ABA Metabolism and Signaling in Fleshy Fruits - Abscisic Acid: Metabolism, Transport and Signaling - page 263

during the development and ripening of fleshy fruits have been shown to be regu-
lated by plant hormones. Of these, there has been particular focus on the central role
played the gaseous hormone ethylene in controlling ripening in climacteric fruits,
such as tomato ( Solanum lycopersicum ) (Alexander and Grierson 2002 ; Adams-
Phillips et al. 2004 ; Prasanna et al. 2007 ; Gapper et al. 2013 ; Seymour et al. 2013 ;
Perotti et al. 2014 ). However, there has been a recent increase in the number of stud-
ies that have addressed the roles of other phytohormones in fruit biology, as well as
the extent and nature of hormonal cross-talk. This is exemplified by studies of absci-
sic acid (ABA), which has been demonstrated to play an important role in regulat-
ing the ripening of non-climacteric and climacteric fleshy fruits (Zhang et al. 2009 ;
Gambetta et al. 2010 ; Jia et al. 2011 ; Chai et al. 2011 ; Akagi et al. 2012 ; Sun et al.
2012a , b ; Romero et al. 2012 ; Li et al. 2013 ; Nicolas et al. 2014 ). Indeed, it has been
proposed that, in addition to ethylene, ABA is a fundamentally important regulator
of fruit maturation and senescence (Zhang et al. 2009 ).
It is well established that ABA is extremely important in the adaptation of
plants to adverse environmental conditions, as well as regulating various aspects
of plant growth and development, such as seed/bud dormancy and growth in
both the seedling, and root (Leung and Giraudat 1998 ; Finkelstein et al. 2002 ;
Himmelbach et al. 2003 ; Hirayama and Shinozaki 2007 ; Gapper et al. 2013 ;
Seymour et al. 2013 ; Perotti et al. 2014 ). Moreover, much is now known about the
molecular processes associated with ABA metabolism, signaling and downstream
responses. ABA receptors, which were sought for by scientists for several decades,
have now been identified (Fujii et al. 2009 ; Ma et al. 2009 ; Miyazono et al. 2009 ;
Melcher et al. 2009 ; Nishimura et al. 2009 ; Santiago et al. 2009 ; Shang et al.
2010 ), and studies using the experimental model plant Arabidopsis thaliana have
led to the discovery of two core ABA signaling pathways: ABA-PYR1-PP2C-
SnRK2 (Fujii et al. 2009 ) and ABA-ABAR-WRKY40-ABI5 (Shang et al. 2010 ).
In addition to these breakthroughs in elucidating ABA perception and signal trans-
duction, much progress has also been made toward understanding ABA signal-
ing specifically in fleshy fruits (Zhang et al. 2009 ; Gambetta et al. 2010 ; Jia et al.
2011 ; Chai et al. 2011 ; Akagi et al. 2012 ; Sun et al. 2012a , b ; Romero et al. 2012 ;
Li et al. 2013 ; Nicolas et al. 2014 ). In this review, we summarize some current
ideas and observations regarding the roles of ABA in the regulation of fleshy fruit
development and ripening and, where appropriate, recent insights into the underly-
ing molecular mechanisms.
14.2 Effects of ABA on Fleshy Fruit Development
and Ripening
Earlier studies of the significance of ABA in fleshy fruit development and ripening
primarily targeted the berries of grape ( Vitis vinifera ), a non-climacteric fruit,
where evidence was uncovered of a relationship between ABA and the verai-
son stage of development, which is marked by a berry color change at the onset