Recently, a collaboration between Professor Gé Liangfa from the College of Forestry and Landscape Architecture and Professor Huang Wei from the School of Life Sciences at South China Agricultural University has revealed the mechanism behind the formation of spiral pods in Medicago truncatula regulated by MtKIX8. The findings have been published online in Plant Physiology.
Modeling Different Shapes of Pod Morphology
Pods, the fruit of legumes, are formed from a single carpel and play a crucial role in protecting seeds. Throughout evolutionary history, pods have evolved into various shapes to adapt to different seed dispersal mechanisms. Based on morphological characteristics, pods can be roughly categorized into three types: straight pods, twisted pods, and contorted pods. While there have been morphological studies on helical pods, the genetic mechanisms behind them remain unclear. Medicago truncatula, commonly known as barrel medic, is a model legume plant with naturally occurring helical pods, making it an ideal material for studying spiral organ formation.
During the screening for factors involved in organ size regulation, researchers identified a transcription factor, MtKIX8, which interacts with BIG SEEDS 1 (BS1) protein. MtKIX8 is a homolog of Arabidopsis AtKIX8/9, tomato SlKIX8/9, soybean GmKIX8/9, pea PsBIO, and Lotus japonicus LjBIO. This gene is widely involved in the developmental regulation of organ size and internal symmetry in angiosperms.
By screening a mutant library of Medicago truncatula, researchers identified two mtkix8 allelic mutants whose pods fail to form regular and compact helical structures during development, with changes in chirality. Through histological studies, researchers observed significant alterations in cell number, morphology, and size in the region of the pod's ventral suture in the mtkix8 mutants. Further investigation revealed that MtKIX8 is significantly expressed in the ventral suture region of the pod, and it determines the final morphology of the pod by coordinating the growth rates of the ventral and dorsal suture regions.
This study not only uncovers a new function of MtKIX8 but also elucidates a mechanistic model for the formation of helical pods in the Medicago genus.
For more information, please refer to the related paper: https://doi.org/10.1093/plphys/kiae170.
