Understanding Stress Response Mechanisms of Zea Mays Seeds Under Nitrogen Deficiency

Eric Cobos Author

08/02/2021 Added

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A brief analysis of the metabolic reprogramming of maize seeds under nitrogen stress.

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[00:00:00.750]My name is Eric Cobos.
[00:00:01.920]I'm a mechanical engineering student from Purdue university in west Lafayette.
[00:00:05.190]And I've been conducting some research in Dr.
[00:00:07.170]Saha's lab at the university of Nebraska in Lincoln.
[00:00:10.110]Today we're investigating the stress response of Zea mays seeds under nitrogen
[00:00:13.830]deficient conditions.
[00:00:16.590]Since this is a virtual representation of our poster presentation,
[00:00:19.890]I've included the my poster in the slides for easy access.
[00:00:23.250]Here's the first part. This is the second part,
[00:00:30.720]and this is the third part
[00:00:35.390]to begin Zea mays,
[00:00:36.920]better known as maize or corn is one of the globally most important crops for
[00:00:40.640]both food supply and for fuel production.
[00:00:43.820]With climate change affecting the production of maize investigating plant
[00:00:46.880]mechanisms of growth and response to stressors will be fundamental to improving
[00:00:50.690]plant survival and crop yield. among the most significant stressors is nitrogen
[00:00:54.890]deficiency. This is because plants require nitrogen in large amounts.
[00:00:58.880]The kernel,
[00:00:59.480]which is also the fruit of maize is perhaps the most important organ for the
[00:01:02.330]survival of the species.
[00:01:03.980]Therefore analyzing the stress response mechanisms and metabolic reprogramming
[00:01:07.700]of the maize seed could help maximize crop survival and yield.
[00:01:14.000]To understand the plant response mechanisms on an aggregate scale plant, genome
[00:01:17.690]scale metabolic models are used to simulate and predict metabolic reaction
[00:01:21.290]fluxes through optimization methods,
[00:01:23.390]including flux balance analysis and flux variability analysis.
[00:01:27.050]A genome scale metabolic model is simply the network of reactions or a network
[00:01:31.220]of reactions that function to model the metabolism of the plant.
[00:01:35.480]In this case,
[00:01:36.170]maize. Flux balance analysis utilizes linear programming to determine the steady
[00:01:40.910]state reaction flux.
[00:01:42.200]While flux variability analysis generates the range of flux maximum and minimum
[00:01:47.000]for reactions while maintaining some of its solid state and ultimately allows
[00:01:50.630]for investigation under unideal conditions.
[00:01:53.180]Therefore seed specific genome scale metabolic model was developed and analyzed
[00:01:58.190]using flux balance analysis and a flux variability analysis under nitrogen
[00:02:02.510]deficiency.
[00:02:05.690]The ranges outputted from the flux variability analysis created at least six
[00:02:09.050]specific conditions. Four of which are plotted here.
[00:02:12.560]The first condition is that reaction R00573 has a complete overlap
[00:02:17.240]and shrunk flux is important to note that the perspective that is being taken is
[00:02:21.230]that we are going from, N plus, which is nitrogen abundant to N minus,
[00:02:24.980]which is nitrogen deficient.
[00:02:26.480]So the red lines represent the flux of the specific reaction under ideal
[00:02:29.750]conditions.
[00:02:30.500]While the blue line represents the flux of the reactions under unideal conditions,
[00:02:34.400]as you can see in the first case from ideal conditions to unideal conditions,
[00:02:38.030]the range shrinks, but it is also completely overlapped,
[00:02:40.910]hence complete overlap and shrunk flux. And in the next condition,
[00:02:45.740]we can see that there is overlap again. However,
[00:02:47.990]going from ideal red conditions to unideal blue conditions it
[00:02:52.730]widens therefore reaction,
[00:02:54.410]R00935 has complete overlap and widened flux.
[00:02:59.740]And this third.
[00:03:00.280]Example, we can see that there is no overlap. And again,
[00:03:02.890]going from ideal to unideal conditions, the flux of the reaction decreases
[00:03:09.280]this fourth example is a little different because of its incorporation with
[00:03:12.340]negatives. Negatives in the case of reactions symbolizes the direction of reversible
[00:03:16.570]reactions and this case,
[00:03:18.280]the size of the flux doesn't really matter just that there is no overlap and
[00:03:21.370]that the new sign is different.
[00:03:22.960]And this case we're going from negative in ideal conditions to positive in
[00:03:26.830]unideal conditions.
[00:03:28.750]Since
[00:03:30.880]Each reaction could be categorized under a specific pathway pie charts are made
[00:03:34.300]to show what was happening to the flux of the reactions that were part of that
[00:03:37.540]specific pathway. For example,
[00:03:39.520]if we take a look at glycolysis and gluconeogenesis, which is directly above me,
[00:03:43.360]we can see that 33% of the reactions in that pathway experienced complete
[00:03:46.780]overlap and shrunk flux. Another 33% experienced, no overlap,
[00:03:50.920]but a decrease in flux in the same direction.
[00:03:53.080]And the final 33% experiences complete overlap and widened flux. As an
[00:03:57.820]overarching view, red and blue,
[00:03:59.470]which both signify a decrease in flux are expected to compose a majority since
[00:04:04.000]nitrogen plays a significant role in most, if not all of the depicted pathways,
[00:04:08.470]what we are interested in investigating are the green slices.
[00:04:11.320]This is because they represent the flux that increases.
[00:04:14.380]These reactions will reveal metabolites important to the plant while under
[00:04:17.650]stress, because the study revolves around nitrogen starvation,
[00:04:22.210]I was interested in analyzing amino acid pathways,
[00:04:27.240]numerous amino acid pathways, widened in flux, despite nitrogen starvation.
[00:04:31.170]This is interesting since, amino groups (-NH2),
[00:04:34.080]are nitrogen containing and would intuitively decrease.
[00:04:37.110]And this is not entirely the case.
[00:04:38.880]Two examples for analysis include arginine metabolism,
[00:04:41.850]which in which the majority of reactions, widened in flux, and glycine serine,
[00:04:45.750]and threonine metabolism,
[00:04:46.950]in which the reactions are nearly perfectly split between widened and
[00:04:50.070]decrease. The reactions of the metabolic pathways of metabolic pathways of arginine
[00:04:55.020]metabolism that widened in flux include the reactions bulleted beneath the image.
[00:04:59.700]All of these reactions had the primary pathway of arginine biosynthesis.
[00:05:04.140]This is significant because arginine functions as a major storage of nitrogen.
[00:05:08.280]Thus, despite nitrogen starvation,
[00:05:10.350]the production of arginine increases. The reaction in the metabolic pathways of
[00:05:15.060]glycine serine and threonine metabolism that increased in flux
[00:05:18.570]included the ones that are also bulleted beneath that one.
[00:05:21.720]These reactions had pathways
[00:05:23.850]to threonine biosynthesis. Threonine
[00:05:26.580]is an important molecule for cell signaling,
[00:05:28.800]especially under stress, among other things.
[00:05:31.320]This is significant because similar to arginine, under nitrogen starvation
[00:05:34.890]threonine is produced and stockpiled.
[00:05:39.680]Another interesting investigation was what was occurring with glycolysis and
[00:05:42.830]gluconeogenesis, a pathway that was decreasing despite its primary function,
[00:05:47.060]being pyruvate production and glucose metabolism.
[00:05:50.240]With the knowledge that ATP utilized in glycolysis and gluconeogenesis comes from
[00:05:54.860]the oxidation of fatty acids. I chose to investigate the metabolism of fatty acids,
[00:05:59.510]fatty acids, and its associated variation, unsaturated fatty acids,
[00:06:04.400]starting with unsaturated fatty acid metabolism.
[00:06:07.010]The reactions that were found to increase in flux are listed or are listed
[00:06:10.460]and were associated with a pathway for both synthesizing unsaturated fatty
[00:06:14.090]acids, as well as metabolizing fatty acids.
[00:06:17.120]In addition for fatty acid metabolism,
[00:06:19.490]the reactions that increased in flux are also listed and were found to produce
[00:06:23.180]acetoacetyl-CoA in other words, acetyl-CoA ,
[00:06:27.470]which is an important molecule for the Citrate cycle.
[00:06:30.350]We can overlap these results and say,
[00:06:31.970]if there's an increase in production of acetylcholine or that the increase in
[00:06:35.810]production,
[00:06:36.320]of acetyl-CoA is therefore likely a contributing factor to the 40%
[00:06:40.400]increase in reaction flux within the Citrate cycle.
[00:06:46.590]In summary,
[00:06:47.220]what was found was that in the investigation of integral amino acids,
[00:06:50.910]including arginine metabolism,
[00:06:52.770]as well as glycine serine and threonine metabolism is that under
[00:06:56.940]nitrogen starvation, the production of certain amino acids increase,
[00:07:00.840]presumably because,
[00:07:02.130]or presumably in an effort to preserve nitrogen and stockpile important
[00:07:05.250]metabolites. In addition, through the investigation of the fatty acid metabolism.
[00:07:10.020]It revealed that despite significant reduction in reaction flux the
[00:07:14.400]role of metabolites produced shed light upon the pathways and their associated
[00:07:18.060]reactants that are anticipated to be the most significant for the survival of
[00:07:21.270]the plant under the specific conditions. This focus,
[00:07:25.740]or this study focused on nitrogen deficiency.
[00:07:28.140]Future studies could expand with stressors, including salinity and drought.
[00:07:32.040]Furthermore, in combination with the study of the maize seed,
[00:07:34.800]the ultimate goal is to compile a plant level genome scale metabolic model of maize.
[00:07:39.330]So that the effects of stressors of all organs,
[00:07:41.700]including the leaf stem and root working together could be studied.
[00:07:47.900]I would like to acknowledge the university of Nebraska's center for root and
[00:07:50.870]rhizobiome innovation,
[00:07:52.340]as well as IDEA EPSCoR Nebraska and the National Science Foundation,
[00:07:57.020]which funded this project on track one grant. Thank you.

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Understanding Stress Response Mechanisms of Zea Mays Seeds Under Nitrogen Deficiency

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