图1. 豆科SHR-SCR模块决定根皮层细胞分裂及被根瘤菌侵染的命运
(A) 根瘤器官发生与根瘤菌侵染是共生固氮中两个相互协调的基本过程, 图中显示蒺藜苜蓿根瘤纵切面(方括弧示根瘤主体细胞来自皮层, 只有这些细胞(以及表皮细胞)可以被根瘤菌侵染; 箭头示根瘤菌侵染线(洋红色)); (B) 拟南芥(左)和蒺藜苜蓿(右)皮层中SCR基因表达和SHR蛋白转移的差异。Ep: 表皮层; Co: 皮层; En: 内皮层; Pe: 中柱鞘。红色表示SHR基因在中柱细胞中表达; 绿色表示SCR基因在拟南芥根内皮层和蒺藜苜蓿根的内皮层、皮层及表皮层中表达; 黄色表示SHR蛋白转移到内皮层(拟南芥)以及内皮层、皮层和表皮层(蒺藜苜蓿)。

Figure 1. The legume SHR-SCR module predetermines cortical cell identity for cell division and accommodation of rhizobia
(A) Longitudinal section of a developing Medicago truncatula nodule illustrating coordinated nodule organogenesis and rhizobial infection, which are the two fundamental processes during legume-rhizobial nitrogen fixing symbiosis (Bracket indicates that the majority of nodule cells originates from cortical cell division, and only these cells and the epidermal cells can be infected by rhizobia, arrow indicates root hair, arrowheads indicate rhizobial infection threads (magenta color)); (B) Differential SCR gene expression and SHR protein accumulation between Arabidopsis thaliana (left) and M. truncatula (right). Ep: Epidermis; Co: Cortex; En: Endodermis; Pe: Pericycle. The red indicates SHR expression in pericycle; green indicates SCR expressions in the endodermis of A. thaliana root, and the endodermis, cortex and epidermis in M. truncatula; yellow indicates SHR protein accumulation in the endodermis of A. thaliana, and the endodermis, cortex and epidermis in M. truncatula.