Arbuscular mycorrhizal symbiosis affects the grain proteome of Zea mays: a field study

Mycorrhiza represent a widespread mutualistic association between most land plants, including agriculturally relevant species1, and arbuscular mycorrhizal (AM) fungi, a monophyletic group of soil microorganims belonging to the Glomeromycota phylum2. When the symbiosis is established, the fungus grows within the cells of the roots forming arbuscules, which is the main site of nutrient exchange between the fungus and the plant. Moreover, the fungus develops an extensive extraradical mycelium that enhances the absorption ability of the plant root system3. The success of AM symbiosis is mostly due to the benefits that both partners gain from this relationship. The fungal partner takes up both water and mineral nutrients, mainly phosphorus and nitrogen, from the soil, through its mycelium, and transfers these compounds via the symbiotic interface to the plant root cells4,5. In turn, the plant supplies the fungus with about 10–20% of the plant’s photosynthates. This symbiosis directly influences plant responses and plant physiology, both in the target organ (roots) and in shoots, and as recently demonstrated in fruits6,7,8,9. As a consequence of this plant-fungal relationship, the AM symbiosis enhanced yield and improved fruit quality (taste and vitamin concentration) in strawberry fruits6,7,8,9; modulated sugar and carotenoid concentrations in tomato fruits10; increased the accumulation of carotenoids, chlorophylls and tocopherol in green and red leaf lettuces11; improved the yield and quality of saffron (Crocus sativus L.)12; increased growth, flavour and yield in Allium sativum L. cultivated in field conditions13; impacted the phenolic content and antioxidant properties of artichoke leaves14; and modulated essential oil production in Artemisia annua L.15 and in Ocimum basilicum L.16,17. A large body of evidence has shown that the protein profile of Pteris vittata and Medicago truncatula root18,19,20, and P. vittata, Populus alba and Zea mays leaf21,22,23, are affected by AM symbiosis. The above mentioned studies found that the plant traits that were positively affected by AM fungi included photosynthesis, carbon fixation and energy production in leaves, and glycolysis in roots. Notwithstanding these results, there is very little data regarding the impact of AM fungi on the plant seed proteome. Maize (Zea mays L.) is one of the most important crops worldwide. Its economic and nutritional value is mainly due to the high starch content that represent about 75% of mature seed weight24. Maize is strongly dependent on mycorrhizae25. For example, in maize, the AM symbiosis enhances spike dry weight, spike length, spike circumference, and the dry weight and dimensions of the grain26. To better understand the effect of AM fungi on maize, the present study was undertaken with the aim of assessing the effects of a consortium of AM fungi on the maize kernel proteome, cultivated in open-field conditions.