|
Differential expression of three RSus genes encoding sucrose
synthase in the rice were investigated during seed
germination by using specific DNA probes and antibodies
specific to individual gene products. In matured rice seeds,
onlylittle amount of SS2 and SS3 proteins could be detected in
endosprems. When seeds were imbibed in water for
germination for 3 days, both RSus1 and RSus2 were expressed
prominentey in embryos. However, the expression levels of both
genes in embryos and etiolated seedlings declined during
seedling development. Experssion of RSus3 was highly specific
to endosprem, the expression products of RSus3 could not be
detected in embryos and etiolated seedlings.
To investigate the effects of sugars on Rsus gene expression,
the excised shoots and roots of etiolated rice seedlings
were incubated for 24 hours in different sugars and a range
of concentrations.The expression level of RSus1 mRNA in
shoots was increased by increased concentration of sucrose,
fructose and glucose. However, the RSus2 mRNA was maximally
increased when the shoots was treated with 0.2%
sucrose, glucose and fructose. In roots, maximally expression
of RSus1 and RSus2 required various optimal concentration of
sugar supplies. At the protein level, the changes in the
abundance of SS1 and SS2 protomers were less pronounced but
consistent with the changes in transcript leve. It
suggested that the expression of RSus genes in response to
sugars was controlled at the transcriptional level.
|