northern zone), were subjected to water stress, by with-holding irrigation with half-strength Hoagland culture solution. Net photosynthetic rate, transpiration and stomatal conductance were measured at weekly intervals. The leaf pH was measured to determine whether there was a decrease in pH (leaf acidification) of the leaves during the night, when the plants experienced water deficit stress. All the accessions exhibited marked reduction in all the measured photosynthetic characteristics when experience water deficit stress. However, a measurable CO2 uptake was carried out by leaves of all the accessions, in the wake of marked decreases in stomatal conductance. There is evidence to suggest that when exposed to water stress J. curcas accessions switch from C3 mode of photosynthesis to CAM photosynthetic pathway. This is attested to by the slightly low leaf pH at night. Thamaga accession exhibited an earlier stomatal closure than the other two accessions. This resulted in Thamaga accession displaying a slightly lower dry weight than both Mmadinare and Maun accessions. It could be concluded that Jatropha curcas appeared to tolerate water deficit stress due to its ability of switching from C3 photosynthetic pathway to the CAM photosynthetic pathway, but with a cost to biomass accumulation, as demonstrated by slightly more reduced CO2 assimilation by Thamaga accession, than the other two accessions.

Diel dynamics of multi-omics in elkhorn fern provide new insights into weak CAM photosynthesis

Crassulacean acid metabolism(CAM)has high water-use efficiency(WUE)and is widely recognized to have evolved from C3 photosynthesis.Different plant lineages have convergently evolved CAM,but the molecular mechanism that underlies C3-to-CAM evolution remains to be clarified.Platycerium bifurcatum(elkhorn fern)provides an opportunity to study the molecular changes underlying the transition from C3 to CAM photosynthesis because both modes of photosynthesis occur in this species,with sporotrophophyll leaves(SLs)and cover leaves(CLs)performing C3 and weak CAM photosynthesis,respectively.Here,we report that the physiological and biochemical attributes of CAM in weak CAM-performing CLs differed from those in strong CAM species.We investigated the diel dynamics of the metabolome,proteome,and transcriptome in these dimorphic leaves within the same genetic background and under identical environmental conditions.We found that multi-omic diel dynamics in P.bifurcatum exhibit both tissue and diel effects.Our analysis revealed temporal rewiring of biochemistry relevant to the energy-producing pathway(TCA cycle),CAM pathway,and stomatal movement in CLs compared with SLs.We also confirmed that PHOSPHOENOLPYRUVATE CARBOXYLASE KINASE(PPCK)exhibits convergence in gene expression among highly divergent CAM lineages.Gene regulatory network analysis identified candidate transcription factors regulating the CAM pathway and stomatal movement.Taken together,our results provide new insights into weak CAM photosynthesis and new avenues for CAM bioengineering.

Genomic insights into the fast growth of paulownias and the formation of Paulownia witches' broom

Paulownias are among the fastest growing trees in the world,but they often suffer tremendous loss of wood production due to infection by Paulownia witches'broom(PaWB)phytoplasmas.In this study,we have sequenced and assembled a high-quality nuclear genome of Paulownia fortunei,a commonly cultivated paulownia species.The assembled genome of P.fortunei is 511.6 Mb in size,with 93.2%of its sequences anchored to 20 pseudo-chromosomes,and it contains 31985 protein-coding genes.Phylogenomic analyses show that the family Paulowniaceae is sister to a clade composed of Phrymaceae and Orobanchaceae.Higher photosynthetic efficiency is achieved by integrating C3 photosynthesis and the crassulacean acid metabolism pathway,which may contribute to the extremely fast growth habit of paulownia trees.Comparative transcriptome analyses reveal modules related to cambial growth and development,photosynthesis,and defense responses.Additional genome sequencing of PaWB phytoplasma,combined with functional analyses,indicates that the effector PaWB-SAP54 interacts directly with Paulownia PfSPLa,which in turn causes the degradation of PfSPLa by the ubiquitin-mediated pathway and leads to the formation of witches'broom.Taken together,these results provide significant insights into the biology of paulownias and the regulatory mechanism for the formation of PaWB.