GIGANTEA (GI) genes have a central role in plant development and influence several processes. Hybrid aspen T89 (Populus tremula x tremuloides) trees with low GI expression engineered through RNAi show severely compromised growth. To study the effect of reduced GI expression on leaf traits with special emphasis on leaf senescence, we grafted GI-RNAi scions onto wild-type rootstocks and successfully restored growth of the scions. The RNAi line had a distorted leaf shape and reduced photosynthesis, probably caused by modulation of phloem or stomatal function, increased starch accumulation, a higher carbon-to-nitrogen ratio, and reduced capacity to withstand moderate light stress. GI-RNAi also induced senescence under long day (LD) and moderate light conditions. Furthermore, the GI-RNAi lines were affected in their capacity to respond to “autumn environmental cues” inducing senescence, a type of leaf senescence that has physiological and biochemical characteristics that differ from those of senescence induced directly by stress under LD conditions. Overexpression of GI delayed senescence under simulated autumn conditions. The two different effects on leaf senescence under LD or simulated autumn conditions were not affected by the expression of FLOWERING LOCUS T. GI expression regulated leaf senescence locally—the phenotype followed the genotype of the branch, independent of its position on the tree—and trees with modified gene expression were affected in a similar way when grown in the field as under controlled conditions. Taken together, GI plays a central role in sensing environmental changes during autumn and determining the appropriate timing for leaf senescence in Populus.

中文翻译：

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GIGANTEA以两种不同的方式影响树木的叶子衰老

GIGANTEA (GI) 基因在植物发育中具有核心作用并影响多个过程。通过 RNAi 工程改造的低 GI 表达的混合白杨 T89（Populus tremula x tremuloides）树表现出严重受损的生长。为了研究降低 GI 表达对叶片性状的影响，特别强调叶片衰老，我们将 GI-RNAi 接穗嫁接到野生型砧木上，并成功地恢复了接穗的生长。RNAi 系具有扭曲的叶形和减少的光合作用，这可能是由于韧皮部或气孔功能的调节、淀粉积累增加、碳氮比升高以及抵抗中等光胁迫的能力降低所致。GI-RNAi 还在长日照 (LD) 和中等光照条件下诱导衰老。此外，GI-RNAi 系在响应“秋季环境线索”诱导衰老的能力方面受到影响，这是一种叶片衰老，其生理和生化特征不同于在 LD 条件下直接由压力诱导的衰老。模拟秋季条件下 GI 延迟衰老的过表达。在 LD 或模拟秋季条件下对叶片衰老的两种不同影响不受 FLOWERING LOCUS T. GI 表达的影响局部地调节叶片衰老——表型遵循分支的基因型，与其在树上的位置无关——和树当在田间生长时，与在受控条件下生长的基因表达相似。综合起来，