Plant somatic cells have the remarkable ability to regenerate an entire organism. Many species in the genus Kalanchoë , known as ''mother of thousands,'' develop plantlets on the leaf margins. Using key regulators of organogenesis (STM) and embryogenesis (LEC1 and FUS3) processes, we analyzed asexual reproduction in Kalanchoë leaves. Suppression of STM abolished the ability to make plantlets. Here, we report that constitutive plantlet-forming species, like Kalanchoë daigremontiana, form plantlets by coopting both organogenesis and embryogenesis programs into leaves. These species have a defective LEC1 gene and produce nonviable seed, whereas species that produce plantlets only upon stress induction have an intact LEC1 gene and produce viable seed. The latter species are basal in the genus, suggesting that inducedplantlet formation and seed viability are ancestral traits. We provide evidence that asexual reproduction likely initiated as a process of organogenesis and then recruited an embryogenesis program into the leaves in response to loss of sexual reproduction within this genus.nlike animal cells, somatic cells of plants are capable of regenerating the entire adult organism, and this potential for regeneration is called totipotency. In some plants, this ability is used as a mechanism of vegetative reproduction (1) and may represent the only means of reproduction. Species in the genus Kalanchoë (Crassulaceae) reproduce asexually by forming plantlets along their leaf margins. Although some of these species produce plantlets only when placed under stress (induced plantlet-forming species), others spontaneously make plantlets on leaves (constitutive plantlet-forming species). To date, leaf plantlet development in Kalanchoë has been studied extensively at the morphological and anatomical levels (2-10). Although these studies have provided detailed descriptive information, the morphogenic process involved in the origin of these plantlets and the different reproductive strategies undertaken by species of this genus are still not well understood.Genetic analyses of model species have identified key molecular regulators of organogenesis and embryogenesis. Loss-offunction mutations in Arabidopsis SHOOT MERISTEMLESS (STM), a class 1 KNOTTED1-LIKE HOMEOBOX (KNOX1) gene, result in plants that are unable to form a shoot apical meristem (SAM) and arrest at the seedling stage (11, 12). Transgenic plants constitutively overexpressing KNOX1 genes form ectopic shoots on leaves (13-15). The Arabidopsis LEAFY COTYLEDON1 (LEC1) gene is expressed during embryogenesis, and its expression pattern is similar in both zygotic and somatic embryos (16)(17)(18). Loss-of-function mutation of LEC1 results in embryos that do not undergo developmental arrest and are nonviable because they are desiccation-intolerant (19)(20)(21)(22)(23). Ectopic expression of LEC1 in transgenic plants induces somatic embryos in vegetative cells (16). Because leaf-plantlet formation resembles aspects of both STM and LEC1 overexpression phenotypes, we investigate...

Infection of crop species by parasitic plants is a major agricultural hindrance resulting in substantial crop losses worldwide. Parasitic plants establish vascular connections with the host plant via structures termed haustoria, which allow acquisition of water and nutrients, often to the detriment of the infected host. Despite the agricultural impact of parasitic plants, the molecular and developmental processes by which host/parasitic interactions are established are not well understood. Here, we examine the development and subsequent establishment of haustorial connections by the parasite dodder (Cuscuta pentagona) on tobacco (Nicotiana tabacum) plants. Formation of haustoria in dodder is accompanied by upregulation of dodder KNOTTED-like homeobox transcription factors, including SHOOT MERISTEMLESS-like (STM). We demonstrate interspecific silencing of a STM gene in dodder driven by a vascular-specific promoter in transgenic host plants and find that this silencing disrupts dodder growth. The reduced efficacy of dodder infection on STM RNA interference transgenics results from defects in haustorial connection, development, and establishment. Identification of transgene-specific small RNAs in the parasite, coupled with reduced parasite fecundity and increased growth of the infected host, demonstrates the efficacy of interspecific small RNA-mediated silencing of parasite genes. This technology has the potential to be an effective method of biological control of plant parasite infection.

ORCID IDs: 0000-0002-3703-7531 (H.M.P.G.); 0000-0002-9930-1377 (V.M.R.S.); 0000-0002-8470-793X (M.K.).All members of Asteraceae, the largest flowering family, have a unique compressed inflorescence known as a capitulum, which resembles a solitary flower. The capitulum often consists of bilateral (zygomorphic) ray florets and radial (actinomorphic) disc florets. In Antirrhinum majus, floral zygomorphy is established by the interplay between dorsal petal identity genes, CYCLOIDEA (CYC) and RADIALIS (RAD), and a ventral gene DIVARICATA (DIV). To investigate the role of CYC, RAD, and DIV in the development of ray and disc florets within a capitulum, we isolated homologs of these genes from an Asteraceae species, Senecio vulgaris (common groundsel). After initial uniform expression of RAY3 (CYC), SvRAD, and SvDIV1B in ray florets only, RAY3 and SvRAD were exclusively expressed in the ventral petals of the ray florets. Our functional analysis further showed that RAY3 promotes and SvDIV1B represses petal growth, confirming their roles in floral zygomorphy. Our results highlight that while floral symmetry genes such as RAY3 and SvDIV1B appear to have a conserved role in petal growth in both Senecio and Antirrhinum, the regulatory relationships and expression domains are divergent, allowing ventral petal elongation in Senecio versus dorsal petal elongation in Antirrhinum. In S. vulgaris, diversification of CYC genes has led to novel interactions; SvDIV1B inhibits RAY3 and SvRAD, and may activate RAY2. This highlights how recruitment of floral symmetry regulators into dynamic networks was crucial for creating a complex and elaborate structure such as the capitulum.