Widespread ancient whole‐genome duplications in Malpighiales coincide with Eocene global climatic upheavalCai, Liming; Xi, Zhenxiang; Amorim, André M.; Sugumaran, M.; Rest, Joshua S.; Liu, Liang; Davis, Charles C.
doi: 10.1111/nph.15357pmid: 30030969
Whole‐genome duplications (WGDs) are widespread and prevalent in vascular plants and frequently coincide with major episodes of global and climatic upheaval, including the mass extinction at the Cretaceous–Tertiary boundary (c. 65 Ma) and during more recent periods of global aridification in the Miocene (c. 10–5 Ma). Here, we explore WGDs in the diverse flowering plant clade Malpighiales.
Using transcriptomes and complete genomes from 42 species, we applied a multipronged phylogenomic pipeline to identify, locate, and determine the age of WGDs in Malpighiales using three means of inference: distributions of synonymous substitutions per synonymous site (Ks) among paralogs, phylogenomic (gene tree) reconciliation, and a likelihood‐based gene‐count method.
We conservatively identify 22 ancient WGDs, widely distributed across Malpighiales subclades. Importantly, these events are clustered around the Eocene–Paleocene transition (c. 54 Ma), during which time the planet was warmer and wetter than any period in the Cenozoic.
These results establish that the Eocene Climatic Optimum likely represents a previously unrecognized period of prolific WGDs in plants, and lends further support to the hypothesis that polyploidization promotes adaptation and enhances plant survival during episodes of global change, especially for tropical organisms like Malpighiales, which have tight thermal tolerances.
TWI1 regulates cell‐to‐cell movement of OSH15 to control leaf cell fateCui, Xuean; Zhang, Zhiguo; Wang, Yanwei; Wu, Jinxia; Han, Xiao; Gu, Xiaofeng; Lu, Tiegang
doi: 10.1111/nph.15390pmid: 30151833
Cell pattern formation in plant leaves has attracted much attention from both plant biologists and breeders. However, in rice, the molecular mechanism remains unclear.
Here, we describe the isolation and functional characterization of TWISTED‐LEAF1 (TWI1), a critical gene involved in the development of the mestome sheath, vascular bundle sheath, interveinal mesophyll and sclerenchyma in rice leaves. Mutant twi1 plants have twisted leaves which might be caused by the compromised development and disordered patterning of bundle sheath, sclerenchyma and interveinal mesophyll cells.
Expression of TWI1 can functionally rescue these mutant phenotypes. TWI1 encodes a transcription factor binding protein that interacts with OSH15, a class I KNOTTED1‐like homeobox (KNOX) transcription factor.
The cell‐to‐cell trafficking of OSH15 is restricted through its interaction with TWI1. Knockout or knockdown of OSH15 in twi1 rescues the twisted leaf phenotype. These studies reveal a key factor controlling cell pattern formation in rice leaves.
Comparison of plant–soil feedback experimental approaches for testing soil biotic interactions among ecosystemsGundale, Michael J.; Wardle, David A.; Kardol, Paul; Nilsson, Marie‐Charlotte
doi: 10.1111/nph.15367pmid: 30067296
The study of interactions and feedbacks between plants and soils is a rapidly expanding research area, and a primary tool used in this field is to perform glasshouse experiments where soil biota are manipulated. Recently, there has been vigorous debate regarding the correctness of methods for carrying out these types of experiment, and specifically whether it is legitimate to mix soils from different sites or plots (mixed soil sampling, MSS) or not (independent soil sampling, ISS) to create either soil inoculum treatments or subjects.
We performed the first empirical comparison of MSS vs ISS approaches by comparing growth of two boreal tree species (Picea abies and Pinus sylvestris) in soils originating from 10 sites near the boreal forest limit in northern Sweden, and 10 sites in the subarctic region where boreal forests may potentially expand as a result of climate change.
We found no consistent differences in the conclusions that we reached whether we used MSS or ISS approaches.
We propose that researchers should not choose a soil handling method based on arguments that one method is inherently more correct than the other, but rather that method choice should be based on correct alignment with specific research questions and goals.
Mechanical contribution of secondary phloem to postural control in trees: the bark side of the forceClair, Bruno; Ghislain, Barbara; Prunier, Jonathan; Lehnebach, Romain; Beauchêne, Jacques; Alméras, Tancrède
doi: 10.1111/nph.15375pmid: 30076782
To grow straight, plants need a motor system that controls posture by generating forces to offset gravity. This motor function in trees was long thought to be only controlled by internal forces induced in wood. Here we provide evidence that bark is involved in the generation of mechanical stresses in several tree species.
Saplings of nine tropical species were grown tilted and staked in a shadehouse and the change in curvature of the stem was measured after releasing from the pole and after removing the bark. This first experiment evidenced the contribution of bark in the up‐righting movement of tree stems.
Combined mechanical measurements of released strains on adult trees and microstructural observations in both transverse and longitudinal/tangential plane enabled us to identify the mechanism responsible for the development of asymmetric mechanical stress in the bark of stems of these species.
This mechanism does not result from cell wall maturation like in wood, or from the direct action of turgor pressure like in unlignified organs, but is the consequence of the interaction between wood radial pressure and a smartly organized trellis structure in the inner bark.
A neglected alliance in battles against parasitic plants: arbuscular mycorrhizal and rhizobial symbioses alleviate damage to a legume host by root hemiparasitic Pedicularis speciesSui, Xiao‐Lin; Zhang, Ting; Tian, Yu‐Qing; Xue, Rui‐Juan; Li, Ai‐Rong
doi: 10.1111/nph.15379pmid: 30078224
Despite their ubiquitous distribution and significant ecological roles, soil microorganisms have long been neglected in investigations addressing parasitic plant–host interactions. Because nutrient deprivation is a primary cause of host damage by parasitic plants, we hypothesized that beneficial soil microorganisms conferring nutrient benefits to parasitized hosts may play important roles in alleviating damage.
We conducted a pot cultivation experiment to test the inoculation effect of an arbuscular mycorrhizal fungus (Glomus mosseae), a rhizobium (Rhizobium leguminosarum) and their interactive effects, on alleviation of damage to a legume host (Trifolium repens) by two root hemiparasitic plants with different nutrient requirements (N‐demanding Pedicularis rex and P‐demanding P. tricolor).
Strong interactive effects between inoculation regimes and hemiparasite identity were observed. The relative benefits of microbial inoculation were related to hemiparasite nutrient requirements. Dual inoculation with the rhizobium strongly enhanced promotional arbuscular mycorrhizal effects on hosts parasitized by P. rex, but reduced the arbuscular mycorrhizal promotion on hosts parasitized by P. tricolor.
Our results demonstrate substantial contribution of arbuscular mycorrhizal and rhizobial symbioses to alleviating damage to the legume host by root hemiparasites, and suggest that soil microorganisms are critical factors regulating host–parasite interactions and should be taken into account in future studies.