Agriculture Reference
In-Depth Information
Two putative transcription factors
regulating ripening and fruit development
in tomato by inducing climacteric ethylene
biosynthesis and through ethylene-
independent processes have been deter-
mined as an important fi rst step in
controlling fruit ripening. Isolation of the
Colorless non-ripening
(
Cnr
) locus will
hopefully elucidate the developmental
component of ripening regulation. Under-
standing the relationships among the
Cnr
,
ripening-inhibitor
(
rin
) and
non
-
ripening
(
nor
) gene products will follow.
Emerging genomics tools like ESTs and
expression arrays will also help the
identifi cation of additional novel ripening
regulators and homologous genes in other
species, with evolutionary conservation
established via comparative genomics. A
recent comparison of ripening-related gene
expression in non-climacteric grape with
those of the climacteric tomato identifi ed
ripening-related transcription factor se-
quences from families not previously
associated with ripening. EST content
analysis was used to determine gene
expression levels, and subsets of ripening-
related genes from both species were
compared to predict peptide homology and
identify homologous genes with parallel
expression patterns. Twenty ripening-
related putative transcription factor
sequences were identifi ed in each species.
The three common transcription factor
sequences were members of the MADS-
box, basic leucine zipper domain (bZIP)
and zinc-fi nger families; bZIP and zinc-
fi nger proteins have not previously been
associated with ripening. Functional
characterization of these genes and other
regulatory candidates from ongoing
genomics-based experiments will identify
broadly conserved and species-specifi c
genetic regulators of ripening in the near
future.
by phloem-limited bacteria of the genus
Candidatus
Liberibacter. Symptoms in-
clude blotchy, mottled and variegated leaf
chlorosis, followed by tree decline.
Infected leaves become upright, with leaf
drop and twig dieback at later stages (Bové,
2006). Zinc, magnesium or iron defi ciency
cause similar symptoms, making diagnosis
diffi cult.
Understanding host responses to patho-
gen infection at the molecular level will
help develop novel strategies for early
disease detection and therapy. Next-
generation sequencing was used to examine
the differential expression of a higher
number of transcripts than is possible with
microarrays. Next-generation sequencing
also allowed a deeper analysis of different
applications such as the study of gene
isoforms, splice variants and microRNA.
RNA sequencing provides direct counts of
mRNA from expressed sequences rather
than inferring expression based on
hybridization of fl uorescent molecules.
Next-generation sequencing data can be
used to create specifi c transcriptome
assemblies for annotating genomes and
differentially regulated genes and proteins
analysed with any 'omics' technique.
Early host responses of citrus to
infection with
Candidatus
Liberibacter
asiaticus (CaLas) were examined using
next-generation sequencing (Martinelli
et
al.
, 2012). The deep mRNA profi le was
obtained from fruit peel of healthy and
HLB-affected fruit, followed by pathway
and protein-protein network analysis
qRT-PCR validation of a subset of
HLB-regulated genes. A deep gene
regulatory network was constructed. Gene
set enrichment analysis identifi ed several
pathways signifi cantly affected by HLB,
including the metabolism of starch, sucrose
and
D
-linolenic acid and the synthesis of
phenylpropanoids, fl avonoids, terpenoids
and anthocyanins. Plastid genes involved
in photosynthetic light reactions were
upregulated in symptomatic fruit. The
resultant oxidative stress was linked to
activation of protein degradation and
misfolding. Transcripts for heat-shock
proteins were repressed at all stages of
18.9 Citrus Response to
Huanglongbing Disease
Huanglongbing (HLB) or 'citrus greening' is
a highly destructive citrus disease caused
Search WWH ::
Custom Search