Plant Organ Primordia


The shoot apical meristem (SAM) in plants is composed of totipotent cells that generate the major plant organs including leaves and flowers. Within the SAM synthesis and movement of auxin creates a hormonal flux. In production of leaf primordia, the hormonal flux alters a series small ribonucleic acids (RNAs) that impact the expression of homeotic genes. This results in the generation of a WUSCHEL/CLAVATA feedback loop that generate niches that result in the placement of leaf primordia. This placement of leaf primordia generates the overall phyllotaxis and nodal architecture that defines the major plant body. In perennial plants, seasonal cues alter primordia development resulting in shifts between true leaves and bud scales creating the overwintering meristem. How the transition between bud scales and leaf primordia occurs in unclear.

Key Concepts

  • The initiation of leaf primordia at nodes is regulated by an auxin gradient within the SAM.
  • A series of homeotic genes are associated with both SAM formation and establishment of leaf primordia and leaf organ symmetry including Knotted1, WUSCHEL‐RELATED Homeobox 1 and CLAVAT‐type (CLV) homoeotic genes.
  • Small RNAs play a critical role in the developmental processes associated with the SAM development.
  • Auxin flux is directed by PIN1 transporter polarity controlled by MONOPTEROS.
  • Responses to seasonal variation alter leaf primordia development.

Keywords: auxin; shoot apical meristem; SAM; organ primordia; plant architecture; WUS/CLV; pathway; MONOPTEROS; PIN‐FORMED; perennial buds; Arabidopsis thaliana

Figure 1. Variable primordia pattern formations found in shoot apices. These patterns are genetically controlled and specific to species.
Figure 2. Factors that control auxin efflux within the SAM and leaf primordia. Developmental zones are shown in blue. Orange indicates the CLV‐WUS feedback loop. Red arrows indicate auxin efflux, which is controlled by PIN1 polarity (pink). Controlling the PIN1 polarity in P0 is MP shown in green. ARR, Arabidopsis response regulator; CLV1‐3, CLAVATA1‐3; CK, cytokinin; CZ, central zone; GA, gibberellin; MP, MONOPTEROS; OC, organizing center; P0‐P1, leaf primordial; PIN1, PIN‐FORMED1; PZ, peripheral zone; RZ, rib zone; WUS, WUSCHEL. Adapted from Wang and Li and Bhatia et al. .


Arnaud N and Pautot V (2014) Ring the BELL and tie the KNOX: roles for TALEs in gynoecium development. Frontiers in Plant Science 5. DOI: 10.3389/fpls.2014.00093.

Bhatia N, Bozorg B, Larsson A, et al. (2016) Auxin acts through MONOPTEROS to regulate plant cell polarity and pattern phyllotaxis. Current Biology 26 (23): 3202–3208. DOI: 10.1016/j.cub.2016.09.044.

Brumos J, Robles LM, Yun J, et al. (2018) Local auxin biosynthesis is a key regulator of plant development. Developmental Cell 47 (3): 306–318. DOI: 10.1016/j.devcel.2018.09.022.

Byrne ME, Groover A, Fontana J and Martienssen RA (2003) Phyllotactic pattern and stem cell fate are determined by the Arabidopsis homeobox gene BELLRINGER. Development 130: 3941–3950. DOI: 10.1242/dev.00620.

Conde D, Moreno‐Cortés A, Dervinis C, et al. (2017) Overexpression of DEMETER, a DNA demethylase, promotes early apical bud maturation in poplar. Plant, Cell & Environment 40 (11): 2806–2819. DOI: 10.1111/pce.13056.

D'Ario M, Griffiths‐Jones S and Kim M (2017) Small RNAs: big impact on plant development. Trends in Plant Science 22 (12): 1056–1068. DOI: 10.1016/j.tplants.2017.09.009.

Edwards EJ, Spriggs EL, Chatelet DS and Donoghue MJ (2016) Unpacking a century‐old mystery: winter buds and the latitudinal gradient in leaf form. American Journal of Botany 103 (6): 975–978. DOI: 10.3732/ajb.1600129.

Ghanashyam C and Jain M (2009) Role of auxin‐responsive genes in biotic stress responses. Plant Signaling & Behavior 4 (9): 846–848. DOI: 10.4161/psb.4.9.9376.

Gruel J, Landrein B, Tarr P, et al. (2016) An epidermis‐driven mechanism position and scales cell niches in plants. Science Advances 2 (1): e1500989. DOI: 10.1126/sciadv.1500989.

Ingvarsson PK, García MV, Hall D, Luquez V and Jansson S (2005) Clinal variation in phyB2, a candidate gene for day‐length‐induced growth cessation and bud set, across a latitudinal gradient in European Aspen (Populus tremula). Genetics 172 (3): 1845–1853. DOI: 10.1534/genetics.105.047522.

Jackson D, Veit B and Hake S (1994) Expression of maize KNOTTED1 related homeobox genes in the shoot apical meristem predicts patterns of morphogenesis in the vegetative shoot. Development 120: 405–413.

Kuhlemeier C (2017) Phyllotaxis. Current Biology 27 (17): R882–R887. DOI: 10.1016/j.cub.2017.05.069.

Li C and Zhang B (2016) MicroRNAs in control of plant development. Journal of Cellular Physiology 231 (2): 303–313. DOI: 10.1102/jcp.25125.

Li S‐B, Xie Z‐Z, Hu C‐G and Zhang J‐Z (2016) A review of auxin response factors (ARFs) in plants. Frontiers in Plant Science 7. DOI: 10.3389/fpls.2016.00047.

Liu S, Wu L, Qi H and Xu M (2019) LncRNA/circRNA–miRNA–mRNA networks regulate the development of root and shoot meristems of populus. Industrial Crops and Products 133: 333–347. DOI: 10.1016/j.indcrop.2019.03.048.

Marrs KA (1996) The functions and regulation of glutathione S‐transferases in plants. Annual Review of Plant Physiology and Plant Molecular Biology 47 (1): 127–158. DOI: 10.1146/annurev.arplant.47.1.127.

Opseth L, Holefors A, Rosnes AKR, Lee Y and Olsen JE (2016) FTL2 expression preceding bud set corresponds with timing of bud set in Norway spruce under different light quality treatments. Environmental and Experimental Botany 121: 121–131. DOI: 10.1016/j.envexpbot.2015.05.016.

Overvoorde PJ, Okushima Y, Alonso JM, et al. (2005) Functional genomic analysis of the AUXIN/INDOLE‐3‐ACETIC ACID gene family members in Arabidopsis thaliana. The Plant Cell 17 (12): 3282–3300. DOI: 10.1105/tpc.105.036723.

Peaucelle AN, Louvet RN, Johansen JN, et al. (2011) The transcription factor BELLRINGER modulates phyllotaxis by regulating the expression of a pectin methylesterase in Arabidopsis. Development 138 (21): 4733–4741. DOI: 10.1242/dev.072496.

Ren H and Gray WM (2015) SAUR proteins as effectors of hormonal and environmental signals in plant growth. Molecular Plant 8 (8): 1153–1164. DOI: 10.1016/j.molp.2015.05.003.

Rohde A, Prinsen E, Rycke RD, et al. (2002) PtABI3 impinges on the growth and differentiation of embryonic leaves during bud set in poplar. The Plant Cell 14 (8): 1885–1901. DOI: 10.1105/tpc.003186.

Sablowski R (2011) Plant stem cell niches: from signaling to execution. Current Opinion in Plant Biology 14 (1): 4–9.

Shi J, Dong J, Xue J, et al. (2017) Model for the role of auxin polar transport in patterning of the leaf adaxial‐abaxial axis. The Plant Journal 92 (3): 469–480. DOI: 10.1111/tpj.13670.

Somssich M, Je BI, Simon R and Jackson D (2016) CLAVATA‐WUSCHEL signaling in the shoot meristem. Development 143 (18): 3238–3248. DOI: 10.1242/dev.133645.

Van de Poel B and Van Der Straeten D (2014) 1‐Aminocyclopropane‐1‐carboxylic acid (ACC) in plants: more than just the precursor of ethylene! Frontiers in Plant Science 5: 640. DOI: 10.3389/fpls.2014.00640.

Wang Y and Li J (2008) Molecular basis of plant architecture. The Annual Review of Plant Biology 59: 253–279. DOI: 10.1146/annurev.arplant.59.032607.092902.

Wang Y and Jiao Y (2018) Auxin and above‐ground meristems. Journal of Experimental Botany 69 (2): 147–157. DOI: 10.1093/jxb/erx299.

Further Reading

Drea S (2010) Petals. In: eLS. John Wiley & Sons Ltd: Chichester. DOI: 10.1002/9780470015902.a0002065.pub2.

Egea‐Cortines M and Weiss J (2013) Control of plant organ size. In: eLS. John Wiley & Sons Ltd: Chichester. DOI: 10.1002/9780470015902.a0003363.pub2.

Lin Sang Y, Juan Cheng Z and Sheng Zhang X (2018) iPSCs: a comparison between animals and plants. Trends in Plant Science 23 (8): 660–666. DOI: 10.1016/j.tplants.2018.05.008.

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Campbell, Michael, and Adams, Rachael(Mar 2020) Plant Organ Primordia. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002055.pub3]