Nitrate and manganese (Mn) are necessary elements for the growth and development of rice in paddy soil. Under physiological conditions, we previously reported that the uptake of Mn in roots can be improved by the addition of external nitrate but not ammonium. To investigate the mechanism(s) of this phenotype, we produced plant lines overexpressing OsNRT2.1 and assessed Mn uptake under alternating wet and dry (AWD) and waterlogged (WL) conditions. Under AWD condition, we observed a 31% reduction in grain yields of wild type (WT) plants compared to WL condition. Interestingly, the overexpression of OsNRT2.1 could recover this loss, as OsNRT2.1 transgenic lines displayed higher grain yields than WT plants. We also observed 60% higher grain Mn in the transgenic lines in AWD condition and approximately 30% higher Mn in the grain of transgenic lines in WL condition. We further found that the overexpression of OsNRT2.1 did not alter Mg and Fe in the seeds in either growth condition. The reasons for the increased Mn content in OsNRT2.1 transgenic seeds in AWD condition could be explained by the elevated expression of OsNRAMP family genes including OsNRAMP3, OsNRAMP5, and OsNRAMP6 in node I, the panicle-neck, and the flag leaves. The mechanism(s) underpinning the upregulation of these genes requires further investigation. Taken together, our results provide a new function of OsNRT2.1 in improving rice yields and grain Mn accumulation during water-saving cultivation patterns. This represents a new strategy for maintaining yield and improving food quality in a sustainable agricultural system.

BACKGROUND The field population of Spodoptera exigua, an intermittently occurring polyphagous pest, has developed resistance to chlorantraniliprole, while whether or not such resistance carries fitness costs remains poorly understood. Here we selected six generations of the Leshan population (LS‐P) by two‐way selecting method, and obtained a highly resistant strain (CH‐RE) and resistant degeneration strain (CH‐SE) sharing a similar genetic background. After that fitness costs were evaluated by comparing the life history characteristics of CH‐RE, CH‐SE and the laboratory susceptible strain (SE‐Lab) via the age‐stage two‐sex life table method. RESULTS The resistance ratio of CH‐RE and CH‐SE were 226.69‐fold and 3.72‐fold, respectively, and the estimated realized heritability (h2) of CH‐RE was 0.058. Compared with CH‐SE, the duration of pre‐adult, the longevity of adult, adult preoviposition period (APOP) and average generation time (T) of CH‐RE had significantly increased, but the oviposition days, average fecundity, intrinsic growth rate (r), weekly growth rate (λ) and reproductive rate (R0) decreased significantly. Moreover, the relative fitness of CH‐RE was 0.25, and showed fitness costs. Concurrently, the fecundity of CH‐SE was slightly lower than SE‐Lab, but there was no significant difference in r, λ and R0, and the fitness (1) of CH‐SE was similar to SE‐Lab (1.02), which was no fitness cost. CONCLUSION These findings represent that chlorantraniliprole resistance in S. exigua has a fitness cost, and the fitness cost will disappear with the recovery of sensitivity when the insecticide is stopped for field populations, supporting that such resistance would be managed by switching off the selection pressure with rotation with alternate insecticides. © 2020 Society of Chemical Industry