Authors: Ai-Ke Bao*, Bao-Qiang Du,
Leila Touil, Peng Kang, Qiang-Long Wang, Suo-Min Wang*
Abstract: Salinity and drought are major environmental factors limiting the growth and productivity of alfalfa worldwide since this economically important legume forage is sensitive to these kinds of abiotic stress. In the present study, transgenic alfalfa
lines expressing both tonoplast NXH and H
+-PPase genes,
ZxNHX and
ZxVP1-1 from the xerophyte
Zygophyllum xanthoxylum L., were produced via
Agrobacterium tumefaciens-mediated transformation. Compared with wild-type (WT),
transgenic alfalfa plants co-expressing ZxNHX and ZxVP1-1 grew better with greater plant height and dry mass under normal or stress conditions (NaCl or water-deficit) in the greenhouse.
The growth performance of transgenic alfalfa plants was associated with more Na
+, K
+ and Ca
2+ accumulation in leaves and roots, as a result of co-expression of
ZxNHX and
ZxVP1-1. Cation accumulation contributed to maintaining intracellular ions homeostasis and osmoregulation of plants and thus conferred higher leaf relative water content and greater photosynthesis capacity in transgenic plants compared to WT when
subjected to NaCl or water-deficit stress. Furthermore, the
transgenic alfalfa co-expressing
ZxNHX and
ZxVP1-1 also grew faster than WT plants under field conditions, and most importantly, exhibited enhanced photosynthesis capacity by maintaining higher net photosynthetic rate, stomatal conductance, and water use efficiency than WT plants. Our results indicate that co-expression of tonoplast NHX and H
+-PPase genes from a xerophyte
significantly improved the growth of alfalfa, and enhanced its tolerance to high salinity and drought. This study laid a solid basis for reclaiming and
restoring saline and arid marginal lands as well as improving forage yield in northern China.
