Plants have developed many strategies for dispersal Seeds widely. Some scatter their seeds with the wind, while others lure animals and birds to eat their seed-filled fruit. And a few rare plants – such as watercress Cardamine hirsuta – evolved for seed shells to explode pushing their seeds in all directions.
In the new study published in PNAS, Angela Hay and colleagues – from the Max Planck Institute for Plant Breeding Research in Cologne, Germany – investigated which genes control the mechanical structure of these exploding seed shells. Their findings reveal an important micronutrient – copper – are essential to produce an accurate lignin pattern in the seed coat. Lignin is an abundant plant polymer found in lignocellulose, the main structural material of plants. It is present in plant cell walls and is responsible for making wood hard.
A hard polymer called lignin (dyed red) is deposited into a precise pattern in the cell wall of the exploding seed coat. The researchers identified three laccase enzymes required to form this lignin. No lignin formed in the cell wall (in blue) when all three genes were removed by CRISPR/Cas9 gene editing. Image credit: Miguel Pérez Antón / MPG
C. hirsuta The seed coat consists of two long valves. When the granules are ready to disperse, these valves quickly separate and roll up, shooting the seeds out over a large area. The secret to the explosive nature of these cases is their unique mechanical design, which features three rigid lignin bars connected by hinges. These hinges are important for releasing the potential energy stored in the housing. To create these hinge structures, lignin is deposited in a precise pattern in a single layer of seed coat cells, known as the endocarp.b.
As Hay explained“The mechanical design that allows these fruits to explode depends on the lignin being placed in a precise pattern within this one layer of cells. We know very little about what controls this pattern of lignin deposition, so we set out to identify the genes that control this process. We found three genes required for cell wall lightening in exploded seed coats. These genes code for enzymes, called chains, that polymerize lignin. When C. hirsuta plants that lack all three laccase genes, they also lack lignin in this specific cell type.”
The team also discovered another gene, called SPL7, which is essential for C. hirsuta seed coat evaporation. This gene encodes a protein that regulates copper levels in plants. The researchers detected SPL7 in a mutant screen. Mutant plants lacking this gene, also lack lignin in endarpb Cell wall. Without lignin, they could no longer disperse seeds widely. These effects were reversed when the SPL7 mutants were grown on soils with high copper content, but not when they were grown on soils with low copper content. SPL7, therefore, helps C. hirsuta Plants obtain enough copper to fully develop seed coat, especially when copper levels are low.
But how does copper affect the mechanical structure of these exploding seed shells?
Interestingly, the envelopes are copper-binding proteins that depend on copper for their function. “The link between these two findings is copper,” Hay said. “Plants need SPL7 to cope when there is too little copper in the soil and the envelopes need copper binding for their enzymatic activity. Since lignin is important for the seed coat detonation mechanism and the shells require copper to regulate this evaporation, this makes particle dispersion dependent on the control of copper levels by SPL7. “
These findings provide important new insights into the genes and cellular processes that produce these distinctive explosive structures. They also shed light on the role copper plays in this process and the chemical process itself, which is still poorly understood. One reason for this is the large gene families involved in lignin polymerization in plant cell walls. Figuring out how each gene is involved is therefore challenging, but one of the problems can be solved using the approaches reported in this study, such as tuning. CRISPR/Cas9 gene editing and conditional gene expression.
Copper deficiency in the soil affects plants and trees in a variety of ways and is addressed by the use of copper fertilizers. This is a particular problem for forestry, as low copper levels can weaken trees through poor evaporation. “Our work induces a molecular link between copper and lignin via SPL7 and the envelope. These insights can inspire new approaches to sustainable forest management,” Hay explains.
These findings could also be important for more sustainable biofuel production in the future. Liquefied cell walls pose a challenge to biofuel production because they are resistant to degradation and therefore need to be disrupted using expensive and energy-intensive pretreatment. quantity. Hay notes, “Our work identifies three envelopes that control evaporation in a specific cell type. Understanding the genetic control of lignin polymerization across different cell types and plant species may open new limits to cell wall engineering-based bioenergetics.”
Source: MPG
