Gravity and the availability of nutrients in the soil determ...

created [InstanceEdit:9916282] Naithani, Sushma, 2024-07-23
dbId 9916264
displayName Gravity and the availability of nutrients in the soil determ...
literatureReference
modified [InstanceEdit:9928314] Naithani, Sushma, 2024-11-13
schemaClass Summation
text Gravity and the availability of nutrients in the soil determine plants? growth and root architecture. Root growth in the direction of gravity (positive root gravitropism) ensures proper root anchorage and facilitates water and mineral absorption. Root gravitropism consists of gravity perception, signal transduction, and the curvature response (root angle formation) in the root elongation zone. At the molecular level, root angle formation is controlled by competing gravitropic and anti-gravitropic offset mechanisms. Here, we summarize the gene interactions and processes involved in root angle formation. Recent studies in barley, wheat, and Arabidopsis have identified two important transcription factors, EGT1 (Fusi et al., 2022) and EGT2 (Kirschner et al., 2021, Guo et al., 2023, and Johnson et al., 2022), that play a role in regulating root angle formation by controlling the expression of expansins and ROS homeostasis. ENHANCED GRAVITROPISM 2 (EGT2) was first discovered in barley (HORVU.MOREX.r3.5HG0447830). The barley egt2 mutant displays a hyper-gravitropic root phenotype (with root angles at least 50% narrower than wild-type plants and an enhanced gravitropic response to gravistimulation (Kirschner et al., 2021). Arabidopsis homolog of EGT2 is AtSAM5 (AT3G07760), and mutants of AtSAM5 also have narrower lateral root angles (Johnson et al., 2022). Thus, EGT2 is likely to be an evolutionary conserved regulator of seminal and lateral root growth angle in monocots and dicots. The rice ortholog of EGT2 is Os12g0514600/ LOC_Os12g32992 and has not been functionally characterized. Based on the functional studies in the Barley and Arabidopsis, we identified rice EGT2 (OsEGT2) and its interactors/targets. Similarly, the ENHANCED GRAVITROPISM1 (EGT1) transcription factor was first identified in barley and wheat. In barley and wheat, EGT1 is shown to counteract the gravitropic machinery?s ability to bend the root, thereby controlling root angle. A loss-of-function mutation in the barley HvEGT1 (HORVU6Hr1G068970) and in wheat TdEGT1 genes resulted in a root phenotype where every root class adopts a steeper angle (Fusi et al., 2022). The rice ortholog of EGT1 is OsTLP8/Os02g0705300 / LOC_Os02g47640. The rice EGT1 ortholog has not been functionally characterized, and we identified OsEGT1 based on gene orthology. Both EGT1 and EGT2 are likely to play a crucial role in controlling root angle through an anti-gravitropic mechanism in plants. EGT1 and EGT2 do not interact with each other or regulate each other?s expression but act in the same pathway and control the expression of expansins and genes involved in ROS homeostasis (Guo et al., 2023; Fusi et al., 2022). Expansins facilitate cell expansion by mediating pH-dependent cell wall (CW) loosening (Samalova et al., 2023). Thus, the downregulation of expansin genes by EGT1 and EGT2 is likely to increase the cell wall stiffness and offset the gravitropic bending. The anti-gravitropic offset mechanisms promote the horizontal spread of roots and help roots absorb nutrients.