An alfalfa leafcutting bee (Megachile rotundata) on an alfalfa flower. Photo credit: Peggy Greb. The image is in the public domain.

An alfalfa leafcutting bee (Megachile rotundata) on an alfalfa flower. Photo credit: Peggy Greb. The image is in the public domain.

Once they begin venturing out to forage, honey bees (Apis mellifera) are fighting the clock. Encountering stresses ranging from insecticides to environmental degradation, their life expectancy can be as little as 1 to 30 days. But little was known about the cellular mechanisms that honey bees – and other bee species – mobilise for protection. ‘Recent declines in many bee species worldwide make it important to better understand how bees as a group respond to stress at the cellular level’, says Jon Snow from Barnard College, USA. Having recently discovered that bees activate one family of proteins, known as the lethal(2)-essential-for-life proteins, to counteract stress, Snow had a hunch that another key protein, glycine N-methyltransferase – which plays a key role in the mechanism that allows animals to alter gene expression in response to stressful situations – could also contribute to protection from stress. But first, he and his colleagues needed to find out whether the gene that encodes the methyltransferase protein is activated when honey bees experience stressful conditions.

The team fed honey bees sugar syrup laced with the toxic compounds, infected another group with a parasite and exposed a final group to high temperatures (35 and 45°C), then checked to see whether the glycine N-methyltransferase gene was activated, to begin producing the enzyme. Sure enough, it was, and when the team checked whether the reaction catalysed by this enzyme – which produces sarcosine, a byproduct of an essential process that contributes to gene expression pattern alteration in response to stress – they found it was working exactly as it should. They concluded that glycine N-methyltransferase is a key enzyme that is activated when honey bees need to be protected from stress. But what about other species of bee? Does glycine N-methyltransferase also participate in offering them protection from stressful situations?

This time, the team turned to a less familiar bee, the alfalfa leafcutting bee (Megachile rotundata), which is distantly related to honey bees, is solitary and does a splendid job of pollinating alfalfa and vegetable crops. Because little was known about how alfalfa leafcutting bees respond to stress, the team first fed the antibiotic tunicamycin to the insect, to find out whether it triggered the same stress response that it activates in honey bees. Having confirmed that it did, they then looked for evidence that the antibiotic activated the lethal(2)-essential-for-life and glycine N-methyltransferase genes, which it did. Not only is glycine N-methyltransferase an essential component of the honey bee stress response but distantly related alfalfa leafcutting bees also depend on it, suggesting that glycine N-methyltransferase is probably a key component of the stress responses of all bee species.

But how does this methyltransferase offer protection from stress? Snow explains that creatures can fine-tune how genes are activated by adding a methyl group (simply a carbon with three attached hydrogens) to specific sites on a gene – a process known as epigenetic modification – and that a molecule called S-adenosylmethionine provides this methyl group that alters gene activation. It turns out that glycine N-methyltransferase regulates the levels of S-adenosylmethionine in a cell, so activating glycine N-methyltransferase directly reduces the amount of S-adenosylmethionine, consequently reducing the amount of methylation on genes, altering the expression of genes that are key for protection from stress, such as toxins and other physical challenges in the environment.

So, Snow and colleagues have revealed that glycine N-methyltransferase is a key player in the mechanisms that protect bees from stress, and it appears that honey bees could teach us a lot about bee health in general.

Kogan
,
H. V.
,
Macleod
,
S. G.
,
Rondeau
,
N. C.
,
Raup-Collado
,
J.
,
Cordero
,
V. A.
,
Rovnyak
,
D.
,
Marshalleck
,
C. A.
,
Mallapan
,
M.
,
Flores
,
M. E.
and
Snow
,
J. W.
(
2024
).
Transcriptional control of a metabolic switch regulating cellular methylation reactions is part of a common response to stress in divergent bee species
.
J. Exp. Biol
.
227
,
jeb246894
.