Compound leaves are made up of multiple leaflets, displaying higher complexity and diversity in form. The milestone of compound leaf development is the generation of separate leaflet primordia during the early stages, which involves leaflet initiation and boundary establishment for leaflet separation. It is important to seek what the molecular mechanisms are responsible for regulating and integrating leaflet initiation and boundary formation during compound leaf development. 

In a study published in The Plant Cell, CHEN Jianghua’s team of Xishuangbanna Tropical Botanical Garden (XTBG) characterized a pinnate leaf-pattern mutant pinnate-like pentafoliata2 (pinna2) in Medicago truncatula, phenotypically resembling the previously reported pinna1 mutant. They investigated the role of the generally recognized as safe (GRAS) transcription factor PINNA2 in the control of compound leaf morphogenesis in M. truncatula. 

The researchers adopted the method of gene knockout and functional analysis to study the function of PINNA2. Firstly, they determined the importance of PINNA2 in compound leaf morphogenesis through a gene knockout experiment. Then, they revealed how PINNA2 regulates compound leaf formation by directly binding to the promoter region of SINGLE LEAFLET1 (SGL1) through functional analysis. 

It was found that the novel GRAS transcription factor encoded by the PINNA2 gene is more frequently detected at the organ boundary. When PINNA2 is lost, trifoliate leaves transform into pentaphyllate needles. In addition, PINNA2 directly binds to the promoter region of LEAFY homologous gene SINGLE LEAFLET1 (SGL1), which is a key positive regulator. 

Therefore, PINNA2 is an important GRAS transcription factor that regulates compound leaf formation by directly binding to the promoter region of SGL1. Loss of function of PINNA2 results in a three-leafed transition to a five-leafed needle shape.  

"Our finding provides molecular insights into the coordination of intricate developmental processes underlying compound leaf pattern formation,” said CHEN Jianghua. 

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: 6 February 2024