Genetic Mechanisms of Pre-Attachment Striga hermonthica (Del.) Benth., Resistance in Sorghum Revealed by Ribonucleic Acid Sequencing
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Date
2024-03
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Kenyatta University
Abstract
Striga hermonthica is an obligate root parasitic plant that has a significant negative
impact on the yield of major crops in sub-Saharan Africa, causing devastating yield
loss to already struggling economies. This parasite has purple flowers with tinny
dusty seeds of 0.2 to 0.5 mm that are easily dispersed. Within the soil, they can stay
dormant for up to a decade waiting for ideal conditions to align, to ensure successful
germination near a potential host. S. hermonthica seeds germination is a decision
mediated by endogenous hormones in response to different environmental cues, of
which the most important are different strigolactones which are found within a
complex blend of many secondary metabolites exuding from nearby plant roots.
Although S. hermonthica seeds depend on strigolactones to germinate, little is known
about how it produces or uses hormones that play important roles in the germination
of its seeds and how they react to differences in root exudate composites from
potential hosts as they germinate. This study presents a transcriptomics analysis of
how hormones regulate S. hermonthica seeds germination upon exposure to root
exudates from both susceptible and resistant sorghum genotypes, and a synthetic
Strigolactone GR24. The study investigated the expression patterns of genes
involved in the biosynthesis of major hormones during S. hermonthica seed
germination at different time points (6, 12, and 18 hours) upon germination induction
and used preconditioned but untreated seeds as control. Resulted transcripts entail
that Violaxanthin de-epoxidase (VDE) inhibits the ABA biosynthesis a hormone that
promotes seeds dormancy. The biosynthesis of Gibberellic acid (GA1 and GA4)
promotes seed germination and its biosynthesis was highly enriched at 18 hours in
seeds treated with SRN39 root exudates, suggesting that the pre-attachment
resistance associated with this genotype is due to delayed germination in contrast to
other resistant genotypes (IS27146 and IS 41724), ABA and Auxin were highly
upregulated in seed that showed the least germination metrics. Overall, GA and ABA
were the main hormones that controlled germination and GR24-treated seeds showed
a relatively different germination mechanism from what was observed in seeds
treated with sorghum root exudates. This study shows how S. hermonthica
germination program and rate varies according to different germination stimulants
from root exudates. Therefore, profiling of these root exudates is recommended.
Findings in this study are necessary for future Striga resistant sorghum breeding
programs.
Description
A Research Thesis Submitted in Partial Fulfilment of the Requirements for the Award of the Degree of Master of Science (Biotechnology) in the School of Pure and Applied Sciences of Kenyatta University. March, 2024