| JOINTLESS is a MADS-box gene that plays a key role in tomato flower pedicel abscission zone development. In jointless mutant plants, some inflorescence meristems revert to vegetative growth, their flowering time is slightly delayed, and the sympodial identity of inflorescence meristems is suppressed. However, we still don't know why the lack of the normal JOINTLESS protein has the pleiotropic effects in the mutant's development. Here I report more evidence that JOINTLESS gene is a pleiotropic regulator of tomato growth and development, and it may affect multiple hormone homeostasis in tomato. Compared to wild type plants, jointless mutant plants have larger and heavier seeds and fruits; delayed germination; thicker, longer hypocotyls, stems and hypocotyls cells; and more and longer internodes. Mature jointless plants are also much taller, they have fewer seeds per fruit, and about 30% of the jointless fruits have developed irregular fruit locule structure. These phenotypes are similar to some plant hormone mutants. To determine whether JOINTLESS affects the perception and/or production of plant hormones, dose response experiments were performed on six major plant hormones and some of their inhibitors. The results show that jointless seedlings are more sensitive not only to the external hormones auxin (IAA), ethylene (ACC), gibberellin (GA3), and brassinosteroids (24-eBL), but also to the gibberellin synthesis inhibitor paclobutrazol (PAC) and auxin transport inhibitor N-1-Naphthylphthalamic Acid (NPA). Real-time PCR results show that some key genes involved in ethylene and gibberellin synthesis, auxin signaling and metabolism, and cell wall metabolism are upregulated in the jointless mutant seedlings. I propose that JOINTLESS is involved in regulating the perception and/or production of multiple plant hormones and/or the crosstalk between them, leading to its pleiotropic effects on tomato growth and development in the mutant plants. A model is proposed to explain how JOINTLESS affects the development of tomato flower pedicel abscission zones. This research not only deepens our understanding of the functional mechanism of JOINTLESS, but also furthers our understanding of plant MADS-box genes' functional mechanism in general. At the same time, because JOINTLESS is involved in regulating traits that are important in agriculture such as fruit abscission zone, fruit size, seed size, and plant height, we may be able manipulate these traits genetically by changing the expression levels of JOINTLESS. |
