Pea is the fourth largest edible legume crop in the world, widely cultivated worldwide. Several classic leaf mutants have been identified in peas, including unifoliata (uni), afila (af), tendril-less (tl), cocholeata (coch), stipule reduced (st), etc.
In the 1970s, pea breeders introduced the af mutation to develop "half-tendrilless" pea varieties,characterized by all pinnae transforming into tendril branches but retaining a pair of normal stipules. The af "half-tendrilless" mutation then has been widely used worldwide. However, the AF gene locus has not been cloned so far.
In a study published in Physiologia Plantarum, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) identified the candidate mutant genes for the pea classic mutant afila as PsPALM1a and PsPALM1b, further clarifying how the conserved molecular regulatory module AF-UNI (pea)/MPL1-CaLFY (chickpea)/PALM1-SGL1 (alfalfa) mediates different compound leaf morphogenesis.
Phenotypic statistical analysis of the afila mutant revealed that all the basal side leaves of its compound leaves were transformed into tendril branches, while the tendril structure at the top showed no significant change compared to the wild type.
Molecular analysis showed that the AF gene locus is highly associated with two tandemly arranged PsPLAM1a and PsPLAM1b genes, both encoding Cys(2)His(2) zinc finger protein transcription factors, which are orthologous to the reported PALM1 in thorny alfalfa, MPL1 in chickpea, and POP in columbine.
Further in situ hybridization showed that PsPALM1a and PsPALM1b are specifically highly expressed in the basal leaf primordia of early compound leaf primordia, while they are lowly expressed in the top of the compound leaf primordia (future tendril development area) and stipule primordia. Silencing of PsPALM1a and PsPALM1b genes through virus-induced gene silencing (VIGS) can promote the transformation of basal side leaves into tendrils.
"Our provides new insights into the formation mechanism of compound leaf morphological diversity in nature. It also offers important theoretical guidance and genetic resources for the molecular breeding and genetic improvement of semi-leafless traits in peas,"said HE Liangliang of XTBG.

Contact
HE Liangliang Ph.D
Key Laboratory of Tropical Plant Resources and Sustainable Use, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, Yunnan, China
E-mail: heliangliang@xtbg.ac.cn
First published: 26 April 2024