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in Arabidopsis enhanced drought and salinity tolerance
(Xu et al., 2012). Different genes encoding for transcrip-
tion factors (TFs) were also highly modulated in Lotus
japonicum under drought stress (Betti et al., 2012).
Interestingly, while a NAM, ATAF1/2 and CUC2 (NAC)
domain TF orthologue to Arabidopsis NAC47 was highly
induced, RAD-like 5 (AtRL5), a gene related to the
myeloblastosis (MYB) family of TFs, was the most
repressed under drought stress in L. japonicum . RAD-like
TFs are a subfamily of the MYB factors. Members of the
RAD-like family of TFs are involved in floral development
in Arabidopsis (Baxter et al., 2007). However, the exact
role of AtRL5 is unknown.
Ge et al. (2010) demonstrated that cell structure, pro-
tein synthesis, energy and secondary metabolism genes
were significantly affected by the alkaline stress
treatment in soybean leaf. The responses of soybean to
NaHCO 3 highlight specific transcription factors, such as
the C2C2-CO-like, MYB-related, WRKY, GARP-G2-like
and ZIM families. Co-expression genes were involved in
regulation of transcription factors, including AP2-EREBP,
bHLH, MYB/MYB-related, C2C2-CO-like, C2C2-DOF,
C2C2, C3H and GARP-G2-like transcription factors. In
this study, it was revealed that ABA-mediated signalling
participates in signal transduction in the alkaline stress
response.
Numerous studies of legume transcriptomes are being
carried out, but a comprehensive analysis of ABA medi-
ation of stress-responsive genes during various stages of
the legume life cycle under different abiotic stresses is
not yet available.
that ABA plays a central role as modulator of many
morpho-physiological responses that help legumes to
survive abiotic stresses. Both the production and catab-
olism of ABA are delicately stress-regulated. Indeed,
such regulation indicates that ABA can act as a stress
signal in legumes when abiotic stress modifies their
growth.
The challenge for plant researchers will be to investi-
gate multiple signalling components in stress tolerance
in agronomically important legumes, thus improving
the yield potential, particularly in areas with adverse
environmental conditions.
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10.9 Concluding remarks
and future prospects
Several environmental factors, including drought,
salinity, nutrient availability and temperature,
adversely affect plant growth and development of a
crop. The need for a change in focus in plant abiotic
stress research has become apparent. This chapter
summarizes our current understanding of the role of
ABA as a key phytohormone controlling different
processes during plant life cycles under abiotic condi-
tions. In this regard, recent progress in plant molecular
biology has shown that a large group of genes are
involved in plant stress responses. Although not all of
these gene expressions are ABA-dependent, it is certain
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