Investigating Non-Photochemical Quenching

Cailin Smith Author

07/27/2020 Added

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Poster presentation about research done during summer 2020 about non-photochemical quenching.

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[00:00:00.706]Hello, my name is Cailin Smith
[00:00:02.446]and this presentation is about
[00:00:04.103]investigating non-photochemical quenching.
[00:00:06.860]I will be presenting on 3 distinct
[00:00:08.688]projects, each at a different level of
[00:00:10.561]completion, yet all relating to the
[00:00:12.382]applications of improving non-photochemical
[00:00:14.631]quenching and photosynthesis.
[00:00:17.121]First, I will introduce the chloroplast
[00:00:18.882]project. Non-photochemical quenching,
[00:00:21.156]which I will now refer to as NPQ,
[00:00:23.107]is the mechanism plants use to protect
[00:00:25.206]themselves from high light intensity
[00:00:26.921]by redirecting solar energy into heat.
[00:00:29.673]The efficiency of NPQ is dependent upon
[00:00:32.000]the size and shape of the chloroplast,
[00:00:33.787]which is determined by the rate of
[00:00:35.324]plastid division.
[00:00:37.848]This figure depicts the proteins
[00:00:39.477]involved in the plastid ring division
[00:00:41.272]complex of land plants. I want to
[00:00:43.287]draw special attention to the proteins
[00:00:44.866]FtsZ and PDV1 and 2.
[00:00:49.628]In transgenic plants, perturbation of the
[00:00:52.017]levels of FtsZ and PDV results in
[00:00:54.680]plastid division defects and abnormal
[00:00:57.405]chloroplast size. For the chloroplast
[00:00:59.557]project, Arabidopsis FtsZ and S. lycopersicum
[00:01:03.012]PDV were overexpressed in transgenic
[00:01:05.570]N. tabacum in order to investigate
[00:01:07.225]how the manipulation of chloroplast size
[00:01:09.281]may improve NPQ and therefore photosynthesis.
[00:01:13.774]Cells from 4 transgenic lines of N. tabacum
[00:01:15.889]and corresponding wild types were all
[00:01:17.943]imaged using the same microscope. However,
[00:01:20.325]the chloroplasts within the images had to
[00:01:22.276]be analyzed using 2 different approaches,
[00:01:24.198]as summarized in table 1.
[00:01:26.585]Because the FtsZ mutants resulted in such
[00:01:28.880]large chloroplasts, those had to be
[00:01:30.939]measured by hand in a program called
[00:01:32.718]ImageJ. The PDV mutants and the wild type
[00:01:35.515]were all measured automatically using
[00:01:37.664]Weka Trainable Segmentation software.
[00:01:40.981]After analysis, the following results
[00:01:42.830]were elucidated.
[00:01:44.718]The overexpression of FtsZ resulted in
[00:01:47.143]much larger chloroplasts. Compared to the
[00:01:49.425]longest dimension in wild type, which is
[00:01:51.252]about 8, the longest dimension of the
[00:01:54.281]FtsZ mutants was about 2.6 times longer.
[00:01:58.207]The ratio of shortest-to-longest dimension
[00:02:00.480]is an indication of circularity, in which
[00:02:02.660]1 is a perfect circle. As for the PDV
[00:02:05.380]mutants, it was found that both PDV1 and
[00:02:08.317]PDV2 result in smaller chloroplasts, while
[00:02:11.570]the cross between PDV1 by PDV2 had the
[00:02:14.397]strongest effect on chloroplast size
[00:02:16.953]all around.
[00:02:20.152]Now, I will shift to the gene mapping
[00:02:21.831]project by explaining the results
[00:02:23.684]of a genome wide association study,
[00:02:25.347]or GWAS.
[00:02:27.700]This table summarizes the results from
[00:02:29.461]two GWASs. Here, a significant association
[00:02:32.389]between single nucleotide polymorphisms,
[00:02:34.851]or SNPs, and NPQ kinetics were detected
[00:02:37.783]in both Zea mays, which was grown in
[00:02:39.647]nitrogen deficient soil and in controlled
[00:02:41.426]soil, and in Sorghum bicolor, which was
[00:02:44.003]grown in controlled soil.
[00:02:46.552]A SNP is a genetic marker, while the
[00:02:48.685]frequency indicates the minor allele
[00:02:50.401]frequency of that SNP in the population.
[00:02:53.332]In maize, the 2 candidate genes that
[00:02:55.344]stuck out from the GWAS are
[00:02:56.831]glutaredoxin, or GRXS1, and
[00:02:59.126]5-phosphomevalonate kinase, or PMK.
[00:03:03.105]In sorghum, the 2 candidates are the
[00:03:05.075]cofactor of complex C, or CCB4, and
[00:03:08.439]argonaute 101.
[00:03:11.140]I will now discuss the roles of the
[00:03:12.800]proteins that are the products of the
[00:03:14.310]candidate genes from the GWAS.
[00:03:17.499]GRXS1 is a CC-type glutaredoxin, or GRX,
[00:03:21.536]and is specifically responsive to plant
[00:03:23.560]nitrate status. It acts as a negative
[00:03:25.895]regulator of vertical root growth
[00:03:27.588]in response to nitrogen, as seen here.
[00:03:31.534]PMK is an enzyme of the mevalonate
[00:03:33.479]pathway, which produces isoprenoids.
[00:03:35.969]Note that xanthophyll and chlorophyll
[00:03:37.757]are both isoprenoids, and are especially
[00:03:39.786]important to NPQ and photosynthesis.
[00:03:42.861]Another isoprenoid, cytokinin, is a plant
[00:03:45.788]hormone involved in cell signaling.
[00:03:49.384]CCB4 is a subunit of the cytochrome b6f
[00:03:52.401]complex, which is a major step in the
[00:03:54.573]electron transport chain in chloroplasts.
[00:03:57.327]This figure depicts a simplified role of
[00:03:59.367]cytochrome b6f in the light reaction
[00:04:01.453]of photosynthesis. Studies have found
[00:04:03.810]that disrupting the CCB4 gene leads to
[00:04:06.436]photosynthesis impairment.
[00:04:09.208]Argonaute101 is the central protein
[00:04:11.822]of the RNA-induced silencing complex,
[00:04:14.232]and is characterized by its
[00:04:15.671]catalytic PIWI domain.
[00:04:19.080]Finally, I am brought to the phenotyping
[00:04:20.948]project, the purpose of which is to
[00:04:22.746]investigate how soil nitrogen levels
[00:04:24.615]affect the kinetics of NPQ in a diverse
[00:04:27.197]set of maize genotypes.
[00:04:29.389]So far in this project, leaf samples from
[00:04:31.759]1,680 individual plants have been collected.
[00:04:35.532]The fluorescence of each sample was
[00:04:37.028]recorded during a 10-minute period of
[00:04:38.862]high light in order to measure the
[00:04:40.458]kinetics of NPQ induction,
[00:04:42.179]followed by a 10-minute period of
[00:04:43.901]darkness in order to measure the kinetics
[00:04:45.739]of NPQ relaxation, the results of which
[00:04:48.511]can be visualized by this example graph
[00:04:50.616]of NPQ kinetics.
[00:04:53.724]Using this method, approximately 1,160,000
[00:04:57.566]individual data points have been obtained.
[00:04:59.841]The next step of this project will be
[00:05:01.454]to analyze the rates of NPQ across
[00:05:03.572]different levels of soil nitrogen in order
[00:05:05.822]to confirm the results of the GWAS
[00:05:07.476]from the gene mapping project.
[00:05:09.645]I would like to acknowledge that this work
[00:05:11.317]is supported by the National Science
[00:05:12.708]Foundation, EPSCoR, and the University of
[00:05:15.316]Nebraska-Lincoln Center for Root and
[00:05:17.269]Rhizobiome Innovation.
[00:05:18.951]Thank you for your attention, and
[00:05:20.367]I will now be taking any questions.

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Investigating Non-Photochemical Quenching

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