NectarGland: the genetic dance of flowers for pollinators

Research Article published on 28 September 2023 , Updated on 28 September 2023

Led by a team at the Institute of Plant Sciences Paris-Saclay (IPS2 - Univ. Paris-Saclay, French National Research Institute for Agriculture, Food and Environment (INRAE), National Centre for Scientific Research (CNRS), Univ. Paris Cité, Univ. of Évry), the NectarGland project is dedicated to studying the genes and mechanisms involved in nectar production in flowers. Its aim is to develop plants that offer nutritional rewards adapted to the specific needs of pollinators. 

Summer is drawing to a close, but the flowers are still blooming, taking advantage of the last rays of sunshine to perfume the air. With them, the eyes of seasoned observers see a whole ballet of bees and butterflies, attracted by the nectar secreted by the plants. Nectar, produced by specific glands on the plant, is a valuable source of food for insects. Composed of carbohydrates such as glucose, fructose and sucrose, it provides them with the energy they need to survive. It is also the trick plants have developed to guarantee their reproduction through pollination by attracting more pollen-gathering insects. 

However, while the scenario is well known, less is understood about the genes responsible for nectar production in plants. Spearheaded by Abdelhafid Bendahmane, a geneticist specialising in plant improvement at the Institute of Plant Sciences Paris-Saclay (IPS2 - Univ. Paris-Saclay, INRAE, CNRS, Univ. Paris Cité, Univ. d'Évry), the NectarGland project seeks to understand the genetic mechanisms behind pollinating insects' attraction to plant nectar and the reward phenomenon. Supported by an ERC Advanced Grant 2022, the project aims to develop plants offering nutritional rewards adapted to the specific needs of the insects. The main objective is to promote a sustainable approach to the genetic improvement of crops and foster a harmonious coexistence between agriculture and pollinator biodiversity. 

 

Floral forms and agriculture

When it comes to agriculture, the shape of the fruits and vegetables produced is of paramount importance. Breeders prefer shapes that correspond to consumer preferences or agronomic requirements. "In the supermarket, you see cucumbers that are straight, whereas previously cucumbers were crescent-shaped and rarely straight. This meets both marketing and utilitarian demands, as it's easier to store straight cucumbers in boxes, for example," explains Abdelhafid Bendhamane.

Fruits and vegetables, including cucumbers, are the result of the sexual reproduction of plants, in which insects play an essential role. For example, when a bee gathers nectar, pollen grains from the flower's male organs (stamens), containing male reproductive cells, are deposited on its legs. The insect then transports these pollen grains to another flower, where they are deposited on the pistil, the flower's female organ, and fertilise the female reproductive cells it contains. This fertilisation will produce a fruit that contains seeds.  "Insect pollination is essential for the flower to develop into fruit. The seeds that develop inside the fruit can be considered the plant's future babies," explains Abdelhafid Bendhamane. Fruit shape is also closely linked to flower shape.

However, any alteration in flower shape can potentially affect pollination and compromise plant reproduction. For example, if pollinating insects have difficulty accessing the flower's nectar, their visit will be compromised, as will fertilisation. Indeed, pollen, as the carrier of male reproductive cells, plays a crucial role in the reproduction process, while the nectar is a sweet reward offered to pollinators to encourage them to carry pollen from one flower to another. What's more, pollinators often have morphologies specifically adapted to flower shapes, which means that any modifications to the flowers would exclude and penalise certain pollinator species. 

 

From flower sexing to innovative hybridisation

In a previous project, SexyParth, Abdelhafid Bendahmane and his team worked on the genetics of flowers, focusing on sex determination. Although flowers are usually hermaphroditic (possessing both male and female organs), the IPS2 scientists set out to produce distinct male and female flowers. They then noticed reproductive problems related to bees. The cause was a number of factors affecting bees' crucial role as pollinators. Habitat loss, pesticide use, disease and parasites, climate change and competition with invasive species are all contributing to the decline in bee populations, thereby compromising plant pollination.

This is also true for cucurbits, including melons, which depend on pollinators for efficient reproduction. Fruit and vegetable development is compromised by the absence of pollen transport from male to female flowers by bees. Pollination fails, and no fruit or vegetable grows, jeopardising human food diversity and associated practices and crops. A new project led by Abdelhafid Bendahmane and his team, HybridSeed, supported by an ERC "Proof of concept" grant, now aims to put the fundamental knowledge acquired about flower sex into practice, by creating plant prototypes. HybridSeed and NectarGland will be launched in parallel in January 2024, with respective durations of eighteen months and five to six years. 

 

A more sustainable approach to genetic improvement 

Despite its crucial role in attracting pollinators, nectar can also carry diseases, whether through contact with infected pollinators or the presence of pathogens such as bacteria, fungi or viruses. For plants, it's a question of ensuring their reproduction while avoiding contaminating their pollinators. "During the process of human domestication of plants, certain characteristics have been lost, particularly in nectar, which contains metabolites essential for bee health. While we've improved fruit to make it more nutritious for humans, we need to ask whether the rest of the flower is still nutritious for pollinators," stresses Abdelhafid Bendahmane.

Bringing together experts in genetics, molecular biology, artificial intelligence and microscopy, NectarGland will focus on the development of plant glands and nectar production at the cellular level. The ultimate objective is to improve plants so that they meet the specific needs of bees and other pollinators by reintroducing any lost characteristics.

By providing breeders with a toolbox, the project aims to integrate plants harmoniously into agro-ecological systems, while taking into account their impact on pollinator biodiversity. The expected economic and social benefits are positive, not only the creation of businesses but also training for young researchers specialising in this crucial field of study for pollinator preservation.

 

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