Abiotic Stress Adaptation: Protein Folding Stability and Dynamics - Abiotic Stress: Plant Responses and Applications in Agriculture - page 16

5. Biotechnology approaches for improved abiotic stress tolerance in
plants
Abiotic stress is one of the major causes of crop loss worldwide and restricts certain areas
from productive agriculture and even less severe stress makes plants more susceptible to
diseases and pests. As sessile organisms plants are exposed to various stresses during their
lifespan. With increased understanding of the mechanisms of protein stabilization, advances
have been made in genetically engineering more tolerant crop plants.
5.1. Genetically engineering overproduction of osmolytes
Progress is being made in genetically modifying plants to accumulate high amounts of os‐
molytes with the aim to enhance stress tolerance in plants. Transgenic plants have success‐
fully been engineered to accumulate metabolites such as proline, mannitol, glycine betaine
and trehalose, which resulted in increased tolerance to various stresses [55-57]. In addition
to lowering the osmotic potential and assisting in osmotic adjustment, osmolytes act as hy‐
droxyl radical scavengers and protect macromolecular structure. The accumulation of such
metabolites in response to various stresses is a widely distributed phenomenon in the plant
kingdom. Some important crop plants, however, are non-accumulators. Genetically intro‐
ducing mannitol, sorbitol, trehalose or myo -Inositol production in tobacco, Arabidopsis and
rice, all species that do not synthesize these compounds naturally, produced enhanced toler‐
ance to salt and drought stress [58-60].
Recently, it has been shown that overexpression of rice ( Oryza sativa ) choline monooxyge‐
nase (OsCMO), the first enzyme in glycine betaine biosynthesis, enhances glycine betaine
synthesis in transgenic tobacco plants and resulted in elevated tolerance to salt stress [61].
Although rice has been considered as typical non-accumulator of glycine betaine, this study
revealed that the rice containing ortholog of CMO was fully functional in tobacco species.
Enhanced tolerance toward salinity, heavy metal, oxidative stress and cold stress was also
reported for transgenic tobacco plants when overexpressing rice cystathionine β-synthase
[62] or cold regulated protein CbCOR15b transferred form Capsella bursa-pastoris [63]. Nu‐
merous reports show that introducing and enhancing abiotic stress tolerance by the transfer
of one or more stress responsive genes between species would be an effective strategy to en‐
hance performance of crop plants in less-productive agricultural areas.
Another strategy for osmolyte overproduction and enhaced plant growth relies on site-di‐
rected mutagenesis. Δ 1 -Pyrroline-5-carboxylase synthase (P5CS), which is feedback inhibited
by proline, has been mutated by site-directed mutagenesis, resulting in enzymes that were
no longer inhibited. Plants expressing the mutated enzyme had twice the proline levels of
WT-plants and exhibited increased tolerance to salt stress [64].
5.2. Protein engineering
Protein engineering approaches are being developed for the selection of protein mutations
that increase protein stability. New stabilization strategies are based on random mutagene‐