Expression of genes related to ethylene biosynthesis and
signaling pathway
Ethylene is biosynthesized by S-adenosylmethionine synthetase (SAMS)
from the amino acid methionine to S-adenosyl-L-methionine (SAM), and SAM
is then converted by
1-aminocyclopropane-1-carboxylic
acid (ACC) synthase (ACS) to ACC which is further catalyzed by
ACC-oxidase (ACO) to ethylene. Notably, the activity of ACS determines
the rate of ethylene production (Yu et
al., 1979). Similar to ethylene production (Figure 1b ), the
peach fruits at CT were higher than HT in the enzyme activities of ACO
and ACS at most time points (Figure 7 ).
Expressions of genes involved in ethylene biosynthesis and signaling
were examined to understand the lower ethylene production
in
HT fruits. Among these, the expression of 5 genes (SAMS5,
Prupe.1G107000; SAMS1, Prupe.3G004000; SAMS3, Prupe.7G128500; ACS1,
Prupe.2G176900;
ACO1, Prupe.3G209900) were significantly higher at CT than HT
(Figure
8a ), which
agreed
with the physiological data of ACO/ACS activities (Figure 7 ).
Ethylene is
perceived
by a family of five membrane-localized
receptors
that are homologous to bacterial two-component histidine kinases
involved in sensing environmental changes
(Stepanova and Alonso, 2009). According
to the homology with Arabidopsis , four peach ethylene receptors
were identified, including ethylene receptors 1 (ETR1; Prupe.1G556000),
ETR2 (Prupe.1G034300), ethylene response sensor 1 (ERS1; Prupe.8G265200)
and ethylene insensitive 4 (EIN4; Prupe.6G348000). The expression levels
of ETR2 and ERS1 at CT were generally higher than HT, while those of
ETR1 and EIN4 were not obvious (Figure 8b ).
Constitutive
triple response 1 (CTR1; Prupe.7G117700), the downstream element of
ethylene receptors, showed significantly decreased expression on day 2
with an average of 2.69-fold change, and then kept in low FPKM value at
later time points (Figure 8b ). Especially, EIN2
(Prupe.6G235600), whose function is
a
positive regulator of the ethylene pathway
(Stepanova and Alonso, 2009), displayed
reverse trends of expression levels between CT and HT. EIN3
(Prupe.2G058500, Prupe.2G058400) exhibited declining expression level on
day 2. Besides, ERFs were sorted into four groups based on hierarchical
clustering (Supplementary Figure S4a ). Group I showed a higher
level of transcripts in HT condition, indicating that group I genes
might play a significant role in heat stress response
(Supplementary Figure S4b ). Therefore, temperature caused
complicated responses in receptor genes and downstream signaling genes
of ethylene in both CT and HT conditions.
Expression
of genes related
to