The Kalanchoë genome provides insights into convergent evolution and building blocks of crassulacean acid metabolism.

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.

Key KdSOC1 gene expression profiles during plantlet morphogenesis under hormone, photoperiod, and drought treatments.

Kalanchoe daigremontiana utilizes plantlet formation between its zigzag leaf margins as its method of asexual reproduction. In this study, K. daigremontiana SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (KdSOC1), a key intermediate in the transition from vegetative to asexual growth, was cloned. Furthermore, its expression profiles during plantlet formation under different environmental and hormone induction conditions were analyzed. The full-KdSOC1 cDNA sequence length was 1410 bp with 70% shared homology with Carya cathayensis SOC1. The conserved domain search of KdSOC1 showed the absence of I and C domains, which might indicate novel biological functions in K. daigremontiana. The full-KdSOC1 promoter sequence was 1401 bp long and contained multiple-hormone-responsive cis-acting elements. Hormone induction assays showed that gibberellins and salicylic acid mainly regulated KdSOC1 expression. The swift change from low to high KdSOC1 expression levels during long-day induction was accompanied by the rapid emergence of plantlets. Drought stress stimulated KdSOC1 expression in leaves both with and without plantlet formation. Together, the results suggested that KdSOC1 was closely involved in environmental stimulation signal perception and the transduction of K. daigremontiana plantlet formation. Therefore, future identification of KdSOC1 functions might reveal key information that will help elucidate the transition network between embryogenesis and organogenesis during plantlet formation.

Callogenesis in leaves of Kalanchoe pinnata Lam. by 2, 4-D and BA action / Calogênese em folhas de Kalanchoe pinnata Lam. pela ação de 2, 4-D e BAP

The Kalanchoe pinnata Lam. is a bush species of the Crassulaceae that is distinguished by its important medicinal properties. Its leaves are used as cataplasm to treat headaches and wounds. There is evidence for a hypotensive and anti-inflammatory effect. Techniques of plant tissue culture have been applied to plant species that produce substances likely to be explored in pharmacology, cell suspension being the main technique. At the industrial level, this method utilizes bioreactors in order to produce secondary metabolites on a large scale. The objective of this study was to evaluate the effects of in vitro combinations of 2,4-dichlorophenoxiacetic acid (2,4-D) and benzylaminopurine (BA) on callus induction in leaf explants of K. pinnata. Leaf fragments were inoculated in MS medium supplemented with 3.0% sucrose, 0.8% agar and factorial combinations of 2,4-D (0.00, 4.52, 9.06, 18.12 µM) and BA (0.00, 4.44, 8.88, 17.76 µM). The cultures were kept in the darkness at 24±2ºC for 50 days. The percentage of callus induction and the area of explants covered by callus cells were evaluated. In the absence of growth regulators, callus induction did not occur, with necrosis of all explants. The highest percentage of callus induction was 100%, obtained with the combination of 9.06 µM 2,4-D and 8.88 µM BA, but the calluses covered only 25% of the leaf area. The most efficient combination was 4.52 µM 2,4-D and 8.88 µM BA, resulting in 91% callus induction with 50 to 100% of the explants being covered by callus cells.

Kalanchoe pinnata Lam. é uma espécie arbustiva da família Crassulaceae que apresenta interessantes propriedades medicinais. Suas folhas são utilizadas em cataplasma para tratar enxaqueca e ferimentos. Há evidência de seu efeito como hipotensiva e anti-inflamatória. Técnicas de cultura de tecidos vegetais têm sido aplicadas para espécies que possuem substâncias passíveis de exploração na farmacologia, sendo a suspensão celular a principal técnica utilizada. A nível industrial, este método utiliza biorreatores para produzir metabólitos secundários em larga escala. Este estudo teve como objetivo avaliar os efeitos in vitro de combinações do ácido 2,4-diclorofenoxiacético (2,4-D) e de benzilaminopurina (BAP) na indução de calos em explantes foliares de K. pinnata. Fragmentos foliares foram inoculados em meio MS contendo 3% de sacarose, 0,8% de ágar e combinações fatoriais de 2,4-D (0,00; 4,52; 9,06 e 18,12 µM) e BAP (0,00; 4,44; 8,88 e 17,76 µM). Os cultivos foram mantidos no escuro, a 24±2ºC por 50 dias. A porcentagem de indução de calos e a área dos explantes coberta por células de calos foram avaliadas. Na ausência de reguladores de crescimento não ocorreu indução de calos, com necrose de todos os explantes. A porcentagem mais alta de indução de calos foi de 100%, obtida com a combinação de 9,06 µM de 2,4-D e 8,88 µM de BAP, mas estes calos cobriram apenas 25% da área foliar. A combinação mais eficiente foi de 9,06 µM de 2,4-D e 8,88 µM de BAP, que resultou em 91% de indução e 50 a 100% da área dos explantes coberta por células de calos.