Following cell division, fruit growth is characterized by both expansion through increases in cell volume and biomass accumulation in cells. Fruit growth is limited by carbon starvation; however, the mechanism controlling fruit growth under restricted carbohydrate supply is poorly understood. In a previous study using red-fleshed kiwifruit, we showed that long-term carbon starvation had detrimental effects on carbohydrate, anthocyanin metabolism, and fruit growth. To elucidate the mechanisms underlying the reduction in fruit growth during kiwifruit development, we integrated phytohormone profiling with transcriptomic and developmental datasets for fruit under high or low carbohydrate supplies. Phytohormone profiling of the outer pericarp tissue of kiwifruit showed a 6-fold reduction in total cytokinin concentrations in carbon-starved fruit, whilst other hormones were less affected. Principal component analysis visualised that cytokinin composition was distinct between fruit at 16 weeks after mid bloom, based on their carbohydrate supply status. Cytokinin biosynthetic genes (IPT, CYP735A) were significantly downregulated under carbon starvation, in agreement with the metabolite data. Several genes that code for expansins, proteins involved in cell wall loosening, were also downregulated under carbon starvation. In contrast to other fleshy fruits, our results suggest that cytokinins not only promote cell division, but also drive fruit cell expansion and growth in kiwifruit.

中文翻译：

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植物激素和转录组学分析揭示了在碳供应受限的情况下内源性细胞分裂素对猕猴桃生长的影响。

细胞分裂后，果实生长的特征是通过细胞体积的增加和细胞中生物量的积累而扩张。水果的生长受到碳饥饿的限制；然而，人们对在碳水化合物供应受限的情况下控制果实生长的机制了解甚少。在先前使用红肉猕猴桃的研究中，我们表明长期缺碳会对碳水化合物，花色苷代谢和水果生长产生不利影响。为了阐明猕猴桃发育过程中水果生长减少的潜在机制，我们将植物激素谱与转录组学和发育数据集相结合，以研究高碳水化合物或低碳水化合物供应下的水果。猕猴桃外果皮组织的植物激素谱显示，碳缺乏水果中总细胞分裂素浓度降低了6倍，而其他激素受影响较小。主成分分析显示，在开花中期16周时，根据果实的碳水化合物供应状况，细胞分裂素的组成在果实之间是不同的。与代谢物数据一致，在碳饥饿下细胞分裂素的生物合成基因（IPT，CYP735A）显着下调。在碳饥饿状态下，一些编码扩展酶的基因，即参与细胞壁松弛的蛋白质，也被下调。与其他肉质水果相反，我们的结果表明细胞分裂素不仅促进细胞分裂，而且还驱动猕猴桃中的水果细胞膨胀和生长。与代谢物数据一致，在碳饥饿下细胞分裂素的生物合成基因（IPT，CYP735A）显着下调。在碳饥饿状态下，一些编码扩展酶的基因，即参与细胞壁松弛的蛋白质，也被下调。与其他肉质水果相反，我们的结果表明细胞分裂素不仅促进细胞分裂，而且还驱动猕猴桃中的水果细胞膨胀和生长。与代谢物数据一致，在碳饥饿下细胞分裂素的生物合成基因（IPT，CYP735A）显着下调。在碳饥饿状态下，一些编码扩展酶的基因，即参与细胞壁松弛的蛋白质，也被下调。与其他肉质水果相反，我们的结果表明细胞分裂素不仅促进细胞分裂，而且还驱动猕猴桃中的水果细胞膨胀和生长。