Daminato Margherita, Masiero Simona, Resentini Francesca, Lovisetto Alessandro, Casadoro Giorgio
BMC Plant Biol. 2014 Nov 30;14:319. doi: 10.1186/s12870-014-0319-y.
The identity of flower organs is specified by various MIKC MADS-box transcription factors which act in a combinatorial manner. TM8 is a MADS-box gene that was isolated from the floral meristem of a tomato mutant more than twenty years ago, but is still poorly known from a functional point of view in spite of being present in both Angiosperms and Gymnosperms, with some species harbouring more than one copy of the gene. This study reports a characterization of TM8 that was carried out in transgenic tomato plants with altered expression of the gene.
Tomato plants over-expressing either TM8 or a chimeric repressor form of the gene (TM8:SRDX) were prepared. In the TM8 up-regulated plants it was possible to observe anomalous stamens with poorly viable pollen and altered expression of several floral identity genes, among them B-, C- and E-function ones, while no apparent morphological modifications were visible in the other whorls. Oblong ovaries and fruits, that were also parthenocarpic, were obtained in the plants expressing the TM8:SRDX repressor gene. Such ovaries showed modified expression of various carpel-related genes. No apparent modifications could be seen in the other flower whorls. The latter plants had also epinastic leaves and malformed flower abscission zones. By using yeast two hybrid assays it was possible to show that TM8 was able to interact in yeast with MACROCALIX.
The impact of the ectopically altered TM8 expression on the reproductive structures suggests that this gene plays some role in the development of the tomato flower. MACROCALYX, a putative A-function MADS-box gene, was expressed in all the four whorls of fully developed flowers, and showed quantitative variations that were opposite to those of TM8 in the anomalous stamens and ovaries. Since the TM8 protein interacted in vitro only with the A-function MADS-box protein MACROCALYX, it seems that for the correct differentiation of the tomato reproductive structures possible interactions between TM8 and MACROCALYX proteins might be important.
花器官的身份由多种以组合方式起作用的MIKC MADS盒转录因子决定。TM8是一个MADS盒基因，二十多年前从番茄突变体的花分生组织中分离出来，但尽管在被子植物和裸子植物中都存在，有些物种还含有该基因的多个拷贝，但从功能角度仍知之甚少。本研究报道了在基因表达改变的转基因番茄植株中对TM8进行的特性分析。
制备了过表达TM8或该基因嵌合阻遏形式（TM8:SRDX）的番茄植株。在TM8上调的植株中，可以观察到雄蕊异常，花粉活力差，并且几个花身份基因的表达发生改变，其中包括B功能、C功能和E功能的基因，而其他轮次没有明显的形态改变。在表达TM8:SRDX阻遏基因的植株中获得了长圆形的子房和果实，这些子房也是单性结实的。这些子房显示出各种心皮相关基因的表达改变。在其他花轮次中没有明显的变化。后一种植株还具有叶片偏上生长和花脱落区畸形的特征。通过酵母双杂交试验表明，TM8能够在酵母中与MACROCALIX相互作用。
TM8表达的异位改变对生殖结构的影响表明，该基因在番茄花的发育中起一定作用。MACROCALYX是一个假定的A功能MADS盒基因，在完全发育的花的所有四轮中都有表达，并且在异常雄蕊和子房中显示出与TM8相反的数量变化。由于TM8蛋白仅在体外与A功能MADS盒蛋白MACROCALYX相互作用看来，TM8和MACROCALYX蛋白之间可能的相互作用对于番茄生殖结构的正确分化可能很重要。
