| Peanut (Arachis hypogaea L.) is an important oil crop in China and it easily shows iron deficiency-induced chlorosis in calcareous soils. This phenomenon can be effectively improved when peanut intercropped with maize (Zea mays L.). The peanut/maize intercropping system can improve iron nutrition of peanut, which has been identified at physiological level via both field and pot experiments, and the DMA has been proved playing an important role in improving peanut iron nutrition in intercropping system. Besides, the preliminary studies of iron absorption and transport genes have been reported. Even so, the mechanism involved in this process remains unclear. In this study, by investigation the biological functions of iron-related genes of peanut the molecular mechanism of iron absorption and translocation in intercropped peanut was elucidated. Moreover, the molecular and ecological mechanism of peanut/maize intercropping improving iron nutrition of peanut was unraveled.To indentify the biological functions of iron-related genes of peanut, the transgenic tobacco and rice plants of induced expression of peanut AhIRT1gene and the transgenic rice plants by induced expression of AhNRAMP1, AhFRO1and AhYSL3.1genes in calcareous soils were investigated. The results showed that the growth and nutrient status of transgenic plants were obviously better than that of non-transgenic plants, suggesting induced expression of peanut iron-related genes in plants conferred enhanced tolerance to iron deprivation. Meanwhile, AhOPT1gene was isolated by suppression subtractive hybridization from the roots of monocropped and intercropped peanut. The mRNA level of AhOPT1was obviously induced by iron deficiency in both roots and leaves. Moreover, yeast complementation assays implied that AhOPT1encoded a functional iron transporter.In the pot experiments, compared with monocropping system, the pH of rhizosphere in intercopping system had been reduced in most peanut growth period while the available iron increased remarkably. Meanwhile, the concentration of soil Olsen-P and total nitrogen significantly decreased in intercopping system, which reduced chelation of iron and thus improved the availability of iron in rhizosphere. And the results from the field experiments also indicated that the concentration of available iron and zinc of rhizosphere tended to increase in intercopping system during the whole growth stages. In conclusion, peanut/maize intercropping dynamically regulated the rhizosphere environment. The mRNA levels of peanut iron absorption-related genes in intercropping and monocorpping were analyzed. The results showed AhNRAMP1, AhFRO1and AhYSL1genes were highly expressed in intercropped peanut during anthesis, which may result in effectively uptake of Fe(Ⅱ) and Fe(Ⅲ). Only AhYSLl gene was still highly expressed in intercropped peanut for absorption of Fe(Ⅲ) during pod-setting stage. No gene was regulated by intercropping system in pod filling stage. Besides, AhIRT1gene was regulated by peanut iron status in the whole growth period. Therefore, we concluded that the uptake of iron in intercropping peanut was affected by both intercropping system and the iron status of peanut.In field experiment, the iron distribution of peanut shoots in monocropping and intercropping system was investigated and it demonstrated that the iron distribution in intercropped peanut was remarkably changed during different growth stages, which is consistent with the demand of iron in peanut. The expression levels of peanut iron transport genes AhYSL3.1, AhFRDLl and AhOPT1from both field and pot experiments indicated that intercropping regulated the expression of these genes in different parts of peanut during different growth stages, which modified the translocation of iron and thus meet the iron demands of peanut in various growth periods. |
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