Photosynthetic tissues are dynamic structures whose homeostasis depends on the coordination of two antagonistic processes: self-maintenance and supporting sink tissues. The balance of these processes determines plant development, which might be mediated by cytokinin. However, little is known about the link between sucrose transport signaling and cytokinin. Rice (Oryza sativa) DNA BINDING WITH ONE FINGER11 (OsDOF11) is a transcription factor that mediates sucrose transport by inducing the expression of sucrose transporter genes. Here, we found that OsDOF11 loss-of-function mutants showed a semi-dwarf phenotype with a smaller cell length due to increased cytokinin content in source tissues. RNA sequencing and reverse transcription quantitative PCR (RT-qPCR) analyses revealed that genes involved in cytokinin signaling and metabolism were affected in osdof11 mutants. Yeast one-hybrid (Y-1-H), dual-luciferase reporter, and chromatin immunoprecipitation (ChIP) experiments showed that OsDOF11 directly binds to the promoter regions of Oryza sativa CYTOKININ OXIDASE/DEHYDROGENASE4 (OsCKX4). Moreover, mutation of osckx4 in the osdof11 osckx4 double mutant rescued the semi-dwarf phenotype of the osdof11 mutant. Interestingly, exogenous application of kinetin promoted OsDOF11 expression earlier than OsCKX4, and overexpression of Oryza sativa VIN3-LIKE 2 (OsVIL2) caused an increase in active cytokinin levels and induced OsDOF11 transcript levels. Taken together, our results suggest a model in which both a sucrose transport regulator (OsDOF11) and cytokinin via OsCKX4 establish a feedback loop to maintain dynamic tissue homeostasis.

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Different grain positions on the rice panicle have asynchronous flowering phenomenon. The difference between superior and inferior grains not only affects the yield, but also restricts the quality of rice. In this study, the cytokinin-related transgenic lines VIN3-LIKE 2 (OsVIL2)-OX (increased endogenous cytokinin content), Oryza sativa A-type response regulator (OsRR1)-OX, and Early heading date 1 (Ehd1)-OX (B-type response regulator) are used to analyze nutrient accumulation and starch physicochemical properties of superior and inferior grains from the physiological level. The research conclusions are as follows: The overexpression transgenic plants of OsVIL2, OsRR1, and Ehd1 result in an increase of average starch granule size and solubility, but decrease in apparent amylose content of superior and inferior grains, which further reduce the surface order of superior and inferior grains, and increase the relative crystallinity of superior grains. Increased cytokinin content possibly accelerates the accumulation of carbohydrates in superior and inferior grains by promoting the expression of OsRR1. In addition, Ehd1 might be the main gene that affects the production of inferior grains, and Ehd1 is also involved in the regulation of the surface order structure and crystallinity of starch from superior and inferior grains by cytokinin.