There is still no consensus on the true origin of fatal yellowing, one of the most important diseases affecting oil palm (Elaeis guineensis Jacq.) plantations. This study involved two-dimensional liquid chromatography coupled with tandem mass spectrometry (2D-UPLC-MSE) analyses to identify changes in protein profiles of oil palms affected by FY disease. Oil palm roots were sampled from two growing areas. Differential accumulation of proteins was assessed by comparing plants with and without symptoms and between plants at different stages of FY development. Most of the proteins identified with differential accumulation were those related to stress response and energy metabolism. The latter proteins include the enzymes alcohol dehydrogenase and aldehyde dehydrogenase, related to alcohol fermentation, which were identified in plants with and without symptoms. The presence of these enzymes suggests an anaerobic condition before or during FY. Transketolase, isoflavone reductase, cinnamyl alcohol dehydrogenase, caffeic acid 3-O-methyltransferase, S-adenosylmethionine synthase, aldehyde dehydrogenase and ferritin, among others, were identified as potential marker proteins and could be used to guide selection of FY-tolerant oil palm genotypes or to understand the source of this anomaly. When comparing different stages of FY, we observed high accumulation of alcohol dehydrogenase and other abiotic stress related-proteins at all disease stages. On the other hand, biological stress-related proteins were more accumulated at later stages of the disease. These results suggest that changes in abiotic factors can trigger FY development, creating conditions for the establishment of opportunistic pathogens.

The adaptation and performance of orchid mycorrhizae in heavy metal-polluted soils have been poorly explored. In the present study, proteomic and metabolic approaches were used to detect physiological changes in orchid roots established in a heavy metal-polluted soil and to ascertain whether mycorrhizal fungi affect the metabolic responses of roots. Young Bipinnula fimbriata plantlets were established in control and heavy metal-polluted soils in a greenhouse. After 14 months, exudation of root organic acids, phenolics, percentage of mycorrhization, mineral content, and differential protein accumulation were measured. More root biomass, higher root colonization, and higher exudation rates of citrate, succinate, and malate were detected in roots growing in heavy metal-polluted soils. Higher accumulation of phosphorus and heavy metals was found inside mycorrhizal roots under metal stress. Under non-contaminated conditions, non-mycorrhizal root segments showed enhanced accumulation of proteins related to carbon metabolism and stress, whereas mycorrhizal root segments stimulated protein synthesis related to pathogen control, cytoskeleton modification, and sucrose metabolism. Under heavy metal stress, the proteome profile of non-mycorrhizal root segments indicates a lower induction of defense mechanisms, which, together with the stimulation of enzymes related to carotenoid biosynthesis and cell wall organization, may positively influence mycorrhizal fungi colonization. The results point to different metabolic strategies in mycorrhizal and non-mycorrhizal root segments that are exposed to heavy metal stress. The results indicate that root colonization by mycorrhizal fungi is stimulated to alleviate the negative effects of heavy metals in the orchids.

Mimosa acutistipula var. ferrea (Fabaceae) is endemic to ferruginous tropical rocky outcrops in the eastern Amazon, also known as canga. Canga are often associated with mining activities and are the target of protection and rehabilitation projects. M. acutistipula stands out in this biodiversity hotspot with high growth rates, even in rehabilitating minelands (RMs). However, little is known about the diversity of soil microorganisms interacting with M. acutistipula in canga and RMs. This study analyzed the rhizosphere-associated bacterial and fungal microbial communities associated with M. acutistipula growing in an RM and a native shrub canga. The fungal phylum Ascomycota was the dominant taxa identified in the rhizosphere of the canga (RA: 98.1) and RM (RA: 93.1). The bacterial phyla Proteobacteria (RA: 54.3) and Acidobacteria (RA: 56.2) were the dominant taxa identified in the rhizosphere in the canga and RM, respectively. Beneficial genera such as Bradyrhizobium, Rhodoplanes, and Paraconiothyrium were identified in the rhizosphere of M. acutistipula in both areas. However, the analyses showed that the fungal and bacterial diversity differed between the rhizosphere of the canga and RM, and that the microbial taxa adapted to the canga (i.e., Rasamsonia, Scytalidium, Roseiarcus, and Rhodomicrobium) were lacking in the RM. This influences the microbe-mediated soil processes, affecting long-term rehabilitation success. The results showed that M. acutistipula established non-specific interactions with soil microorganisms, including beneficial taxa such as nitrogen-fixing bacteria, mycorrhizal fungi, and other beneficial endophytes, well known for their importance in plant adaptation and survival. High levels of microbe association and a plant’s ability to recruit a wide range of soil microorganisms help to explain M. acutistipula’s success in rehabilitating minelands.