Figure 3.

Phosphorus (P) and nitrogen (N) availability steer root system architecture. (A) Representative cartoon of a cereal root architecture. (B) Auxin response and levels are enhanced in P-deficient roots. The elevated auxin response causes the activation of ARF7 and ARF19 regulating the expression of RSL2 and RSL4 transcription factors, ultimately regulating the root hair elongation. OsARF12 and OsARF15 act as negative regulators of P homeostasis and regulate the branching density and root hair elongation in rice. (C) Root architecture of a low N (nitrogen) stressed plants showing enhanced forging capacity by elongating root hairs, longer branching, and steep root angle. Low N stress increases the IAA level via up-regulating expression of auxin biosynthetic genes. For example, TAR2 expression is increased under low N and results in higher IAA levels, which in turn reshapes the root architecture to favor maximum N uptake. AGL21 also positively regulates the expression YUC5, YUC8, and TAR3, which increases IAA synthesis rate under low N conditions. OsNRT2.1, which acts as an auxin influx facilitator, regulates lateral branching in rice by controlling PIN2 expression.