Geoscience Reference
In-Depth Information
environmental stress-signalling pathway during climate change,
they extensively investigated
A. thaliana, Oryza sativa
,
Zea
mays
,
Solanum lycopersicum
,
Triticum
, legumes and many other
plants (Zhu, 2001; Bruce et al., 2002; Seki et al., 2003; Baena-
Gonzalez and Sheen, 2008; Becana et al., 2010; Walley and
Dehesh, 2010; Chew and Halliday, 2011; Dolferus et al., 2011;
Santos et al., 2011; Sun et al., 2011; Zhang et al., 2011; Krasensky
and Jonak, 2012). The variety of signalling pathways that play a
central role during plant stress response are auxin (Popko et al.,
2010), abscisic acid (ABA) (Guo et al., 2011; Qin et al., 2011),
brassinosteroids (BRs) (Mussig et al., 2006), cytokinin (Ha et al.,
2012), ethylene (Etheridge et al., 2005; Zhu and Guo, 2008), gib-
berellic acid (GA) (Gao et al., 2011), jasmonic acid (JA) (Balbi
and Devoto, 2008; Wasternack and Kombrink, 2010), salicylic
acid (SA) (Yuan and Lin, 2008; An and Mou, 2011) and nitric
oxide (NO) (Gechev et al., 2006; Grun et al., 2006; Qiao and
Fan, 2008). Auxin, cytokinin, GA, ABA and ethylene are well
accepted as five classes of classic plant hormones. More recently,
evidence has accumulated to extend this concept to include BRs,
JA, SA and NO (Santner and Estelle, 2009). These signalling
molecules not only maintain the development and growth of the
plant but are also helpful in providing the tolerance to the plant
during a change in environmental conditions.
Auxin
Auxin is a phytohormone, which regulates plant developmental
and physiological processes, such as tropic responses to light
and gravity, general root and shoot architecture, embryogene-
sis, vascular differentiation and organogenesis (Woodward and
Bartel, 2005). Genome-wide analysis studies show that the tran-
scriptional response to an auxin is rapid and broad, influencing
the gene expression of a large and different sets of genes (Goda
et al., 2004; Okushima et al., 2005; Overvoorde et al., 2005;
Nemhauser et al., 2006). Recent studies manifest that auxin
homeostasis directly links growth regulation with stress adap-
tation responses. Auxin signalling was controlled at the level
of gene expression by three gene families,
Aux/IAAs (indole-3-
acetic acid), GH3s
and small auxin-up RNAs (
SAURs
). W ES1
(a GH3
protein
) controlled the endogenous auxin (IAA) con-
tent through feedback regulation.
WES1
is the gene expression
increased by environmental stresses as well as by SA and ABA,
causing the reduction of endogenous IAA and resultant growth
retardation under stress conditions, which may provide an adap-
tive strategy on stressed plants (Park, 2007; Park et al., 2007).
Auxin, in conjoining with ABA, regulates the gene expression
R2R3-type MYB transcription factor, MYB96. MYB96, in
