Rishikesh Bhalerao standing in a growth room at one of UPSC's greenhouses with aspen trees in front and behind him Photo: Andreas PalménOverarching goal of my research group is to understand the mechanistic basis of growth adaptation in plants. We are using two experimental models to study growth adaptation. In the first project, we are using annual growth cycles in perennial plants as a model to understand how plants use environmental cues such as photoperiod and temperature to control the timing of seasonal growth transitions in hybrid aspen. In second project, we are using apical hook (a structure that forms by bending of hypocotyl as seedling emerges from soil) as a model to understand how mechanical cues regulate differential growth to facilitate tissue bending in Arabidopsis thaliana. We use genetical, cell biological and biophysical approaches combined with mathematical modelling in our work.

Project 1: Seasonal control of annual growth cycles

Perennial plants need to undergo growth cessation and establish dormancy prior to the onset of winter, in order to survive low temperatures. These plants anticipate the approach of winter by sensing the reduction in day length. Reduction in day length (short day signal) induces growth cessation that is apparent in the form of bud formation at the apex and eventually the establishment of dormancy. Once dormancy is established, prolonged exposure to chilling temperatures is essential for release from dormancy. Once release from dormancy has occurred, warm temperatures can re-initiate new growth. In this project our focus is on identifying the molecular basis of how short-day signal induces growth cessation and dormancy and how temperature cues induce dormancy release and activate growth in hybrid aspen. Our key findings so far can be found in recent publications (1-9).

Project 2: Mechano-chemical control of tissue bending

Unlike animal cells, plant cells do not contract or migrate. As a result, differential cell elongation is a key mechanism used for tissue bending in plant morphogenesis. We are interested in elucidating the mechanistic basis of how mechanical cues regulate differential growth and how this facilitates tissue bending in plants. To address this, we are using the apical hook development as a model. Apical hook is a structure formed by the bending of the hypocotyl during early seedling establishment as seedling emerges through the soil. We have discovered that hypocotyl bends in response to mechanical cues when seeds germinate inside the soil as hypocotyl pushes through the soil. In contrast with animals, plant cells are enclosed within a rigid cell wall and therefore remodeling of cell wall is expected to play a critical role in differential growth. We are using genetical, cell biological and biophysical approaches to investigate the control of differential cell elongation during apical hook development. These studies (10-13) have so far uncovered an interplay between plant hormones such auxin and ethylene, primary cell wall components (such pectin, xyloglucans and cellulose) and cytoskeleton in regulation of hypocotyl bending during apical hook development in Arabidopsis.

Key Publications

  1. Maurya J., Misckolzi P., Mishra S., Singh R and Bhalerao RP (2020) A genetic framework for regulation and seasonal adaptation of shoot architecture in hybrid aspen. PNAS 117(21): 11523-11530
  2. Maurya JP., Singh R., Misckolczi P., Prasad AN., Jonsson K., Wu F and Bhalerao RP (2020) Branching regulator BRC1 mediates photoperiodic control of seasonal growth in hybrid aspen. Current Biology 30: 122-126
  3. Misckolczi P., Singh RK., Tylewicz S., Azeez A., Maurya JP., Tarkowska D., Novak O., Jonsson K and Bhalerao RP (2019) Long-range mobile signals mediate seasonal control of shoot growth. PNAS 116: 10852-10857
  4. Singh R., Misckolczi P., Maurya JP and Bhalerao RP (2019) A tree ortholog SHORT VEGETATIVE PHASE floral repressor mediates photoperiodic control of bud dormancy. Current Biology 29: 128-133
  5. Singh R., Misckolczi P., Maurya JP., Azeez A., Tylewicz S., Busov V and Bhalerao RP (2018) A genetic network mediating the control of bud break in hybrid aspen. Nature Communications 9: 4173
  6. Tylewicz S., Petterle A., Martilla S., Misckolzi P., Singh R., Immanen J., Mähler N., Hvidsten T., Eklund D., Bowman J., Helariutta Y and Bhalerao RP ( 2018) Photoperiodic control of seasonal growth is mediated by ABA acting on cell-cell communication. Science 360: 212-215
  7. Singh R., Svystun T., AlDahmash B., Jönsson AM and Bhalerao R (2017) Photoperiodic and temperature mediated control of phenology in trees-a molecular perspective. New Phytologist 213:511-524
  8. Tylewicz S., Tsuji H., Miskolczi P., Petterle A., Azeez A., Jonsson K., Shimamoto K and Bhalerao RP (2015) Dual role of tree florigen activation complex component FD in photoperiodic growth control and adaptive response pathways. PNAS 112: 3140-3145
  9. Azeez A., Miskcolzi P., Tylewicz S and Bhalerao RP (2014) A tree ortholog of APETALA1 mediates photoperiodic control of seasonal growth. Current Biology 24: 717-724
  10. Boutté Y., Jönsson K., McFarlane HE., Johnson E., Gendre D., Swarup R., Friml J., Samuels L., Robert S and Bhalerao RP (2013) ECHIDNA-mediated post-golgi Trafficking of Auxin Carriers for Differential Cell Elongation in Arabidopsis. PNAS 110:16259-16264.
  11. Jonsson K., Gendre D., Singh R., Boutte Y and Bhalerao R (2017) Ethylene regulation of differential growth is mediated by BIG ARF-GEF dependent post-Golgi secretory trafficking in Arabidopsis. Plant Cell 29: 1039-1052
  12. Aryal B., Jonsson K., Baral A., Sancho-Andrés G., Routier-Kierzkowska., Kierzkowski D and Bhalerao RP (2020) Interplay between cell wall and auxin mediates the control of differential cell elongation during apical hook development. Current Biology 30(9):1733-1739.e3
  13. Baral A., Morris E., Aryal B., Jonsson.,Verger S., Xu T., Bennett M., Hamant O and Bhalerao RP (2020) External mechanical cues reveal core molecular pathway behind tissue bending in plants. bioRxiv 2020.03.05.978296

Our work is funded by generous support from:

Logo of the Swedish Research CouncilLogo of the Knut and Alice Wallenberg FoundationLogo of the Human Frontier Science Program (HFSP)Logo of Kempestiftelserna -  the Kempe FoundationsLogo of Marie Skłodowska-Curie ActionsLogo of Formas, a Swedish Research Council for Sustainable DevelopmentLogo of the Swedish Foundation for Strategic Research