journal Cell
Salk discovery of novel pathway could be a boon to
agriculture
(December 24, 2015) Despite
seeming passive, plants wage wars with each other to outgrow and absorb
sunlight. If a plant is shaded by another, it becomes cut off from essential
sunlight it needs to survive.
To escape this deadly shade, plants have light sensors that
can set off an internal alarm when threatened by the shade of other plants.
Their sensors can detect depletion of red and blue light (wavelengths absorbed
by vegetation) to distinguish between an aggressive nearby plant from a passing
cloud.
Scientists at the Salk Institute have discovered a way by
which plants assess the quality of shade to outgrow menacing neighbors, a
finding that could be used to improve the productivity of crops. The new work,
published December 24, 2015 in Cell, shows how the depletion of blue light
detected by molecular sensors in plants triggers accelerated growth to overcome
a competing plant.
“With this knowledge and discoveries like it, maybe you
could eventually teach a plant to ignore the fact that it’s in the shade and
put out a lot of biomass anyway,” says Joanne Chory, senior author and director
of Salk’s Plant Molecular and Cellular Biology.
The new work upends previously held notions in the field. It
was known that plants respond to diminished red light by activating a growth
hormone called auxin to outpace its neighbors. However, this is the first time
researchers have shown that shade avoidance can happen through an entirely
different mechanism: instead of changing the levels of auxin, a cellular sensor
called cryptochrome responds to diminished blue light by turning on genes that
promote cell growth.
This revelation could help researchers learn how to modify
plant genes to optimize growth to, for example, coerce soy or tomato crops
(which are notoriously fickle) grow more aggressively and give a greater yield
even in a crowded, shady field.
The focus of the team’s research efforts was cryptochromes,
blue light-sensitive sensors that are responsible for telling a plant when to
grow and when to flower. Cryptochromes were first identified in plants and
later found in animals, and in both organisms they are associated with
circadian rhythm (the body’s biological clock). The protein’s role in sensing depletion
of blue light had been known, but this study is the first to show how
cryptochromes promote growth in a shaded environment.
The team placed normal and mutant Arabidopsis plants in a
light-controlled room where blue light was limited. The mutant plants lacked
either cryptochromes or a PIF transcription factor, a type of protein that
binds to DNA to control when genes are switched on or off. PIFs typically make
direct contact with red light sensors, called phytochromes, to initiate shade
avoidance growth. The researchers compared the responses of the mutant and
normal plants in the varying blue light conditions by monitoring the growth
rate of the stems and looking at contacts between cryptochromes, PIFs and
chromosomes.