My top 10 picks for botanical research this year. I’m not a botanist, and although I am fascinated by plant physiology, I’m not intellectually able to keep up with that research. So I only really follow plant evolution, palaeobotany, and plant-arthropod interactions; I have tried to make the list more varied though. Picks and rankings are subjective, based on a master list of 17 papers. [OA] indicates an open-access paper.
Land plants (Embryophyta) are highly-specialised streptophyte green algae. Of the other streptophyte groups, three are variably recovered as the sister group to the land plants, the results depending on the genes and methods used, and none ending up with truly rigorous support: the Charales, the Coleochaetales, and the Zygnematales (pond scum). The Charales (stoneworts) are the ones commonly depicted in textbooks and have always gained the most support. This paper may change our view on things: it uses a large dataset of 160 phylogenetically-significant genes, and gets perfect support values for a Zygnematales+Embryophyta clade. This has numerous implications, chief of which is that multicellularity is a convergent land plant innovation rather than a condition inherited from an ancestor (as would be the scenario if Charales are the sister).
This paper studies the molecular basis for UV light detection (280-320 nm) in plants, by looking at the reactions of UVR8, a photoreceptor known to react to UV light. Christie et al. went classical in this paper: they used crystallographic methods to elucidate UVR8′s structure, best summarised as a doughnut; then they used targeted mutations to find out how the protein works. When inert, it’s found as a dimer: two doughnuts connected by bridges. When UV light shines on the plant, these bridges break due to electrons getting excited. The single doughnut then binds to another protein, COP1, to complete the reaction.
I’ve written an overview of C4 photosynthesis, so refer to that post for necessary background. This paper analyses various traits in grasses of the Chloridoideae and Panicoideae, grasses in which C4 photosynthesis is dominant (in the phylogeny above, yellow indicates C3, all other colours are types of C4). It finds that the evolution of these traits, as well as ecological preferences, are determined not by the evolution of C4 photosynthesis, but by phylogeny. In other words, it’s the ancestry that counts. This in turn has implications about how we should treat C4 photosynthesis: there is a tendency to lump C4 plants together as one functional group, regardless of phylogeny. This finding says we are better off sticking to phylogenetic lumping, since there is clear niche conservatism: C4 photosynthesis doesn’t determine the ecology of these plants. Ancestry does, and C4 photosynthesis just tags along.
This paper presents a cool hypothesis for a contributing factor to the great angiosperm radiation of the Cretaceous: leaf vein density (Dv in the above diagram) as a key feature. This is an observation in the fossil record, that the density of the veins increases in two bursts, once in the initial angiosperm radiation (100 Ma) and another time at 65 Ma to reach today’s levels. The greater vein density leads to vastly improved gas exchange rates, which would have provided them with a distinct advantage as the CO2 levels decreased in the Cretaceous, allowing them to more easily outcompete the conifers and other land plants.
This genomic analysis of a moss, Physcomitrella patens, finds that it has 57 nuclear gene families by horizontal gene transfer from bacteria, fungi, or viruses. 18 of them are inherited ancestrally; 18 of them are recent acquisitions; and 15 of them are also found in more derived land plants, passed on from the last common ancestor with mosses. To put these numbers into perspective, the functions of the acquired genes are essential, involved in defence and stress tolerance, hormone biosynthesis, and even DNA repair. The picture painted by these facts is one of a harsh environment that early land plants had to colonise, in which UV radiation was rampant and the ground was inhospitable; these genes enabled the early mosses to survive by helping DNA stability in early mosses (later plants got yellow pollen, the yellow pigment serving as a UV shield), and numerous stress tolerance mechanisms and development helpers to keep them surviving in the harsh environment.
This is some pretty cool research from an ecological and from a plant-insect interaction perspective. The study finds that plant defence systems can be synchronised with insect feeding times; at least it is so in the case of the caterpillar of Trichoplusia ni and the Arabidopsis weed this experiment was done on. The synchronisation is achieved not by detecting the caterpillar, but by circadian rhythms – when raised on the same day/night cycle, the plant’s defence system will adjust to be active at the same time as the caterpillar is active. When circadian mechanisms are interrupted or the hormone jasmonate’s production is deficient, then the synchronisation gets thrown off and the plant experiences much higher herbivory levels and are thus at a physiological disadvantage. I’m interested in seeing how this plays out in nature with day-active vs. night-active insects.
This paper reports the draft nuclear genome of the basal glaucophyte alga Cyanophora paradoxa. The most significant result is evidence for the monophyly of the Plantae, as even the untypical plastid of the glaucophytes appears to be homologous with that of the rhodophytes and green algae (together, these three groups make up the Plantae). The data gathered from the genome says that 274 of the alga’s proteins were transferred from endosymbiotic cyanobacteria, and that 444 gene families were transferred by horizontal gene transfer from other bacteria. Many of these proteins and genes are involved in photosynthesis and associated processes, as well as plastid integration, meaning that we now have more light shone on how built-in photosynthesis in plants first evolved.
Mosses are expected to be one of the earliest plants to have evolved on land, but their early fossil record has been severely lacking because of their very low preservation potential. This paper describes the oldest mosses to date, which grew in the tropical forests of the German Carboniferous. Older ones are still to be expected, but their lack is merely an example of an expected inadequacy in the fossil record.
I admittedly include this so high up because of the coolness factor, but it does bring up deeper issues. But first, the cool stuff: the plant has sticky leaves that grow underground. Nematodes stick to them, and the plant digests them. In other words, this is a carnivorous plant, and it uses a completely novel way to capture its food. The deeper ecological and evolutionary issue to be brought up is about how such a unique strategy can evolve.The plant grows in a region with one of the poorest soils of the world, the Brazilian Cerrado. So it could be that the evolution of carnivory is instigated by soil nutrient deficiencies, and so they eat animals in order to get those critical nutrients.
This paper reviews the early record of angiosperm fossils from Europe to propose a temporal framework for their megadiversification in the Cretaceous in which they outcompeted the conifers and other land plants. The scenario Coiffard et al. synchs up with the view from the North American record, so it can be viewed as reliable. The scenario has three bursts of diversification into new habitats. From the abstract: “(i) Barremian (ca. 130–125 Ma) freshwater lake-related wetlands; (ii) Aptian–Albian (ca. 125–100 Ma) understory floodplains (excluding levees and back swamps); and (iii) Cenomanian–Campanian (ca. 100–84 Ma) natural levees, back swamps, and coastal swamps.”