While monocots lack the ability to produce a vascular cambium or woody growth, some monocot lineages evolved a novel lateral meristem, the monocot cambium, which supports secondary radial growth of stems. In contrast to the vascular cambium found in woody angiosperm and gymnosperm species, the monocot cambium produces secondary vascular bundles, which have an amphivasal organization of tracheids encircling a central strand of phloem. Currently there is no information concerning the molecular genetic basis of the development or evolution of the monocot cambium. Here we report high‐quality transcriptomes for monocot cambium and early derivative tissues in two monocot genera,
For more than 225 million y, all seed plants were woody trees, shrubs, or vines. Shortly after the origin of angiosperms ∼140 million y ago (MYA), the Nymphaeales (water lilies) became one of the first lineages to deviate from their ancestral, woody habit by losing the vascular cambium, the meristematic population of cells that produces secondary xylem (wood) and phloem. Many of the genes and gene families that regulate differentiation of secondary tissues also regulate the differentiation of primary xylem and phloem, which are produced by apical meristems and retained in nearly all seed plants. Here, we sequenced and assembled a draft genome of the water lily
- Award ID(s):
- 1812116
- NSF-PAR ID:
- 10142453
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 117
- Issue:
- 15
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- p. 8649-8656
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract Yucca andCordyline . Monocot cambium transcript profiles were compared to those of vascular cambia and secondary xylem tissues of two forest tree species,Populus trichocarpa andEucalyptus grandis . Monocot cambium transcript levels showed that there are extensive overlaps between the regulation of monocot cambia and vascular cambia. Candidate regulatory genes that vary between the monocot and vascular cambia were also identified, and included members of the KANADI and CLE families involved in polarity and cell‐cell signaling, respectively. We suggest that the monocot cambium may have evolved in part through reactivation of genetic mechanisms involved in vascular cambium regulation. -
Summary Vascular stem cell maintenance is regulated by a peptide signaling involving Tracheary Element Differentiation Inhibitory Factor (TDIF) and Receptor TDR/PXY (Phloem intercalated with Xylem) and co‐receptor BAK1 (BRI1‐associated receptor kinase1). The regulatory mechanism of this signaling pathway is largely unknown despite its importance in stem cell maintenance in the vascular meristem.
We report that activation of a NAC domain transcription factor XVP leads to precocious Xylem differentiation, disruption of Vascular Patterning, and reduced cell numbers in vascular bundles. We combined molecular and genetic studies to elucidate the biological functions of XVP.
XVP is expressed in the cambium, localized on the plasma membrane and forms a complex with TDIF co‐receptors PXY‐BAK1. Simultaneous mutation of
XVP and its close homologousNAC048 enhances TDIF signaling. In addition, genetics analysis indicated that XVP promotes xylem differentiation through a known master regulator VASCULAR‐RELATED NAC‐DOMAIN6 (VND6). Expression analyses indicate that XVP activates CLAVATA3/ESR (CLE)‐related protein 44 (CLE44 ), the coding gene of TDIF, whereas TDIF repressesXVP expression, suggesting a feedback mechanism.Therefore, XVP functions as a negative regulator of the TDIF‐PXY module and fine‐tunes TDIF signaling in vascular development. These results shed new light on the mechanism of vascular stem cell maintenance.
-
Summary Eukaryotic cells represent an intricate collaboration between multiple genomes, even down to the level of multi‐subunit complexes in mitochondria and plastids. One such complex in plants is the caseinolytic protease (Clp), which plays an essential role in plastid protein turnover. The proteolytic core of Clp comprises subunits from one plastid‐encoded gene ( clpP1 ) and multiple nuclear genes. The clpP1 gene is highly conserved across most green plants, but it is by far the fastest evolving plastid‐encoded gene in some angiosperms. To better understand these extreme and mysterious patterns of divergence, we investigated the history of clpP1 molecular evolution across green plants by extracting sequences from 988 published plastid genomes. We find that clpP1 has undergone remarkably frequent bouts of accelerated sequence evolution and architectural changes (e.g. a loss of introns and RNA ‐editing sites) within seed plants. Although clpP1 is often assumed to be a pseudogene in such cases, multiple lines of evidence suggest that this is rarely true. We applied comparative native gel electrophoresis of chloroplast protein complexes followed by protein mass spectrometry in two species within the angiosperm genus Silene , which has highly elevated and heterogeneous rates of clpP1 evolution. We confirmed that clpP1 is expressed as a stable protein and forms oligomeric complexes with the nuclear‐encoded Clp subunits, even in one of the most divergent Silene species. Additionally, there is a tight correlation between amino acid substitution rates in clpP1 and the nuclear‐encoded Clp subunits across a broad sampling of angiosperms, suggesting continuing selection on interactions within this complex. -
Abstract Host races represent an important step in the speciation process of phytophagous insects as they reflect the maintenance of genetically divergent host‐associated populations in the face of appreciable gene flow. The red‐shouldered soapberry bug,
Jadera haematoloma (Herrich‐Schäffer) (Hemiptera: Rhopalidae), is an oligophagous seed predator with a history of host race evolution on plant associations in the (soapberry) family Sapindaceae. Soapberry bugs are a model group for understanding rapid ecological adaptation to their hosts, and hence good candidates for investigating evolutionary divergence in host associations over short timescales. Here, we describe the recent discovery of Mexican buckeye,Ungnadia speciosa Endl., as a host ofJ. haematoloma in a region of the Chihuahuan desert including west Texas and southeastern New Mexico, USA. This host differs fromJ. haematoloma ’s previously recorded hosts in the Sapindaceae in seed chemistry, ecology, and phylogeny. The tendency toward rapid, host‐associated adaptations by populations ofJ. haematoloma and the unique biology of the newly discoveredUngnadia host create the opportunity for potential host race formation, as it overlaps geographically with two previously recorded host plants in this region – the native western soapberry tree,Sapindus saponaria var.drummondii (Hook & Arn.), and the non‐native goldenrain tree,Koelreuteria paniculata Laxm. We explore the possibility of host race formation onUngnadia ‐associated insects by testing for host‐associated differentiation in morphology and feeding behaviors. We find evidence of differentiation in the length of the mouth parts, which is an ecologically relevant feeding trait between host plant species with larger or smaller seed capsules. This divergence is maintained in the face of potential gene flow by reproductive isolation in the form of habitat isolation, which we detect in host preference trials. Together, our results demonstrate that soapberry bugs associated with this newly discovered host exhibit morphological and behavioral traits consistent with host race formation, but additional work is required to confirm its state along the speciation continuum. -
Summary Disruption of photosynthesis and carbon transport due to damage to the tree crown and stem cambial cells, respectively, can cause tree mortality. It has recently been proposed that fire‐induced dysfunction of xylem plays an important role in tree mortality. Here, we simultaneously tested the impact of a lethal fire dose on nonstructural carbohydrates (NSCs) and xylem hydraulics in
Pinus ponderosa saplings.Saplings were burned with a known lethal fire dose. Nonstructural carbohydrates were assessed in needles, main stems, roots and whole plants, and xylem hydraulic conductivity was measured in the main stems up to 29 d postfire.
Photosynthesis and whole plant NSCs declined postfire. Additionally, all burned saplings showed 100% phloem/cambium necrosis, and roots of burned saplings had reduced NSCs compared to unburned and defoliated saplings. We further show that, contrary to patterns observed with NSCs, water transport was unchanged by fire and there was no evidence of xylem deformation in saplings that experienced a lethal dose of heat from fire.
We conclude that phloem and cambium mortality, and not hydraulic failure, were probably the causes of death in these saplings. These findings advance our understanding of the physiological response to fire‐induced injuries in conifer trees.