Transcriptomic Responses of Fall Armyworms (Spodoptera frugiperda) Feeding on a Resistant Maize Inbred Line Xi502 with High Benzoxazinoid Content

The fall armyworm (Spodoptera frugiperda) is a devastating invasive insect herbivore. Its success on its preferred host plant, maize (Zea mays), is supported by numerous specialized detoxification mechanisms that suppress the defense responses of maize. In this study, we used a resistant Chinese maize cultivar, Xi502, which showed slower growth and lower yield-related phenotypes compare with maize inbred line B73. Comparative transcriptomic analyses demonstrated that B73-fed fall armyworm larvae have a significantly faster transcriptomic re-configuration toward maturation compared to their siblings fed with Xi502 leaves, whereas a number of putative aromatic breakdown -related DEGs were specifically induced when feeding on Xi502. Targeted metabolomic quantification demonstrated that Xi502 contains significantly higher levels of various benzoxazinoid compounds. Artificial feeding with the structural analog of a benzoxazinoid compound preferentially accumulated in Xi502 demonstrated a significant growth inhibition effect on FAW larvae. These results provide important genetic material and preliminary evidence for further dissection of the FAW-resistance mechanism in maize.

Interactions with Arsenic: Mechanisms of Toxicity and Cellular Resistance in Eukaryotic Microorganisms

Arsenic (As) is quite an abundant metalloid, with ancient origin and ubiquitous distribution, which represents a severe environmental risk and a global problem for public health. Microbial exposure to As compounds in the environment has happened since the beginning of time. Selective pressure has induced the evolution of various genetic systems conferring useful capacities in many microorganisms to detoxify and even use arsenic, as an energy source. This review summarizes the microbial impact of the As biogeochemical cycle. Moreover, the poorly known adverse effects of this element on eukaryotic microbes, as well as the As uptake and detoxification mechanisms developed by yeast and protists, are discussed. Finally, an outlook of As microbial remediation makes evident the knowledge gaps and the necessity of new approaches to mitigate this environmental challenge.

Inhibition of photoferrotrophy by nitric oxide in ferruginous environments

Anoxygenic phototrophic Fe(II)-oxidizers (photoferrotrophs) are thought to have thrived in Earth’s ancient ferruginous oceans and played a primary role in the precipitation of Archean and Paleoproterozoic (3.8-1.85 Ga) banded iron formations (BIF). The end of BIF deposition by photoferrotrophs has often been interpreted as being the result a deepening of water column oxygenation below the photic zone concomitant with the proliferation of cyanobacteria. We suggest here that a potentially overlooked aspect influencing BIF precipitation by photoferrotrophs is competition with another anaerobic Fe(II)-oxidizing metabolism. It is speculated that microorganisms capable of coupling Fe(II) oxidation to the reduction of nitrate were also present early in Earth history when BIF were being deposited, but the extent to which they could compete with photoferrotrophs when favourable geochemical conditions overlapped is unknown. Utilizing microbial incubations and numerical modelling, we show that nitrate-reducing Fe(II)-oxidizers metabolically outcompete photoferrotrophs for dissolved Fe(II). Moreover, the nitrate-reducing Fe(II)-oxidizers inhibit photoferrotrophy via the production of toxic nitric oxide (NO). Four different photoferrotrophs, representing both green sulfur and purple non-sulfur bacteria, are susceptible to this toxic effect despite having genomic capabilities for NO detoxification. Indeed, despite NO detoxification mechanisms being ubiquitous in some groups of phototrophs at the genomic level (e.g. Chlorobi and Cyanobacteria) it is likely they would still be influenced by NO stress. We suggest that the production of NO during nitrate-reducing Fe(II) oxidation in ferruginous environments represents an as yet unreported control on the activity of photoferrotrophs in the ancient oceans and thus the mechanisms driving precipitation of BIF.