PhD Oral Exam - Nilesh Gawande, Biology

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Global food security has been an important issue to meet the food requirement of the increasing population. Most of the food comes from the cereals such as rice, wheat and barley. The common bread wheat, Triticum aestivum belong to the tribe Triticeae and serve as the second staple food choice for many globally. The minimization of losses in the crop yield caused by the biotic and abiotic will be beneficial and another way to increase the crop production in the crops including wheat. The second generation sequencing is helpful in determining the members of gene families that respond to particular stress conditions. Several gene families in T. aestivum that respond to abiotic stress conditions have been characterised. G protein gene families has been long known to be involved in the regulation of plant growth and development under control and stress conditions and these gene family members are also found to interact to other proteins hence playing regulatory roles. Here we characterised the G protein gene families in the T. aestivum. Calcium binding proteins, Caleosins are one of such proteins that are known to interact with G protein α subunit and regulate stress responses through abscisic acid signalling. T. aestivum Gα is known to interact physically with its Caleosin 3. It will be interesting to know if the caleosins in Brachypodium also interact with its Gα subunit. It is difficult to determine the effect of mutation in the wheat due to its allohexaploid nature; therefore, a diploid Brachypodium distachyon can serve as a best model plant for cereals to determine the effect of the mutation. Here we did the functional characterization of the two caleosin mutants in B. distachyon for regulation of root growth.

The first study (Chapter 2) of this thesis characterises G protein gene families in T. aestivum. Two of the Gγ’ were validated through in vivo protein-protein interaction by bimolecular fluorescence complementation. The gene expression analysis for heterotrimeric G protein gene family members in T. aestivum using RNA-Seq and microarray showed that these members responded to stress conditions such as drought, heat cold stress and in response to Fusarium graminearum inoculation. Gγ’s showed the diverse gene expression pattern under different stress conditions. This study will create a rationale to elucidate the possible role of G protein gene family members in wheat under these stress conditions, which can be further investigated through mutant analysis.

The second study (Chapter 3) of this thesis report the physical interaction of B. distachyon G protein subunit Gα with its CALEOSIN 7 (Bd-CLO7) and the role of CLO7 in regulation of root growth. We investigated the effect of Brachypodium CLO7 mutation on the regulation of primary, coleoptile node and lateral root growth under normal growth conditions and, ABA and osmotic stress. Brachypodium CLO7 regulates the lateral root growth under osmotic stress condition through ABA independent signalling.
The third study (Chapter 4) of this thesis determines the physical interaction of Brachypodium CALEOSIN 3 (Bd-CLO3) and its N and C terminal truncations with Bd-Gα. We investigated the role of Brachypodium Caleosin 3 in the regulation of primary, coleoptile node and lateral root growth under ABA and osmotic stress by mutant analysis. Bd-CLO3 has been found to affect the primary root growth under ABA and osmotic stress and negatively regulate coleoptile node root growth under non stress and osmotic stress conditions. Brachypodium CLO3 negatively regulate of the lateral root growth through ABA signalling, whereas under osmotic stress it affects lateral root growth through both ABA dependent and independent pathways.