Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs that supply mineral nutrients to the host plant in exchange for carbon derived from photosynthesis. Sucrose is the end-product of photosynthesis and the main compound used by plants to translocate photosynthates to non-photosynthetic tissues. AMF alter carbon distribution in plants by modifying the expression and activity of key enzymes of sucrose biosynthesis, transport, and/or catabolism. Since sucrose is essential for the maintenance of all metabolic and physiological processes, the modifications addressed by AMF can significantly affect plant development and stress responses. AMF also modulate plant lipid biosynthesis to acquire storage reserves, generate biomass, and fulfill its life cycle. In this review we address the most relevant aspects of the influence of AMF on sucrose and lipid metabolism in plants, including its effects on sucrose biosynthesis both in photosynthetic and heterotrophic tissues, and the influence of sucrose on lipid biosynthesis in the context of the symbiosis. We present a hypothetical model of carbon partitioning between plants and AMF in which the coordinated action of sucrose biosynthesis, transport, and catabolism plays a role in the generation of hexose gradients to supply carbon to AMF, and to control the amount of carbon assigned to the fungus.

Los hongos micorrizógenos arbusculares (HMA) son biótrofos obligados de plantas y constituyen uno de los grupos de microorganismos del suelo de distribución más extensa. Una parte fundamental del estudio de estos organismos se ha enfocado a su clasificación, taxonomía y establecimiento de relaciones evolutivas entre HMA. El proceso en el desarrollo de este conocimiento puede ser separado en tres etapas importantes a partir de las primeras observaciones reportadas de estos microorganismos. La primera etapa corresponde al reconocimiento de la diversidad de especies dentro del género Endogone (Zygomycota) y su división en los géneros de HMA Gigaspora, Acaulospora, Glomus y Sclerocystis, así como en los géneros Modicella, Glaziella y Endogone, que no forman micorriza, todos ellos subordinados a Endogonaceae. La segunda etapa involucra el estudio de distintas características morfológicas comunes dentro del grupo de HMA que fueron suficientes para sustentar su separación en un grupo monofilético a nivel de orden (Glomales). Finalmente, la tercer etapa comprende los estudios más recientes en los que se incluye el uso de herramientas de biología molecular, aunado a las observaciones de las características morfológicas, en donde una de las aportaciones más significativas fue identificar y colocar al grupo de HMA en una posición taxonómica superior, agrupando las especies que integraban al orden Glomales en el phylum Glomeromycota. En la presente revisión se aborda cada una de estas etapas en forma detallada, además se presenta un panorama general de los distintos movimientos taxonómicos a los que los HMA han sido sujetos a lo largo de la historia de su estudio.

The exchange of phosphorus (P) and carbon (C) between plants and arbuscular mycorrhizal fungi (AMF) is a major determinant of their mutualistic symbiosis. We explored the C dynamics in tomato (Solanum lycorpersicum) inoculated or not with Rhizophagus irregularis to study their growth response under different NaH2PO4 concentrations (Null P, 0 mM; Low P, 0.065 mM; High P, 1.3 mM). The percentage of AMF colonization was similar in plants under Null and Low P, but severely reduced under High P. However, the AMF mass biomarker 16:1ω5 revealed higher fungal accumulation in inoculated roots under Low P, while more AMF spores were produced in the Null P. Under High P, AMF biomass and spores were strongly reduced. Plant growth response to mycorrhiza was negative under Null P, showing reduction in height, biovolume index, and source leaf (SL) area. Under Low P, inoculated plants showed a positive response (e.g., increased SL area), while inoculated plants under High P were similar to non‐inoculated plants. AMF promoted the accumulation of soluble sugars in the SL under all fertilization levels, whereas the soluble sugar level decreased in roots under Low P in inoculated plants. Transcriptional upregulation of SlLIN6 and SlSUS1, genes related to carbohydrate metabolism, was observed in inoculated roots under Null P and Low P, respectively. We conclude that P‐limiting conditions that increase AMF colonization stimulate plant growth due to an increase in the source and sink strength. Our results suggest that C partitioning and allocation to different catabolic pathways in the host are influenced by AMF performance.