Expression of genes related to auxin biosynthesis, transport and
signaling
Tryptophan
(Trp) is a precursor for auxin (indole-3-acetic acid, IAA)
(Woodward and Bartel, 2005), whose
related genes were shown to be differentially expressed under CT and HT
in post-harvest peach fruits. Although the expression level of
tryptophan synthase alpha chain (TRPA; Prupe.3G144500) was decreased on
day 2 in both treatments
(Figure
5 ),
the
expression level of tryptophan synthase beta chain (TRPB;
Prupe.4G207900) showed a peak on day 2 and reached the maximum on day 7
for the CT condition but not for the HT condition.
The
expression level of another auxin biosynthetic enzyme, indole-3-glycerol
phosphate synthase (IGPS; Prupe.3G196200),
manifested
different trends between HT and CT at early stage. Overall, HT reduces
tryptophan biosynthetic enzyme expression level compared with CT.
Several Trp-dependent pathways, which are generally named after an
intermediate, have been proposed, including indole-3-pyruvic acid (IPA)
pathway, indole-3-acetamide (IAM) pathway, tryptamine (TAM) pathway and
indole-3-acetaldoxime (IAOx) pathway
(Woodward and Bartel, 2005;
Zhao, 2012). In IPA pathway [Trp → IPA
→ IAA], the FPKM value of tryptophan aminotransferase ofArabidopsis(TAA1)
was less than 5 in all samples, but the expression of indole-3-pyruvate
monooxygenase (YUCCA) significantly increased on day 2 at HT. In
IAM
pathway [Trp → IAM → IAA], the amidase (AMI; Prupe.6G327700) had
increased expression at the early stage under both temperatures. In TAM
pathway [Trp → TAM → indole-3-acetaldehyde (IAAld) → IAA], aldehyde
dehydrogenase (NAD+) (ALDH2B7; Prupe.1G255200) under HT showed lower
expression than CT in the whole storage period. To sum up, IPA pathway
is affected most by HT in our work.
The expression patterns of auxin-related genes were evaluated to
understand their responses to HT. It was found that the expression of
auxin influx carrier 1 (AUX1) decreased most on day 2 (Figure
5 ) under both temperature conditions, but auxin efflux carrier
component (Pin-formed, PIN5) had a higher expression level under CT. The
auxin response factor (ARF) genes in group II increased at the later
stage for CT rather than HT condition
(Supplementary
Figure S2 ).
These auxin-responsive genes have been classified into three major
groups:
Aux/IAA,
small auxin-up RNA (SAUR), and Gretchen Hagen 3 (GH3)
(Guilfoyle, 1999;
Liscum and Reed, 2002). Aux/IAAs
were sorted into three groups based
on cluster analysis (Figure 6 ), which bind transcription
factors of ARF family (Supplementary Figure S2 ). Generally, the
genes within Group I were down-regulated with time, while the genes in
Group III showed a higher level of expression in HT fruits
(Figure 6 ). Based on the clustering results, SAUR genes were
divided into four groups which had different responses to CT and HT
(Supplementary Figure S3 ). In addition, the gene GH3.1
(Prupe.6G226100) showed a higher expression level under CT compared with
HT, while the other three members of GH3 gene family (GH3.6,
Prupe.8G248400; GH3.1, Prupe.8G137900; GH3.17, Prupe.1G213200) showed
higher expression levels under CT in the later stage (Figure
5 ).