Explore the vast range of titles available.

KNOX and BELL transcription factors regulate distinct steps of diploid development in plants. In the green alga Chlamydomonas reinhardtii, KNOX and BELL proteins are inherited by gametes of the opposite mating types and heterodimerize in zygotes to activate diploid development. By contrast, in land plants such as Physcomitrium patens and Arabidopsis thaliana , KNOX and BELL proteins function in sporophyte and spore formation, meristem maintenance and organogenesis during the later stages of diploid development. However, whether the contrasting functions of KNOX and BELL were acquired independently in algae and land plants is currently unknown. Here, we show that in the basal land plant species Marchantia polymorpha , gamete-expressed KNOX and BELL are required to initiate zygotic development by promoting nuclear fusion in a manner strikingly similar to that in C. reinhardtii . Our results indicate that zygote activation is the ancestral role of KNOX/BELL transcription factors, which shifted toward meristem maintenance as land plants evolved.

Key messagePlant-specific Dof transcription factors VDOF1 and VDOF2 are novel regulators of vascular cell differentiation through the course of a lifetime in Arabidopsis, with shifting their transcriptional target genes.Vascular system is one of critical tissues for vascular plants to transport low-molecular compounds, such as water, minerals, and the photosynthetic product, sucrose. Here, we report the involvement of two Dof transcription factors, named VASCULAR-RELATED DOF1 (VDOF1)/VDOF4.6 and VDOF2/VDOF1.8, in vascular cell differentiation and lignin biosynthesis in Arabidopsis. VDOF genes were expressed in vascular tissues, but the detailed expression sites were partly different between VDOF1 and VDOF2. Vein patterning and lignin analysis of VDOF overexpressors and double mutant vdof1 vdof2 suggested that VDOF1 and VDOF2 would function as negative regulators of vein formation in seedlings, and lignin deposition in inflorescence stems. Interestingly, effects of VDOF overexpression in lignin deposition were different by developmental stages of inflorescence stems, and total lignin contents were increased and decreased in VDOF1 and VDOF2 overexpressors, respectively. RNA-seq analysis of inducible VDOF overexpressors demonstrated that the genes for cell wall biosynthesis, including lignin biosynthetic genes, and the transcription factor genes related to stress response and brassinosteroid signaling were commonly affected by VDOF1 and VDOF2 overexpression. Taken together, we concluded that VDOF1 and VDOF2 are novel regulators of vascular cell differentiation through the course of a lifetime, with shifting their transcriptional target genes: in seedlings, the VDOF genes negatively regulate vein formation, while at reproductive stages, the VDOF proteins target lignin biosynthesis.

One crucial problem that plants faced during their evolution, particularly during the transition to growth on land, was how to transport water, nutrients, metabolites, and small signaling molecules within a large, multicellular body. As a solution to this problem, land plants developed specific tissues for conducting molecules, called water-conducting cells (WCCs) and food-conducting cells (FCCs). The well-developed WCCs and FCCs in extant plants are the tracheary elements and sieve elements, respectively, which are found in vascular plants. Recent molecular genetic studies revealed that transcriptional networks regulate the differentiation of tracheary and sieve elements, and that the networks governing WCC differentiation are largely conserved among land plant species. In this review, we discuss the molecular evolution of plant conducting cells. By focusing on the evolution of the key transcription factors that regulate vascular cell differentiation, the NAC transcription factor VASCULAR-RELATED NAC-DOMAIN for WCCs and the MYB-coiled-coil (CC)-type transcription factor ALTERED PHLOEM DEVELOPMENT for sieve elements, we describe how land plants evolved molecular systems to produce the specialized cells that function as WCCs and FCCs.

Arabidopsis (Arabidopsis thaliana) VASCULAR-RELATED NAC-DOMAIN1 (VND1) to VND7 encode a group of NAC domain transcription factors that function as master regulators of xylem vessel element differentiation. These transcription factors activate the transcription of genes required for secondary cell wall formation and programmed cell death, key events in xylem vessel element differentiation. Because constitutive overexpression of VND6 and VND7 induces ectopic xylem vessel element differentiation, functional studies of VND proteins have largely focused on these two proteins. Here, we report the roles of VND1, VND2, and VND3 in xylem vessel formation in cotyledons. Using our newly established in vitro system in which excised Arabidopsis cotyledons are stimulated to undergo xylem cell differentiation by cytokinin, auxin, and brassinosteroid treatment, we found that ectopic xylem vessel element differentiation required VND1, VND2, and VND3 but not VND6 or VND7. The importance of VND1, VND2, and VND3 also was indicated in vivo; in the vnd1 vnd2 vnd3 seedlings, xylem vessel element differentiation of secondary veins in cotyledons was inhibited under dark conditions. Furthermore, the light responsiveness of VND gene expression was disturbed in the vnd1 vnd2 vnd3 mutant, and vnd1 vnd2 vnd3 failed to recover lateral root development in response to the change of light conditions. These findings suggest that VND1 to VND3 have specific molecular functions, possibly linking light conditions to xylem vessel formation, during seedling development.

The development of cells specialized for water conduction or support is a striking innovation of plants that has enabled them to colonize land. The NAC transcription factors regulate the differentiation of these cells in vascular plants. However, the path by which plants with these cells have evolved from their nonvascular ancestors is unclear. We investigated genes of the moss Physcomitrella patens that encode NAC proteins. Loss-of-function mutants formed abnormal water-conducting and supporting cells, as well as malformed sporophyte cells, and overexpression induced ectopic differentiation of water-conducting–like cells. Our results show conservation of transcriptional regulation and cellular function between moss and Arabidopsis thaliana water-conducting cells. The conserved genetic basis suggests roles for NAC proteins in the adaptation of plants to land.

Gene homology helps us understand gene function and speciation. The number of plant genes and species registered in public databanks is continuously increasing. It is useful to associate homologous genes of various plants to better understand plant speciation. We designed the Gcorn plant database for the retrieval of information on homology and evolution of a plant gene of interest. Amino acid sequences of 73 species (62 land plants and 11 green algae), containing 2,682,261 sequences, were obtained from the National Center for Biotechnology Information (NCBI) Reference Sequence database. Based on NCBI BLAST searches between these sequences, homologous genes were grouped at various thresholds of homology indices devised by the authors. To show functional and evolutionary traits of a gene of interest, a phylogenetic tree, connecting genes with high homology indices, and line charts of the numbers of genes with various homology indices, are depicted. In addition, such indices are projected on a network graph in which species studied are connected based on the ratios of homologous genes, and on a phylogenetic tree for species based on NCBI Taxonomy. Gcorn plant provides information on homologous genes at various virtual time points along with speciation in plants.

Key messageThe homologs of VASCULAR RELATED NAC-DOMAIN in the peat moss Sphagnum palustre were identified and these transcriptional activity as the VNS family was conserved.In angiosperms, xylem vessel element differentiation is governed by the master regulators VASCULAR RELATED NAC-DOMAIN6 (VND6) and VND7, encoding plant-specific NAC transcription factors. Although vessel elements have not been found in bryophytes, differentiation of the water-conducting hydroid cells in the moss Physcomitrella patens is regulated by VND homologs termed VND-NST-SOMBRERO (VNS) genes. VNS genes are conserved in the land plant lineage, but their functions have not been elucidated outside of angiosperms and P. patens. The peat moss Sphagnum palustre, of class Sphagnopsida in the phylum Bryophyta, does not have hydroids and instead uses hyaline cells with thickened, helical-patterned cell walls and pores to store water in the leaves. Here, we performed whole-transcriptome analysis and de novo assembly using next generation sequencing in S. palustre, obtaining sequences for 68,305 genes. Among them, we identified seven VNS-like genes, SpVNS1-A, SpVNS1-B, SpVNS2-A, SpVNS2-B, SpVNS3-A, SpVNS3-B, and SpVNS4-A. Transient expression of these VNS-like genes, with the exception of SpVNS2-A, in Nicotiana benthamiana leaf cells resulted in ectopic thickening of secondary walls. This result suggests that the transcriptional activity observed in other VNS family members is functionally conserved in the VNS homologs of S. palustre.

The genus is stem parasitic angiosperms that parasitize a wide range of vascular plants via de novo formation of a distinctive parasitic organ called a haustorium. In the developing haustorium, meristematic cells, which are initiated from the stem cortical tissue, differentiate into haustorial parenchyma cells, which elongate, penetrate into the host tissues, and finally connect with the host vasculature. This interspecific vasculature connection allows the parasite to uptake water and nutrients from the host plant. Although histological aspects of haustorium development have been studied extensively, the molecular mechanisms underlying vasculature development and the interspecific connection with the host vasculature remain largely unknown. To gain insights into the interspecific cell-to-cell interactions involved in haustorium development, we established an haustorium induction system for using rosette leaves as the host plant tissue. The induction system was used to show that interaction with host tissue was required for the differentiation of parasite haustorial cells into xylem vessel cells. To further characterize the molecular events occurring during host-dependent xylem vessel cell differentiation in , we performed a transcriptome analysis using samples from the induction system. The results showed that orthologs of genes involved in development and proliferation of vascular stem cells were up-regulated even in the absence of host tissue, whereas orthologs of genes required for xylem vessel cell differentiation were up-regulated only after some haustorial cells had elongated and contacted the host xylem. Consistent results were obtained by another transcriptome analysis of the haustorium development in undergoing parasitization of an intact host plant. These findings suggest the involvement of host-derived signals in the regulation of non-autonomous xylem vessel differentiation and suggest that its connection to the host xylem during the haustorium development activates a set of key genes for differentiation into xylem vessel cells.

Developmental plasticity is one of the most striking features of plant morphogenesis, as plants are able to vary their shapes in response to environmental cues. Biotic or abiotic stimuli often promote organogenesis events in plants not observed under normal growth conditions. Root-knot nematodes (RKNs) are known to parasitize multiple species of rooting plants and to induce characteristic tissue expansion called galls or root-knots on the roots of their hosts by perturbing the plant cellular machinery. Galls contain giant cells (GCs) and neighboring cells, and the GCs are a source of nutrients for the parasitizing nematode. Highly active cell proliferation was observed in galls. However, the underlying mechanisms that regulate the symptoms triggered by the plant-nematode interaction have not yet been elucidated. In this study, we deciphered the molecular mechanism of gall formation with an infection assay system using RKN , and the model plant By taking advantages of this system, we performed next-generation sequencing-based transcriptome profiling, and found that the expression of procambium identity-associated genes were enriched during gall formation. Clustering analyses with artificial xylogenic systems, together with the results of expression analyses of the candidate genes, showed a significant correlation between the induction of gall cells and procambium-associated cells. Furthermore, the promoters of several procambial marker genes such as , and were activated not only in -induced galls, but similarly in induced-galls and -induced syncytia. Our findings suggest that phytoparasitic nematodes modulate the host's developmental regulation of the vascular stem cells during gall formation.