Ripening Mutants - Fruit Ripening: Physiology, Signalling and Genomics - page 254

15 Ripening Mutants

Cornelius S. Barry*
Department of Horticulture , Michigan State University , MI , USA

15.1 Introduction

insights into the genetic factors that control
fruit ripening and quality have come from
the characterization of mutants that inhibit
or modify the ripening process, together
with the identifi cation of the underlying
genes. This chapter highlights recent
research on the characterization of ripen-
ing mutants and their impact on our
current understanding of the ripening
process. In compiling topics, a broad
perspective on what defi nes a ripening
mutant has been adopted so as to en-
compass mutants that infl uence different
aspects of ripening and fruit quality. In
addition, while the majority of the chapter
is focused on advances using tomato as a
model system, where appropriate, research
describing fruit-related mutants in other
species is presented.

Fleshy fruits are botanically and
chemically diverse, yet ripening processes
are surprisingly conserved and often
include changes in colour and cell-wall
dissolution, together with subsequent fruit
softening, the synthesis of aroma com-
pounds and conversion of starch to sugars.
These changes increase palatability and
help to signal seed maturity, facilitating
dispersal by frugivores. Due to the
importance of fl eshy fruits in providing
sources of sugars, vitamins, minerals,
antioxidants and fi bre to the human diet,
considerable research effort has focused on
identifying the processes, enzymes and
regulatory proteins that contribute to the
development and ripening of fl eshy fruits
yet limit their postharvest deterioration. In
recent years, the development of genomics
resources for fl eshy fruit-bearing species,
including available genome sequences,
large expressed sequence tag collections
and publically available gene expression
data, have greatly increased our under-
standing of the genes correlated with
events that occur during the ripening
process. However, despite the development
of these resources, functional analyses of
putative ripening-related genes is the main
factor limiting understanding of the
ripening process. While gene-silencing
approaches are useful in some fruit crop
species, some of the most signifi cant

15.2 Ripening Mutants Defi ne Master
Transcriptional Regulators of the
Ripening Process

Mutations at the ripening inhibitor ( rin ),
non-ripening ( nor ) and Colorless non-
ripening ( Cnr ) loci result in dramatic
inhibition of the characteristic phenotypes
associated with ripening, including
respiratory climacteric, ripening-related
ethylene synthesis, chlorophyll deg-
radation, carotenoid biosynthesis, soften-
ing and aroma formation (Robinson and
Tomes 1968; Tigchelaar et al. , 1973, 1978;