Multivariate genome-wide association study of leaf shape in a Populus deltoides and P. simonii F1 pedigree

Leaf morphology exhibits tremendous diversity between and within species, and is likely related to adaptation to environmental factors. Most poplar species are of great economic and ecological values and their leaf morphology can be a good predictor for wood productivity and environment adaptation. It is important to understand the genetic mechanism behind variation in leaf shape. Although some initial efforts have been made to identify quantitative trait loci (QTLs) for poplar leaf traits, more effort needs to be expended to unravel the polygenic architecture of the complex traits of leaf shape. Here, we performed a genome-wide association analysis (GWAS) of poplar leaf shape traits in a randomized complete block design with clones from F1 hybrids of Populus deltoides and Populus simonii. A total of 35 SNPs were identified as significantly associated with the multiple traits of a moderate number of regular polar radii between the leaf centroid and its edge points, which could represent the leaf shape, based on a multivariate linear mixed model. In contrast, the univariate linear mixed model was applied as single leaf traits for GWAS, leading to genomic inflation; thus, no significant SNPs were detected for leaf length, measures of leaf width, leaf area, or the ratio of leaf length to leaf width under genomic control. Investigation of the candidate genes showed that most flanking regions of the significant leaf shape-associated SNPs harbored genes that were related to leaf growth and development and to the regulation of leaf morphology. The combined use of the traditional experimental design and the multivariate linear mixed model could greatly improve the power in GWAS because the multiple trait data from a large number of individuals with replicates of clones were incorporated into the statistical model. The results of this study will enhance the understanding of the genetic mechanism of leaf shape variation in Populus. In addition, a moderate number of regular leaf polar radii can largely represent the leaf shape and can be used for GWAS of such a complicated trait in Populus, instead of the higher-dimensional regular radius data that were previously considered to well represent leaf shape.

The Fungal Effector Mlp37347 Alters Plasmodesmata Fluxes and Enhances Susceptibility to Pathogen

Melampsora larici-populina (Mlp) is a devastating pathogen of poplar trees, causing the defoliating poplar leaf rust disease. Genomic studies have revealed that Mlp possesses a repertoire of 1184 small secreted proteins (SSPs), some of them being characterized as candidate effectors. However, how they promote virulence is still unclear. This study investigates the candidate effector Mlp37347’s role during infection. We developed a stable Arabidopsis transgenic line expressing Mlp37347 tagged with the green fluorescent protein (GFP). We found that the effector accumulated exclusively at plasmodesmata (PD). Moreover, the presence of the effector at plasmodesmata favors enhanced plasmodesmatal flux and reduced callose deposition. Transcriptome profiling and a gene ontology (GO) analysis of transgenic Arabidopsis plants expressing the effector revealed that the genes involved in glucan catabolic processes are up-regulated. This effector has previously been shown to interact with glutamate decarboxylase 1 (GAD1), and in silico docking analysis supported the strong binding between Mlp37347 and GAD1 in this study. In infection assays, the effector promoted Hyalonoperospora arabidopsidis growth but not bacterial growth. Our investigation suggests that the effector Mlp37347 targets PD in host cells and promotes parasitic growth.

First report of the poplar leaf miner, Phyllonorycter populifoliella (Treitschke) (Lepidoptera: Gracillariidae) from India

Here we report about the discovery of the poplar leaf miner, Phyllonorycter populifoliella (Treitschke) in India. The mines of this micromoth were found in noticeable density on the leaves of poplar, Populus sp. (Salicaceae) in the northern mountainous region Ladakh in 2017–2018. We provide short morphological diagnosis, describe bionomics and analyze molecular data of Ph. populifoliella from India comparing sequences with those from other countries in Eurasia where the species is known as native. We also illustrate male and female genitalia, an adult of the moth, the leaf mines and the infestation plot in Ladakh, and discuss the occurrence of the species in the country.

Vermiculture as a biotechnological method of recultivation of disturbed lands in the post-mining system

The article shows the prospects of using the technology of vermicomposting for the biological re-cultivation of disturbed mining areas. The valuable properties of vermicompost as a component of soil-substituting mixtures for use in the re-cultivation of disturbed areas are considered. The expediency of using plant waste for the preparation of soil-substituting substrates is shown. The presence of special agrochemical properties of vermicompost obtained during the processing of plant waste (leaf litter) by the Eisenia fetida Savigny culture is experimentally established. The pH values and the content of calcium ions in the vermicompost based on poplar leaf litter were significantly higher than in the vermicompost based on horse manure – 7.61 vs. 6.98 and 112.3 vs. 83 mg-eq. / kg, respectively. Germination of wheat seeds on extracts from vermicompost obtained from poplar litter led to a statistically significant increase in the mass of the formed roots compared to seeds germinated on tap water.

Jasmonic Acid- and Ethylene-Induced Mitochondrial Alternative Oxidase Stimulates Marssonina brunnea Defense in Poplar

Mitochondrial processes are implicated in plant response to biotic stress caused by viruses, actinomyces, bacteria and pests, but their function in defense against fungal invasion remains unclear. Here, we investigated the role and regulation of mitochondrial alternative oxidase (AOX) in response to black spot disease caused by the hemibiotrophic fungus Marssonina brunnea in poplar. M. brunnea inoculation induced the transcription of the AOX1a gene in the mitochondrial electron transport chain and of jasmonic acid (JA) and ethylene (ET) biosynthetic genes, with the accumulation of these phytohormones in poplar leaf, while inhibiting the transcript amount of the mitochondrial cytochrome c oxidase gene (COX6b) and genes related to salicylic acid (SA). Enhanced AOX reduced poplar susceptibility to M. brunnea with a higher ATP/ADP ratio while the repressed AOX caused the reverse effect. Exogenous JA and 1-aminocyclopropane-1-carboxylic acid (ACC, a biosynthetic precursor of ET) inhibited the transcript amount of COX6b and consequently increased the ratio of AOX pathway to total respiration. Furthermore, the transcription of CYS C1 and CYS D1 genes catalyzing cyanide metabolism was induced, while the cysteine (CYS) substrate levels reduced upon M. brunnea inoculation; exogenous JA and ACC mimicked the effect of M. brunnea infection on cysteine. Exogenous SA enhanced, while JA and ACC reduced, poplar susceptibility to M. brunnea. Moreover, inhibiting AOX completely prohibited JA- and ET-increased tolerance to M. brunnea in poplar. These observations indicate that the JA- and ET-induced mitochondrial AOX pathway triggers defense against M. brunnea in poplar. This effect probably involves cyanide. These findings deepen our understanding of plant–pathogenic fungi interactions.