NtSUS2 silencing alter the topology and the connectivity
of the guard cell metabolic network during dark-to-light transition
We next evaluated the effect of NtSUS2 silencing on guard cell
metabolism at metabolic network level, in which metabolites are the
nodes and the link is the strength of the connection among them,
determined by Pearson correlation coefficient (-0.5 >r > 0.5). Correlation-based networks demonstrate
that light imposition changed substantially the topology and the
connectivity of the networks, with opposite trends observed between WT
and the transgenic lines (Figures 7A-F). Guard cell WT metabolic network
changed from a highly integrated and connected network under dark
condition to a less connected and fragmented network in the light
(Figure 7A-B). This is evidenced by the 2.2-fold higher network density,
the higher average number of links and the lower number of both
connected components and isolated nodes in WT in the dark, when compared
to WT in the light (Table S1). Furthermore, WT metabolic network was
1.4-fold and 1.5-fold more connected than L3 and L13 metabolic networks
in the dark, respectively. By contrast, L3 and L13 metabolic networks
were respectively 1.3-fold and 1.9-fold more connected than WT in the
light (Figures 7A-F; Table S1).
Another clear difference observed among WT and transgenic lines is
related to the heterogeneity of the network, a topological
characteristic of complex networks (Jeong et al., 2000; Pinheiro &
Hartmann, 2017). Higher heterogeneity value reflects the tendency of the
network to have few nodes highly connected (Doncheva et al., 2012). This
parameter is lower and higher in WT than both transgenic lines under
dark and light conditions, respectively (Table S1), indicating that few
nodes have high degree of connection in WT in the light. We next
evaluated the appearance of new hubs and the preferential attachment in
each genotype during dark-to-light transition. A hub-like node was
considered as those with number of links above the average of the
network under dark condition within each genotype. The number of
hub-like nodes dropped from 22 to 3 in WT and from 25 to 17 in L3,
whilst L13 increased from 28 to 37 after dark-to-light transition (Table
S1). The preferential attachment was substantially different between the
genotypes, in which WT, L3 and L13 have respectively 1, 9 and 26 nodes
with higher number of links in the light than the average found in the
respective genotype in the dark. Furthermore, the number of new hubs
that appeared in the light is also higher in the transgenics, in which
2, 8 and 11 new hubs were found in WT, L3 and L13, respectively (Table
S1).