Newly discovered gene function could lead to improved and more productive plant varieties

A research group of the Institute of Plant Molecular and Cellular biology (IBMCP), mixed centre of the Polytechnic University of Valencia (UPV) and the Spanish National Research Council (CSIC), has verified that the SUPERMAN gene also determines the number of flowers in leguminous plants. The finding, which culminates decades of study and has been published in the latest issue of The Plant Journal, opens the door to use them to improve existing and to obtain new, more productive varieties.

The discovery culminates decades of work of the IBMCP team and has been published on the front page of the latest issue of The Plant Journal.

Leguminous plants are a large group of highly important plants due to their nutritional value for humans and cattle. Leguminous plant families are characterised by some distinctive features, such as their compound inflorescence or their complex floral development. “To better understand these characteristics, it is important to study the key regulatory genes involved in the development of inflorescence and the flowers,” explains Luis Cañas, principal investigator of the IBMCP-CSIC project.

The SUPERMAN (SUP) gene is an active repressor that controls the amount of stamen (male reproductive organs) and carpels (female reproductive organs) in Arabidopsis thaliana, the plant used as a model for this type of studies. SUP controls the expression of the genes that will produce the stamen in the third whorl, acting as a barrier and preventing it from reaching the fourth whorl, where the carpel will develop.

“If the SUP gene suffers a mutation and becomes inactive, said genes will also be expressed in the fourth whorl, creating more stamen at the centre of the plant,” says Edelín Roque, researcher of the IBMCP who took part in this project. “Hence the name SUPERMAN, as the mutant plants have more male organs than regular ones.”

The work conducted by the IBMCP group, which is part of the doctoral thesis of Ana Lucía Rodas, intended to obtain the functional characterisation of the SUP gene in the leguminous plant model Medicago truncatula, named MtSUP. To do so, they used mutagenesis through the insertion of retrotransposon Tnt1, genetic editing using CRISPR/Cas9, genetic expression analyses and gene supplementation and overexpression trials. “Our results show that MtSUP shares some roles described for SUP in Arabidopsis, with some variations,” adds Ana Lucía Rodas.

The main novelty is that, in leguminous plants, MtSUP controles the establishment of the secondary inflorescent meristem (I2) and the primordium of petals and stamen. When there is a mutation of this gene, new flowers are created instead of a residual vegetative organ called “spike”, akin to a bract and which develops at the side of the flower. Wild inflorescence usually provides one or two flowers and ends with a spike.

In mutant mtsup-1 there are more flowers after meristem I2, which completes its activity by creating a flower instead of the spike. “Thus, MtSUP controls the number of flowers and petals-stamen that produce the common meristem and primordium, respectively,” explains Rodas.

Pioneering research and applications

For José Pío Beltrán, director of the Group of Biology and Biotechnology of flower development of the IBMCP, “this work culminates the research conducted for decades in our laboratory to reveal the set of regulator genes that control the identity of the flower’s organs and of the areas of the flower where they express themselves. As often happens with pioneering research, here we have unveiled a new function of sequence homology of gene SUPERMAN in eudicots.”

According to Beltrán, “this new function affects a very important trait of the inflorescences of leguminous plants: the number of flowers they produce, where MtSUP is the first gene seen to control this trait of agronomic interest.” For Luis Cañas, “good knowledge on the genes that control the floral development and fruition of leguminous plants is important for its genetic improvement and for generating new high-productivity varieties.”

Full article

Rodas A.L., Roque E., Hamza R., Gómez-Mena C., Minguet E.G., Wen J., Mysore S.K., Beltrán J.P. & Cañas L.A. 2021, MtSUPERMAN plays a key role in compound inflorescence and flower development in Medicago truncatula, The Plant Journal 105 (3): 816-830. https://doi.org/10.1111/tpj.15075