3.4 Tiller genes displayed a more wide-scale
change by eCO2 than by N application
rate
To elaborate their responses to eCO2 and N application
rate, we extracted the transcription data of 65 tiller-related genes
from the transcriptome. Among the 51 genes that showed decent expression
(FPKM>0.1) in leaf and/or SAM at 4th true
leaf emerging stage, there were 50 genes varied between tissues (leaf
and SAM), 29 genes being altered by [CO2], and 24
genes being significantly affected by N application (Table 1). This
further corroborated that tissue type (organ) predominantly defines the
gene expression profile. However, as there were more tiller genes being
responsive to [CO2] than N application, the
[CO2] was more influential in regulating the
tiller-related genes than the N application. Of the 29
[CO2] responsive tiller-genes and 24 N application
responsive tiller-genes, there were 16 genes being commonly responsive
to both factors. Eight out of the 22 (36.4%) tiller genes were not
responsive to [CO2] but to N application, whereas 13
out of 27 (48.1%) tiller genes were not responsive to N but to
CO2. This further supported that the
[CO2] was more effective in specifically altering
tiller-related genes than the N application, contrary to their
differential influences to the global transcriptomic profile.
The relative FPKM changes of these tiller genes introduced by N
application (N10/N0), and by [CO2]
(eCO2/Ambient) in different tissues were shown in Table
2. N application caused more dramatic change in the leaf than in the
SAM: 14 (7 up, 7 down) and 12 (11 up, 1 down) tiller genes surpassed
two-fold threshold to be DEG under the ambient and the
eCO2 conditions in the leaf, respectively. In the SAM,
these numbers were three (all down) and 0 for the ambient and
eCO2, respectively. Direct comparison of the
[CO2] effect showed that 16 (8 up and 8 down) and
seven (down) tiller-genes surpassed two-fold in leaf at N0 and N10,
respectively; while these values were seven (6 up and 1 down) and two
(up) in SAM. These indicated that either most of them were not
participating in the tillering response to eCO2, or the
scale of change did not need to surpass the two-fold to affect
tillering. This also implies that other genes might be involved in
tillering promotion in response to eCO2.