• Istituto di Biologia e Patologia Molecolari

Tel :+390649912200
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National Research Council
Istitute of Molecular Biology and Pathology CNR
Universit\u00e0 \Sapienza\ P.le A. Moro, 5 00185 Roma

The aim of  my research activity is to study the role and function of HD-Zip II transcription factors in shoot and root development in the model plant Arabidopsis thaliana. In particular my interest is mainly focused on two projects

Decipher the mechanism of action of HD-Zip II transcription factors
Transcriptional repression mediated by the EAR motif is emerging as one of the principal mechanisms of plant gene regulation. The discovery that the EAR motif interacts with TOPLESS (TPL) together with the demonstration of genetic interaction between TPL and histone deacetylase 19 (AtHDA19) support a model where EAR repressors, via recruitment of chromatin remodelling factors, facilitate epigenetic regulation of gene expression. Among the Arabidopsis transcription factors containing an EAR motif are the HD-Zip II proteins, involved in embryonic apical patterning, shoot apical meristem function and organ polarity. There are several evidence that the HD-Zip II proteins act as negative regulators of gene expression, and recent work demonstrated that HAT3/ATHB4 directly repress the expression of the ATHB2 gene. The presence of the EAR motif in these proteins led to hypothesize a repression mechanism acting via TPL. Consistent with this hypothesis, we have recently found that HAT3 and TPL physically interact. The aim of the project is to investigate the centrality of the HAT3/TPL complex to HAT3 function in shoot development using molecular and phenotipyc  approaches.

Role of HD-Zip II transcription factors in the control of columella stem cell maintenance in the Arabidopsis root 

Plants’ lifelong growth and organ formation are dependent on the activity of pluripotent stem cells. In the root apical meristem (RAM) of Arabidopsis, stem cells surround a small group of less active cells, the Quiescent Center (QC). The QC, together with its surrounding stem cells, forms the root stem cell niche. The regulation of columella stem cell (CSC) activity has been intensively studied and a key role of auxin and several transcription factors has been identified. However, more insights are needed to unravel the network of transcription factors controlling CSC activity. We found that ATHB2, ATHB4 and HAT3 HD-Zip II transcription factors, known to play a crucial role in apical embryo development, are required for RAM organization and CSC maintenance. The aim of the project is to  investigate how ATHB2, ATHB4 and HAT3 interact with known regulatory molecules involved in the control of CSC activity using genetic, molecular and phenotypic approaches.


1-Ciolfi A., Sessa G., Sassi M., Possenti M., Salvucci S., Carabelli M., Morelli G., Ruberti I. (2013). Dynamics of the Shade-Avoidance Response in Arabidopsis Plant Physiology 163 (1), 331-353.

2-Turchi L., Carabelli M., Ruzza V., Possenti M. Sassi M., Penalosa A., Sessa G., Salvi S., Forte V., Morelli G., Ruberti I. (2013). Arabidopsis HD-Zip II transcription factors control apical embryo development and meristem function Development 140 (10), 2118-2129.

3-Cifuentes-Esquivel N., Bou-Torrent J., Galstyan A., Gallemi M., Sessa G., Martret M.S., Roig-Villanova I., Ruberti I., Martinez-Garcia J.F. (2013). The bHLH proteins BEE and BIM positively modulate the shade avoidance syndrome in Arabidopsis seedlings Plant Journal 75 (6), 989-1002.

4-Ruberti I., Sessa G., Ciolfi A., Possenti M., Carabelli M., Morelli G., (2011) Plant adaptation to dynamically changing environment: The shade avoidance response. Biotechnol Adv. doi:10.1016/j.biotechadv.2011.08.014.

5-Ciarbelli AR., Ciolfi A., Salvucci S., Ruzza V., Possenti M., Carabelli M., Fruscalzo A., Sessa G., Morelli G., Ruberti I. (2008). The Arabidopsis homeodomain-leucine zipper II gene family: diversity and redundancy. Plant Mol Biol. 68, 465-78. 

6-Carabelli M, Possenti M, Sessa G, Ciolfi A, Sassi M, Morelli G, Ruberti I. (2007). Canopy shade causes a rapid and transient arrest in leaf development through auxin-induced cytokinin oxidase activity. Genes & Development, vol. 21; p. 1863-1868

7-Sessa G., Carabelli M., Sassi M., Ciolfi A., Possenti M., Mittempergher F., Becker J., Morelli G., Ruberti I. (2005). A dynamic balance between gene activation and repression regulates the shade avoidance response in Arabidopsis. Genes & Dev  19 (23),  2811-2815. 

8-Steindler C., Matteucci A., Sessa G., Weimar T., Ohgishi M., Aoyama T., Morelli G., Ruberti I. (1999). Shade avoidance responses are mediated by the ATHB-2 HD-Zip protein, a negative regulator of gene expression Development 126 (19),  4235-4245. 

9-Sessa G., Steindler C., Morelli G., Ruberti I. (1998). The Arabidopsis Athb-8, -9 and -14 genes are members of a small gene family coding for highly related HD-ZIP proteins. Plant Mol. Biol. 38  (4), 609-622. 

10-Sessa G., Morelli G., Ruberti I. (1997). DNA-binding specificity of the homeodomain-leucine zipper domain. J. Mol. Biol. 274 (3), 303-309. 

11-Baima S., Nobili F., Sessa G., Lucchetti S., Ruberti I., Morelli G. (1995). The expression of the Athb-8 homeobox gene is restricted to provascular cells in Arabidopsis thaliana. Development 121 (12), 4171-4182. 

12-Sessa G., Morelli G., Ruberti I. (1993). The Athb-1 and Athb-2 HD-Zip domains homodimerize forming complexes of different DNA binding specificities. EMBO J. 12 (9), 3507-3517. 

13-Ruberti I., Sessa G., Lucchetti S., Morelli G. (1991). A novel class of plant proteins containing a homeodomain with a closely linked leucine zipper motif. EMBO J. 10 (7), 1787-1791. 

Giovanna Sessa obtained the Degree in Biological Sciences in 1990 at the University of Rome Sapienza and then, in 1996, achieved her PhD in Genetics and Molecular Biology at the same university. 

In the periods 1991-1993 and 1997-1999 she performed research activity as a fellow of the National Research Council at the Nucleic Acids Research Centre. In the years 2000 and 2001 she continued her activity as a young researcher at the same institution.

Since January 2002, she has a permanent position as researcher of the National Research Council and works at the Institute of Molecular Biology and Pathology in Rome.



1991: “Fondazione Istituto Pasteur-Fondazione Cenci-Bolognetti” Award for best experimental thesis in the field of pasteurian disciplines.

1997: “Fondazione Istituto Pasteur-Fondazione Cenci-Bolognetti” Award for best PhD thesis in the field of pasteurian disciplines.