ABERRANT CARBOHYDRATE PARTITIONING 1 modulates sucrose allocation by regulating cell wall formation in rice

Sucrose (Suc) is transported from source leaves to sink tissues to sustain plant growth, development, and crop yield. However, the molecular mechanisms underlying carbohydrate partitioning still remain largely unclear. Here, we report a rice (Oryza sativa) mutant aberrant carbohydrate partitioning 1 (acp1), which hyperaccumulates carbohydrates in leaves and exhibits leaf chlorosis and premature senescence. ACP1 encodes a novel protein that contains two conserved domains of unknown function, DUF4220 and DUF594. Subcellular localization in rice and tobacco showed that ACP1 was localized in the endoplasmic reticulum. In situ expression analysis showed that ACP1 was mainly expressed in vascular bundles. Dye and sugar export experiments suggested that sugar trafficking through vascular tissues was impaired in the acp1 mutant. The acp1 mutant exhibits a significant cellulose deficiency in its leaves. Transmission electron microscopy experiments found that the abnormal cell wall ultrastructure in acp1. Furthermore, turgor pressure in source leaves of acp1 decreased compared with WT. Together, these results suggest that ACP1 plays a critical role in the partitioning of carbohydrates by regulating cell wall formation, which in turn affects the overall carbohydrate distribution and plant physiology.