Crassulacean acid metabolism (CAM) is a water-use efficient adaptation of photosynthesis that has evolved independently many times in diverse lineages of flowering plants. We hypothesize that convergent evolution of protein sequence and temporal gene expression underpins the independent emergences of CAM from C₃ photosynthesis. To test this hypothesis, we generate a de novo genome assembly and genome-wide transcript expression data for Kalanchoë fedtschenkoi, an obligate CAM species within the core eudicots with a relatively small genome (~260 Mb). Our comparative analyses identify signatures of convergence in protein sequence and re-scheduling of diel transcript expression of genes involved in nocturnal CO₂ fixation, stomatal movement, heat tolerance, circadian clock, and carbohydrate metabolism in K. fedtschenkoi and other CAM species in comparison with non-CAM species. These findings provide new insights into molecular convergence and building blocks of CAM and will facilitate CAM-into-C₃ photosynthesis engineering to enhance water-use efficiency in crops.

Salt stress is one of the major environmental stresses in agriculture worldwide and affects crop productivity and quality. The development of crops with elevated levels of salt tolerance is therefore highly desirable. In the present study, a novel maspardin gene, named IbMas, was isolated from salt-tolerant sweetpotato (Ipomoea batatas (L.) Lam.) line ND98. IbMas contains maspardin domain and belongs to α/β-hydrolase superfamily. Expression of IbMas was up-regulated in sweetpotato under salt stress and ABA treatment. The IbMas-overexpressing sweetpotato (cv. Shangshu 19) plants exhibited significantly higher salt tolerance compared with the wild-type. Proline content was significantly increased, whereas malonaldehyde content was significantly decreased in the transgenic plants. The activities of superoxide dismutase (SOD) and photosynthesis were significantly enhanced in the transgenic plants. H₂O₂ was also found to be significantly less accumulated in the transgenic plants than in the wild-type. Overexpression of IbMas up-regulated the salt stress responsive genes, including pyrroline-5-carboxylate synthase, pyrroline-5-carboxylate reductase, SOD, psbA and phosphoribulokinase genes, under salt stress. These findings suggest that overexpression of IbMas enhances salt tolerance of the transgenic sweetpotato plants by regulating osmotic balance, protecting membrane integrity and photosynthesis and increasing reactive oxygen species scavenging capacity.

ζ-Carotene desaturase (ZDS) is one of the key enzymes in carotenoid biosynthesis pathway. However, the ZDS gene has not been applied to carotenoid improvement of plants. Its roles in tolerance to abiotic stresses have not been reported. In this study, the IbZDS gene was isolated from storage roots of sweetpotato (Ipomoea batatas (L.) Lam.) cv. Nongdafu 14. Its overexpression significantly increased β-carotene and lutein contents and enhanced salt tolerance in transgenic sweetpotato (cv. Kokei No. 14) plants. Significant up-regulation of lycopene β-cyclase (β-LCY) and β-carotene hydroxylase (β-CHY) genes and significant down-regulation of lycopene ε-cyclase (ε-LCY) and ε-carotene hydroxylase (ε-CHY) genes were found in the transgenic plants. Abscisic acid (ABA) and proline contents and superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were significantly increased, whereas malonaldehyde (MDA) content was significantly decreased in the transgenic plants under salt stress. The salt stress-responsive genes encoding pyrroline-5-carboxylate reductase (P5CR), SOD, CAT, ascorbate peroxidase (APX) and POD were found to be significantly up-regulated in the transgenic plants under salt stress. This study indicates that the IbZDS gene has the potential to be applied for improving β-carotene and lutein contents and salt tolerance in sweetpotato and other plants.

Non-coding RNAs (ncRNAs), that is, RNAs not translated into proteins, are crucial regulators of a variety of biological processes in plants. While protein-encoding genes have been relatively well-annotated in sequenced genomes, accounting for a small portion of the genome space in plants, the universe of plant ncRNAs is rapidly expanding. Recent advances in experimental and computational technologies have generated a great momentum for discovery and functional characterization of ncRNAs. Here we summarize the classification and known biological functions of plant ncRNAs, review the application of next-generation sequencing (NGS) technology and ribosome profiling technology to ncRNA discovery in horticultural plants and discuss the application of new technologies, especially the new genome-editing tool clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (Cas9) systems, to functional characterization of plant ncRNAs.