OsGH3-2 is a GH3 family gene.
- OsGH3-2 encoding an enzyme catalysing IAA conjugation to amino acids, is involved in the modulation of ABA level and stress tolerance.
- OsGH3-2 modulates both endogenous free IAA and ABA homeostasis and differentially affects drought and cold tolerance in rice. OsGH3-2 may contribute to carotenoid metabolism and ABA synthesis, especially at the level of α-carotene and β-carotene metabolism.
- The disruption of OsGH3-2 affected the expression of many ABA synthesis and auxin-related genes, which may have contributed to the different phenotypes under drought and cold stresses.
- Auxin signal transduction pathway, auxin-miR167-ARF8-OsGH3-2, could be, in conjunction with the other microRNA-mediated auxin signals, an important one for responding to exogeneous auxin and for determining the cellular free auxin level which guides appropriate auxin responses.
- The presence of auxin in the medium controlled the level of miR167 and in turn miR167-mediated regulation of ARF8 and OsGH3-2.
- GH3-2 may regulates root development. GH3-2 may be involved in disease resistance. GH3-2 positively regulates rice disease resistance by suppressing pathogen-induced accumulation of IAA in rice. Activation of GH3-2 confers to rice a broadspectrum and partial resistance against Xoo, Xoc, and M. grisea.
- GH3-2 has amido synthetase activity and is more capable of catalyzing the synthesis of IAA-Asp than IAA-Ala.
- A simple model was proposed to explain the increased drought sensitivity and cold tolerance of the OsGH3-2-overexpressing rice (Fig. 1). In contrast to the intensive molecular and genetic research of ABA deficiency related to drought, the function of auxin under cold stress and the balance of auxin and ABA metabolism under cold stress have received limited attention.
- Overexpression of OsGH3-2 causes a decrease in IAA. The decrease in IAA results in a decrease in the ABA level, which further results in decreased expression of some drought-response genes and faster water loss under drought stress conditions. The decrease in IAA also results in reduced numbers of lateral roots and root hairs, which may weaken water uptake. Decreases in IAA may also impair SOD activity. Together, these contribute to the drought sensitivity of OsGH3-2-overexpressing rice(Fig. 1A).
- Overexpression of OsGH3-2 impairs the accumulation of free IAA, leading to enhanced ROS scavenging ability and increased expression of some genes related to cold response and membrane permeability, which ultimately contributes to cold tolerance(Fig. 1B).
- Two OsGH3-2-overexpressing lines :
- D176UM14 at the T4 generation
- They were grown in a field with three biological repeats. Plants at the five-leaf stage were subjected to drought stress. During the stress, the transgenic plants showed drought-stressed symptoms earlier than the WT’. After recovery for several days, the overexpressing lines had a significantly lower survival rate(~20–30%) than the WT’.
- Compared with WT’, the SOD activity in the overexpressing lines was slightly higher before the stress but was significantly lower after the stress. This result was similar to the SOD changes in a carotenoid-ABA-deficient mutant, dsm2, in our previous report, implying that overexpression of OsGH3-2 may impair ROS scavenging under drought stress.
- During the cold stress, the relative penetrability gradually increased but was significantly lower in the OsGH3-2-overexpressing rice than in WT’.
- Under severe drought stress, there was a slight decrease in the free IAA level in the WT’, but overall the OsGH3-2-overexpressing lines contained significantly less free IAA than the WT’ plants.
- Expression of OsGH3-2 was induced by drought but was suppressed by cold. Overexpression of OsGH3-2 in rice caused significant morphological aberrations related to IAA deficiency, such as dwarfism, smaller leaves, and fewer crown roots and root hairs. The overexpressing line showed significantly reduced carotene, ABA, and free IAA levels, greater stomata aperture, and faster water loss, and was hypersensitive to drought stress. However, the overexpressing line showed increased cold tolerance, which was due to the combined effects of reduced free IAA content, alleviated oxidative damage, and decreased membrane penetrability. Furthermore, expression levels of some ABA synthesis- and stress-related genes were significantly changed in the overexpression line.
- OsGH3-2 was expressed in most of the tissues and organs and had relatively high levels in calli, leaves, and roots, and low levels in the panicles and stems. The OsGH3-2 transcript level was rapidly induced by IAA, whereas it was slightly suppressed by ABA. OsGH3-2 expression was induced by drought, with the transcript level increasing to a peak of nearly eight fold on d 3 after the stress was applied. Contrary to our expectations, OsGH3-2 was notably suppressed by cold stress.
- Du et al. also examined the expression of well-characterized auxin signalling genes in the OsGH3-2-overexpressing rice. The mRNA levels of OsIAA20, OsRAA1, and OsSAUR39 were upregulated in OsGH3-2-overexpressing rice, whereas the expression levels of the other genes were unaffected.
- It was also shown that expression of OsGH3-2, an rice IAA-conjugating enzyme, was positively regulated by ARF8. Delivery of synthesized miR167 into cells led to decrease of both ARF8 mRNA and OsGH3-2 mRNA, indicating that ARF8 regulation of OsGH3-2 expression is also conserved in rice as in Arabidopsis.
- To further examine this expression feature, Fu et al analyzed GH3-2 expression in root and stem from rice variety Minghui 63 at the booting (panicle development) stage. Compared with its expression in the other five tissues, GH3-2 showed the highest expression level in root and the lowest expression level in stem.
- Interestingly, GH3-2, -6 and -8 showed greater expression levels in older leaf or flag leaf than in younger leaves in both varieties. GH3-2 and -5 occupied the top two spots in GH3s with the highest expression levels in radicles and root.
- The expression level of the GH3-2 allele from Minghui 63 in R233 was significantly higher than that in Zhenshan 97 before and at some time points after M. grisea infection, whereas the expression level of the GH3-2 allele from Zhenshan 97 in R194 was significantly higher than that in Zhenshan 97 at other time points after infection.
- Among the rice GH3 homologs (OsGH3) to these Arabidopsis genes, the published OsGH3-2 sequence (26)exhibited the highest homology to the Arabidopsis DFL1 counterpart (73% homology at the 390 bp span in blast search).
- Genetic distances were calculated with the Poisson correction method and a phylogenetic tree was constructed with the neighbor-joining method, performing the bootstrap test with 5000 iterations. Rice proteins were only present in groups I and II. Thus, group III, composed exclusively of Arabidopsis proteins may represent a completely new class of GH3 proteins. Different orthologous relationships were detected in this analysis. Orthologous relationships of the n:n kind in group II were observed for AtGH3.1, 2, 3, 4/OsGH3.2, 8, 9, 10 and AtGH3.5, 6/OsGH3.1, 4, suggesting functions that diversified in both species.
- Auxin regulates plant growth and development by altering the expression of diverse genes. Among these, the genes of Aux/IAA, SAUR, and GH3 classes have been extensively studied in dicots, but little information is available on monocots. .
- The rice GH3 proteins can be classified in two groups (groups I and II) on the basis of their phylogenetic relationship with Arabidopsis GH3 proteins. Based upon the sequences available in the database, not a single group III GH3 protein could be identified in rice. An extensive survey of EST sequences of other monocots led to the conclusion that although GH3 gene family is highly conserved in both dicots and monocots but the group III is conspicuous by its absence in monocots. The in silico analysis has been complemented with experimental data to quantify transcript levels of all GH3 gene family members. Using real-time polymerase chain reaction, the organ-specific expression of individual OsGH3 genes in light- and dark-grown seedlings/ plants has been examined..
Labs working on this gene
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, PR China
- Department of Biological Science and the Basic Science Research Institute, Sungkyunkwan University, Suwon, Korea 440-746
- Departamento de Genómica, Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra. Moncada Náquera Km 4,5, Moncada (Valencia) 46113, Spain
- Du H, Wu N, Fu J, et al. A GH3 family member, OsGH3-2, modulates auxin and abscisic acid levels and differentially affects drought and cold tolerance in rice[J]. Journal of experimental botany, 2012, 63(18): 6467-6480.
- Yang J H, Han S J, Yoon E K, et al. Evidence of an auxin signal pathway, microRNA167-ARF8-GH3, and its response to exogenous auxin in cultured rice cells[J]. Nucleic acids research, 2006, 34(6): 1892-1899.
- Fu J, Yu H, Li X, et al. Rice GH3 gene family: Regulators of growth and development[J]. Plant signaling & behavior, 2011, 6(4): 570-574.
- Fu J, Liu H, Li Y, et al. Manipulating broad-spectrum disease resistance by suppressing pathogen-induced auxin accumulation in rice[J]. Plant physiology, 2011, 155(1): 589-602.
- Terol J, Domingo C, Talón M. The GH3 family in plants: genome wide analysis in rice and evolutionary history based on EST analysis[J]. Gene, 2006, 371(2): 279-290.
- Jain M, Kaur N, Tyagi A K, et al. The auxin-responsive GH3 gene family in rice (Oryza sativa)[J]. Functional & integrative genomics, 2006, 6(1): 36-46.