A new study published on 16 April in Nature Communications demonstrates how so-called gene priming plants is used to activate shoot progenitors ― the stem cells in plants that facilitate their the growth and regeneration of new stems and leaves (1). These new findings could lead to novel strategies for improving plant regeneration and growth toward mitigating global food security issues.
Inducing pluripotency: humans versus plants
Normally, cells of mature organisms are already committed and cannot transform into other cells types ― this magic act is reserved for so-called pluripotent cells. Most human cells lose this stem-like quality as they age. Whereas, plant cells maintain their regeneration capacity, which they use to renew, repair, or replace lost or damaged plant tissue.
In humans, pluripotent cells, such as embryonic stem cells, use several types of epigenetic regulation for gene priming. Moreover, induced pluripotent cells can be generated from human cells in the lab. The latter were once adult cells but coaxed into pluripotency using a complex artificial process. However, the same result is achieved much more easily and naturally in plants when triggered by external signals such as hormones and stress.
To learn more about this interesting process, the team of scientists, led by Professor Sachihiro Matsunaga from Tokyo University of Science, turned to Arabidopsis thaliana (Arabidopsis) or thale cress, a small flowering plant often used as a model plant in biology studies.
The epigenetics behind plant regeneration
Epigenetics refers to changes in gene expression — often associated with environmental triggers — that do not change the structure of the underlying DNA sequences. Instead, the modifications are achieved by DNA methylation, which essentially attaches a ‘tag’ onto certain regions of the DNA structure, thereby altering gene expression.
The researchers discovered that plant cells use a unique epigenetic process to acquire pluripotency. This important regenerative capacity relies on demethylase which “primes” certain plant genes which are expressed in the presence of regenerative cues.
The gene priming process first silences certain genes to remove the cell’s “epigenetic memory” creating an intermediate bundle of pluripotent cells called a callus. Later, different genes are activated in the cells allowing the callus to transform into new tissue made up of totally different cell types.
More specifically, they found that demethylation is responsible for the regenerative competency of plants ― removal of a methyl group from the amino acid) of the histone H3 by the LDL3 enzyme. The primed histone demethylation is an epigenetic mechanism that the authors believe could potentially enhance the regenerative capacity of important species used in agriculture and forestry.
A potential strategy for agriculture and forestry?
The demethylation process leads to shoot induction, which eventually leads to the formation of stems and leaves. But importantly, the growth of these new stems and leaves do not require seeds. This means farmers and growers could potentially take advantage of the process to promote greening and help plants grow faster without flowing.
The authors hope the new discovery will contribute to solving the global food shortage problem by increasing productivity of staple grains and vegetable crops in an environmentally friendly way.
(1) Ishihara, H. et al. Primed histone demethylation regulates shoot regenerative competency. Nature Communications (2019). DOI: 10.1038/s41467-019-09386-5