As germination occurs, a seedling of a plant must undergo many developmental changes. Light exposure can induce inhibition of hypocotyl elongation, opening and greening of cotyledons and the extension of roots. On the other hand, Plant hormones also play a role in seedling growth, e.g., brassinosteroids(BR) inhibit cotyledon open (this protects the shoot apical meristem of the seedling when it is in the soil). We can therefore see that light and brassinosteroids work in contrasting ways to negate the effect of each other. However the molecular regulation of this interplay is still not well understood.

Ms. Nevedha Ravindran is a PhD student at the Plant Cell and Developmental Biology Lab at IISER Bhopal. She joined the lab in August 2015 after completing a B.Tech in Agricultural Biotechnology. Her recent study ‘B-box protein BBX32 integrates light and brassinosteroid signals to inhibit cotyledon opening’ deals with the identification of one of the elements of the molecular interplay between light and brassinosteroids. To further learn about the research behind this paper, the Chrysalis team got in contact with Ms. Nevedha.

She and her fellow scientists discovered the role of a B-Box protein BBX32 in regulating light and BR signaling. BBX proteins are those which have zinc finger transcription factors, i.e., transcription factors which have a zinc finger-binding domain and a transcription-factor effector-domain that has a modulatory effect (or regulates) in the vicinity of the sequence to which the protein domain binds). BBX32 has been previously reported to regulate flowering, hypocotyl elongation and root growth in Arabidopsis and to enhance the seed yield in soybean. Ms. Nevedha’s group found that BBX32 negatively regulates light signaling and promotes BR signaling, thereby having an overall effect of inhibiting cotyledon opening. Cotyledon opening inhibition is important for seedlings in dark conditions and consistent with this, it was found that BBX32 is highly expressed in cotyledons of seedlings grown in dark as well as the early stages of those grown in the light.

Her research group’s matter of interest is the light mediated molecular regulations of plant development. This includes BBX proteins which are zinc finger transcription factors (transcription factors which have a zinc finger-binding domain and a transcription-factor effector-domain that has a modulatory effect in the vicinity of the sequence to which the protein domain binds) There are 32 members in the BBX family and each PhD student in the group deals with the different developmental aspects regulated by the different BBX genes.

Ms. Nevedha wanted to understand how BBX proteins help in regulating the

cotyledon closure/opening when a seedling is exposed to light. Various BBX proteins were tested for their tissue specific expression and it was observed that BBX32 expressed specifically in cotyledons.This lasts for a maximum of 1-3 days after seed germination and

slowly starts diminishing upon seedling development. This peculiar expression pattern is what led her to choose this specific gene to study.

Not surprisingly, every project has its obstacles. A seedling that is grown in darkness shows skotomorphogenic development (highly elongated hypocotyl, closed and unexpanded cotyledons, short roots) and one grown in light shows photomorphogenic development (exhibit short

hypocotyl, opened and expanded cotyledons and longer roots). In dark, the hypocotyl cells elongate and cotyledon cell does not grow whereas in light, the hypocotyl cell size reduces and cotyledon cells elongate. Nowthe downstream genes that regulate cell elongation hypocotyls and cotyledons happen to be common. Therefore, if the downstream molecular regulation responsible for cotyledon cell growth is to be studied, it needs to be studied as a tissue specific mechanism i.e, the cotyledons and hypocotyl have to be isolated separately in dark or light. Currently there aren’t many in vitro techniques that can be used here to find out the tissue specific mechanisms as they have contrasting characteristics in the two organs. This makes the separation of cotyledons and hypocotyls from different genotypes in dark laborious and challenging.

Ms. Nevedha’s recent work has implications in enhancing agricultural productivity by establishing an optimum seedling after germination. She concluded our conversation with how she and her team will be continuing to work on the BBX32 protein. In their cotyledon opening project, they found out how BBX32 acts to connect the hormone and light pathways to regulate cotyledon opening. During their experiments, they had gotten leads that BBX32 also acts in regulating UV stress and high light stress. They have begun conducting some initial experiments to show that BBX32 is essential to tolerate mechanical stress imposed by soil, which would be the future direction for the current study.