3.3 Identification of differentially expressed proteins related
to rice development and quality formation
A total of 748 unique proteins were identified based on their specific
expressions when exposed to high temperature. After removing 302
proteins with lower scores and unknown functional classification, 39
proteins related to rice development and quality formation were
distinguished (Table 2, Figure 6). In this study, the expression of 16.9
kDa class Ⅰ heat shock protein in rice grains was significantly reduced
3 days after heating, which was down-regulated by 84% compared with CK
treatment. However, the expression of heat shock factor binding protein
1 involved in heat shock protein synthesis was significantly increased.
Furthermore, the expression levels of HSP70s at early grain-filling
stages were only about half of normal treatment (0.47, 0.5, and 0.43
times reduction at 3d, 6d 9d after flowering, respectively). Results
showed the most significant change was the 26.7 kDa heat shock protein
of the sHSPs family, and its expression was increased significantly at
6, 9, and 12 days after flowering, with 6.78, 3.06, and 5.44 folds
compared to the CK treatment. At the 12th day after flowering, the
expressions of 18.0kda class II heat shock protein, 24.1kda heat shock
protein and heat shock protein 82 were up-regulated to varying degrees
(2.26, 2.01, 3.63 folds respectively) when subjected to high
temperatures.
Expression of proteins related to rice quality formation were also
regulated under field warming conditions. Expressions of glutelin
anabolism proteins were regulated at the beginning of grain-filling. For
example, the glutelin type-A 3, glutelin type-B 1, glutelin type-B
5-like expression levels of rice grains were significantly up-regulated
by 2.79, 2.49, and 3.3 folds, respectively. At the same time, the
expression levels of glutelin type-B 1-like and glutelin type-B 2-like
proteins were decreased significantly. Furthermore, the expression
levels of globulin 19 kDa globulin, globulin 1s allele and basic 7S
globulin were increased significantly, which is consistent with the
increase of globulin content measured in mature grains. In this study,
the significant decrease in prolamin under warming conditions was mainly
at the 12th day after flowering and expression analysis of prolamin
PPROL 14E and prolamin PPROL 14E-like proteins showed that they were
both decreased significantly (0.33, 0.38 folds) at this stage comparted
to the normal temperature treatment. As the main component of rice
grains, the accumulation of rice grain starch has been proved to be
sensitive to elevated temperature. The synthesis of rice grain starch is
mainly regulated by a series of protein families, including SSS, SBE,
DBE, GBSS. In this study, the GBSS was down-regulated at the 6th day
after flowering under increased temperature. While proteins related to
amylopectin synthesis obtained no significant changes when compared to
the CK. The expression levels of granule-bound starch synthase at 6d, 9d
and 12d after flowering were significantly lower than that of the
control and the expression levels of soluble starch synthase responsible
for the synthesis of amylopectin SS4 and SSS2-3 were decreased under
high temperatures.
Results of this study showed that another key growth and development
process regulated by the increased temperature during grain-filling
stage was the photosynthetic system of rice plant. In this study, the
expression levels of the chlorophyll a-b binding protein 1B-21,
chlorophyll a-b binding protein P4, and chlorophyll a-b binding protein
7 in chlorophyll ab binding protein were significantly up-regulated at
the beginning of grain-filling (2.22, 2.03, 3.3 times), when compared to
the CK. On the other hand, the expression of PSB28, which is responsible
for water splitting, had a downward trend through the grain-filling
period, and reaching a significant level at 12 days after
flowering. Furthermore, protein TIC 62 (translocon at the inner envelope
membrane of chloroplasts) responsible for the dynamic balance of the
proteome was significantly downregulated at 9d after flowering.
Photosynthesis is the process by which light energy is converted into
chemical energy and stored, and thus it is essential for the
accumulation of rice grain assimilation.