Table 2. Nine key genes confirmed by Signal-net analysis.

Gene symbol	Gene description	Gene abbreviations	Betweenness Centrality*	Degree*
Potri.015G074100	aldehyde dehydrogenase (NAD+)	ALDH	0.998876	4
Potri.001G145300	pyruvate kinase	PK	0.932210	12
Potri.016G120100	pyruvate decarboxylase	PDC	0.802247	2
Potri.013G058300	glutamate dehydrogenase (NAD(P)+)	GDH	0.766292	8
Potri.014G140900	acetate-CoA ligase	ACAS	0.372846	7
Potri.016G087900	adenylosuccinate synthase	AdSS	0.162921	3
Potri.005G075700	asparagine synthase (glutamine-hydrolyzing)	AS	0.114607	2
Potri.001G278400	asparagine synthase (glutamine-hydrolyzing)	AS	0.114607	2
Potri.004G140800	nitrite reductase	NiR	0.083146	2

*Genes are named according to the newest version of Populus trichocarpa 3.0. Betweenness Centrality measures how correlated a gene is with all other network genes. Degree describes the number of single genes that regulate other genes and represents the size of the cycle node.