In cereal and legume crops, the size of the plant organs, particularly the seed, is closely related to the final yield of the crops. However, the molecular mechanisms underlying organ size control in legumes are still poorly understood.

In a previous study, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) characterized a key regulator F-box protein MINI ORGAN1 (MIO1)/SMALL LEAF AND BUSHY1 (SLB1), which controls plant organ size in the model legume Medicago truncatula.

In a new study published in Physiologia Plantarum, the researchers further explored how the MIO1 protein regulates organ size. They performed a yeast library screening and isolated a potential interactor, MtKIX8, by using MIO1 as the bait.

The interaction between MIO1 and MtKIX8 was confirmed further by Y2H, BiFC, split-luciferase complementation and pull-down assays. Phylogenetic analyses indicated that MtKIX8 was highly homologous to Arabidopsis KIX8, which negatively regulates organ size.

Quantitative reverse-transcription PCR and in situ hybridization showed that MtKIX8 was expressed in most developing organs. They also found that MtKIX8 served as a crucial molecular adaptor, facilitating interactions with BIG SEEDS1 (BS1) and MtTOPLESS (MtTPL) proteins in M. truncatula.

Y2H results showed that MtKIX8 also directly interacted with BS1 and MtTOPLESS (MtTPL), suggesting that MtKIX8 repressed organ size by forming the conserved repressor complex in M. truncatula.

The researchers then tried to verify the gene function of MtKIX8 in M. truncatula. They performed a reverse genetic screening to identify the mutant that harbors the retrotransposon Tnt1 in the MtKIX8 gene locus. They observed that the mtkix8 mutant produced enlarged leaves and seeds. When MtKIX8 was ectopically expressed in Arabidopsis, it rescued the increased organ size phenotype in the kix8 mutant.

The study demonstrated that MtKIX8 played an important and conserved role in regulating organ size, and it would be a promising locus for molecular design breeding in legumes.
"Our study provides a useful target gene for the future genetic improvement of legume forage and crops," said CHEN Jianghua of XTBG.

Contact

CHEN Jianghua Ph.D Principal Investigator

Key Laboratory of Tropical Plant Resources and Sustainable Use, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, Yunnan, China

E-mail: jhchen@xtbg.ac.cn

First published: 22 October 2023