Laboratory of Plant Developmental Genetics, Departamento de Ciências Biológicas, Escola Superior de Agricultura 'Luiz de Queiroz', Universidade de São Paulo, CP 09, 13418-900, Piracicaba, SP, Brazil.
Cranfield Soil and AgriFood Institute, Cranfield University, Cranfield, MK43 0AL, UK.
Ann Bot. 2023 Dec 30;132(7):1233-1248. doi: 10.1093/aob/mcad150.
Gigantism is a key component of the domestication syndrome, a suite of traits that differentiates crops from their wild relatives. Allometric gigantism is strongly marked in horticultural crops, causing disproportionate increases in the size of edible parts such as stems, leaves or fruits. Tomato (Solanum lycopersicum) has attracted attention as a model for fruit gigantism, and many genes have been described controlling this trait. However, the genetic basis of a corresponding increase in size of vegetative organs contributing to isometric gigantism has remained relatively unexplored.
Here, we identified a 0.4-Mb region on chromosome 7 in introgression lines (ILs) from the wild species Solanum pennellii in two different tomato genetic backgrounds (cv. 'M82' and cv. 'Micro-Tom') that controls vegetative and reproductive organ size in tomato. The locus, named ORGAN SIZE (ORG), was fine-mapped using genotype-by-sequencing. A survey of the literature revealed that ORG overlaps with previously mapped quantitative trait loci controlling tomato fruit weight during domestication.
Alleles from the wild species led to lower cell number in different organs, which was partially compensated by greater cell expansion in leaves, but not in fruits. The result was a proportional reduction in leaf, flower and fruit size in the ILs harbouring the alleles from the wild species.
Our findings suggest that selection for large fruit during domestication also tends to select for increases in leaf size by influencing cell division. Since leaf size is relevant for both source-sink balance and crop adaptation to different environments, the discovery of ORG could allow fine-tuning of these parameters.
巨人症是驯化综合征的一个关键组成部分，该综合征是一组区别作物与其野生亲缘关系的特征。在园艺作物中，异速巨人症表现得非常明显，导致茎、叶或果实等可食用部分的大小不成比例地增加。番茄（Solanum lycopersicum）作为果实巨人症的模型引起了人们的关注，已经描述了许多控制这种特征的基因。然而，导致与等速巨人症相关的营养器官大小增加的遗传基础仍然相对未知。
在这里，我们在来自野生种 Solanum pennellii 的导入系（ILs）中鉴定出 7 号染色体上的一个 0.4-Mb 区域，这些 ILs 来自两个不同的番茄遗传背景（cv. 'M82' 和 cv. 'Micro-Tom'），控制番茄营养和生殖器官的大小。该位点命名为器官大小（ORG），使用基因型测序进行精细定位。文献综述表明，ORG 与以前映射的控制番茄果实重量在驯化过程中的数量性状位点重叠。
来自野生种的等位基因导致不同器官的细胞数量减少，但在叶片中通过更大的细胞扩张得到部分补偿，但在果实中没有得到补偿。结果是在携带野生种等位基因的 ILs 中，叶片、花和果实的大小成比例减少。
我们的研究结果表明，在驯化过程中选择大果实也倾向于通过影响细胞分裂来选择叶片增大。由于叶片大小与源库平衡和作物适应不同环境都有关，因此发现 ORG 可以微调这些参数。
