Data from: Tomato GOLDEN2-LIKE transcription factors reveal molecular gradients that function during fruit development and ripening

Fruit ripening is the summation of changes rendering fleshy fruit tissues attractive and palatable to seed dispersing organisms. For example, sugar content is influenced by plastid numbers and photosynthetic activity in unripe fruit and later by starch and sugar catabolism during ripening. Tomato fruit are sinks of photosynthate, yet unripe green fruit contribute significantly to the sugars that ultimately accumulate in the ripe fruit. Plastid numbers and chlorophyll content are influenced by numerous environmental and genetic factors and are positively correlated with photosynthesis and photosynthate accumulation. GOLDEN2-LIKE (GLK) transcription factors regulate plastid and chlorophyll levels. Tomato (Solanum lycopersicum), like most plants, contains two GLKs (i.e., GLK1 and GLK2/UNIFORM). Mutant and transgene analysis demonstrated that these genes encode functionally similar peptides, though differential expression renders GLK1 more important in leaves, while GLK2 is predominant in fruit. A latitudinal gradient of GLK2 expression influences the typical uneven coloration of green and ripe wild-type fruit. Transcriptome profiling revealed a broader fruit gene expression gradient throughout development. The gradient influenced general ripening activities beyond plastid development and was consistent with the easily observed yet poorly studied ripening gradient present in tomato and many fleshy fruits.

果实成熟是一系列生理变化的整体过程，此类变化可使肉质果组织对种子传播生物兼具吸引力与适口性。例如，果实的糖分含量首先受未成熟阶段的质体（plastid）数量与光合活性调控，随后在成熟阶段受淀粉与糖类的分解代谢影响。番茄果实为光合产物库，但其未成熟的绿色果实在最终积累于成熟果实的糖分中占据了显著贡献份额。质体数量与叶绿素含量受诸多环境与遗传因素调控，且与光合速率及光合产物积累量呈正相关关系。GOLDEN2-LIKE（GLK）转录因子可调控质体与叶绿素的水平。与多数植物一样，番茄（Solanum lycopersicum）拥有两种GLK基因，即GLK1与GLK2/UNIFORM。突变体与转基因分析表明，这两种基因编码的肽类功能相似，但因表达模式存在差异，GLK1在叶片中的作用更为关键，而GLK2则在果实中占主导地位。GLK2表达的纬度梯度会影响野生型果实于绿色未成熟阶段及成熟阶段的典型不均匀着色现象。转录组分析（Transcriptome profiling）揭示了果实整个发育周期中更为广泛的基因表达梯度。该表达梯度不仅调控质体发育之外的一般成熟进程，还与番茄及众多肉质果中普遍存在、但尚未得到充分研究的成熟梯度现象相契合。