ANNOUNCEMENTS
Rapeseed mustard is an important oilseed crop. India ranks third in global mustard oil production. However, realized potential of the crop is severely compromised owing to a variety of reasons including environmental stresses. The thesis entitled "Characterization of Key regulatory elements involved in fruit development and flowering time in Brassicas" demonstrates two distinct strategies for mitigation of yield losses in crop Brassicas. The first strategy provides a proof-of-concept for achieving earliness in flowering, an agronomic trait of interest in Brassicas. An early maturing crop promises effective evasion of abiotic and biotic stresses thus preventing losses in the field. The second strategy relates to design and generation of an artificial miRNA based gene silencing technology for down-regulation of genes at will. Asynchronous pod shattering in canola accounts for up to 50% of yield losses. This study provides pertinent molecular evidence supporting deployment of artificial miRNAs for controlling pod shattering in Brassicas.
For introgression of earliness in flowering, homologs of major effect gene, LEAFY (LFY) were characterized from Brassicas. LFY regulates flowering time and floral meristem identity. Sequence characterization of Brassica LFY homologs led to identification of at least two LFY homologs LFYa and LFYb. Analysis of differential expression of LFYa and LFYb indicated novel functions that have not been reported so far. Functional characterization of LFYa transcripts was undertaken in A. thaliana genetic background wherein flowering time was seen markedly reduced across all transgenics. Further, functional characterization of a Brassica LFYa transcript led to early flowering (20 days earlier) in Brassica transgenics (T1) relative to wild type.
For introducing pod shatter resistance, simultaneous silencing of SHATTERPROOF1 (SHP1) and SHATTERPROOF2 (SHP2) was proposed as these redundantly regulate valve margin formation in Brassicas enabling a seed dispersal process which unfortunately leads to substantial yield losses. BrassicaSHP1/SHP2 homologs were isolated to assess transcriptional diversity in complex genome of B. juncea. Two amiRNAs specific to SHP1 and SHP2 transcripts were designed and analyzed for their efficacy employing thermodynamic parameters. A series of transient expression analyses were undertaken to study amiRNA-transcript interaction that established potency of a single amiRNA in catalyzing efficient cleavage of all isolated SHP1/SHP2 targets. To conclude, this doctoral work demonstrates efficient implementation of gain-of-function and amiRNA technology as two distinct approaches for mitigating yield losses in crop Brassicas
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