| Summary: | The pentose phosphate pathway (PPP) plays an important role in plant growth and development, and plant responses to biotic and abiotic stresses. Yet, whether the PPP regulates plant defenses against herbivorous insects remains unclear. In this study, we cloned a rice cytosolic 6-phosphogluconate dehydrogenase gene, <i>Os6PGDH1</i>, which encodes the key enzyme catalyzing the third step in the reaction involving the oxidative phase of the PPP, and explored its role in rice defenses induced by brown planthopper (BPH) <i>Nilaparvata lugens</i>. Levels of <i>Os6PGDH1</i> transcripts were detected in all five examined tissues, with the highest in outer leaf sheaths and lowest in inner leaf sheaths. <i>Os6PGDH1</i> expression was strongly induced by mechanical wounding, infestation of gravid BPH females, and jasmonic acid (JA) treatment. Overexpressing <i>Os6PGDH1</i> (oe6PGDH) decreased the height of rice plants and the mass of the aboveground part of plants, but slightly increased the length of plant roots. In addition, the overexpression of <i>Os6PGDH1</i> enhanced levels of BPH-induced JA, jasmonoyl-isoleucine (JA-Ile), and H<sub>2</sub>O<sub>2</sub>, but decreased BPH-induced levels of ethylene. Bioassays revealed that gravid BPH females preferred to feed and lay eggs on wild-type (WT) plants over oe6PGDH plants; moreover, the hatching rate of BPH eggs raised on oe6PGDH plants and the fecundity of BPH females fed on these were significantly lower than the eggs and the females raised and fed on WT plants. Taken together, these results indicate that <i>Os6PGDH1</i> plays a pivotal role not only in rice growth but also in the resistance of rice to BPH by modulating JA, ethylene, and H<sub>2</sub>O<sub>2</sub> pathways.
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