Flavan-3-ols are the major
flavonoids present in
tea (Camellia sinensis) leaves. These are known to have
antioxidant and
free radical scavenging properties in vitro.
Flavanone 3-hydroxylase is considered to be an important
enzyme of
flavonoid pathway leading to accumulation of flavan-3-ols in
tea. Expression analysis revealed the upregulation in transcript levels of C. sinensis
flavanone 3-hydroxylase (CsF3H) encoding gene under salt stress. In this study, the biotechnological potential of CsF3H was evaluated by gene overexpression in tobacco (Nicotiana tabacum cv. Xanthi). Overexpression of CsF3H
cDNA increased the content of flavan-3-ols in tobacco and conferred tolerance to salt stress and fungus Alternaria solani
infection. Transgenic tobaccos were observed for increase in primary root length, number of lateral roots,
chlorophyll content,
antioxidant enzyme expression and their activities. Also, they showed lesser
malondialdehyde content and
electrolyte leakage compared to control tobacco plants. Further, transgenic plants produced higher degree of
pectin methyl esterification via decreasing
pectin methyl
esterase (PME) activity in roots and leaves under unstressed and
salt stressed conditions. The effect of flavan-3-ols on
pectin methyl esterification under
salt stressed conditions was further validated through in vitro experiments in which non-transgenic (wild) tobacco seedlings were exposed to salt stress in presence of flavan-3-ols,
epicatechin and
epigallocatechin. The in vitro exposed seedlings showed similar trend of increase in
pectin methyl esterification through decreasing PME activity as observed in CsF3H transgenic lines. Taken together, overexpression of CsF3H provided tolerance to salt stress and fungus A. solani
infection to transgenic tobacco through improved
antioxidant system and enhanced
pectin methyl esterification.