How do nitrogen and phosphorus deficiencies affect strigolactone production and exudation?

Plants exude strigolactones (SLs) to attract symbiotic arbuscular mycorrhizal fungi in the rhizosphere. Previous studies have demonstrated that phosphorus (P) deficiency, but not nitrogen (N) deficiency, significantly promotes SL exudation in red clover, while in sorghum not only P deficiency but also N deficiency enhances SL exudation. There are differences between plant species in SL exudation under P- and N-deficient conditions, which may possibly be related to differences between legumes and non-legumes. To investigate this possibility in detail, the effects of N and P deficiencies on SL exudation were examined in Fabaceae (alfalfa and Chinese milk vetch), Asteraceae (marigold and lettuce), Solanaceae (tomato), and Poaceae (wheat) plants. In alfalfa as expected, and unexpectedly in tomato, only P deficiency promoted SL exudation. In contrast, in Chinese milk vetch, a leguminous plant, and in the other non-leguminous plants examined, N deficiency as well as P deficiency enhanced SL exudation. Distinct reductions in shoot P levels were observed in plants grown under N deficiency, except for tomato, in which shoot P level was increased by N starvation, suggesting that the P status of the shoot regulates SL exudation. There seems to be a correlation between shoot P levels and SL exudation across the species/families investigated

Altered pattern of Arbuscular Mycorrhizal formation in tomato ethylene mutants

Although no specific role has been demonstrated for ethylene during Arbuscular Mycorrhizal (AM) symbiosis, recent results suggest its participation in the regulation of the AM. Analysis of arbuscular mycorrhizal colonization in the abscisic acid (ABA)-deficient tomato sitiens mutant has shown that ABA deficiency induced ethylene production. It has also been suggested that one of the mechanisms used by ABA to determine susceptibility to fungal infection is negative modulation of the ethylene pathway. In this study, we describe the pattern of mycorrhization in mutant plants with altered ethylene biosynthesis and/or perception pathways. Epinastic (epi) plants with increased ethylene response were unaffected in terms of mycorrhizal frequency, although this mutation had a considerable negative impact on the intensity of mycorrhizal root colonization. The negative impact of the mutation in epi plants on the intensity of mycorrhizal root colonization was associated with a transitory increase in the transcript level of the LeETR6 ethylene receptor gene. On the other hand, ripenenig-inhibitor (rin) tomato mutant plants were positively affected in relation to all the mycorrhizal colonization parameters measured, suggesting that, at least in tomato plants, the regulation of AM formation is mediated by the RIN pathway

The role of strigolactones in plant-microbe interactions

Plants associate with an infinite number of microorganisms that interact with their hosts in a mutualistic or parasitic manner. Evidence is accumulating that strigolactones (SLs) play a role in shaping these associations. The best described function of SLs in plant–microbe interactions is in the rhizosphere, where, after being exuded from the root, they activate hyphal branching and enhanced growth and energy metabolism of symbiotic arbuscular mycorrhiza fungi (AMF). Furthermore, an impact of SLs on the quantitative development of root nodule symbiosis with symbiotic nitrogen-fixing bacteria and on the success of fungal and bacterial leaf pathogens is beginning to be revealed. Thus far, the role of SLs has predominantly been studied in binary plant–microbe interactions. It can be predicted that their impact on the bacterial, fungal, and oomycetal communities (microbiomes), which thrive on roots, in the rhizosphere, and on aerial tissues, will be addressed in the near future

Strigolactones as mediators of plant growth responses to environmental conditions

Strigolactones (SLs) have been recently identified as a new group of plant hormones or their derivatives thereof, shown to play a role in plant development. Evolutionary forces have driven the development of mechanisms in plants that allow adaptive adjustments to a variety of different habitats by employing plasticity in shoot and root growth and development. The ability of SLs to regulate both shoot and root development suggests a role in the plant's response to its growth environment. To play this role, SL pathways need to be responsive to plant growth conditions, and affect plant growth toward increased adaptive adjustment. Here, the effects of SLs on shoot and root development are presented, and possible feedback loops between SLs and two environmental cues, light and nutrient status, are discussed; these might suggest a role for SLs in plants' adaptive adjustment to growth conditions