Maize origin.pptx

Maize evolution

1. “THE GENETICS OF MAIZE EVOLUTION” MARUTHI PRASAD B. P. PAMB-1066 Department of Genetics and Plant Breeding 1

2. INTRODUCTION Maize is an important cereal and staple food crop of the world. Chromosome number: 2n=2x=20 Genome size: 2.3 gigabase C 4 photosynthetic plant Photo-insensitive crop with high adaptability Vital source of proteins and calories to billions of people. A source of important vitamins and minerals to the human body. 2

3. 3 Taxonomy of Maize Kingdom Plantae (plants) Subkingdom Tracheobionta (vascular plants) Superdivision Spermatophyta (seed plants) Division Magnoliophyta (flowering plants) Class Liliopsida (monocotyledons) Subclass Commelinidae Order Cyperales Family Poaceae (grass family) Genus Zea Species Zea mays ssp. mays

4. UTILIZATION OF MAIZE IN THE WORLD AND IN INDIA Source: https://www.researchgate.net/profile/Shankar_Jat/publication/260094182/figure/fig12/AS:668222319767574@1536328024791/Current-utilization-pattern-of-maize-for-different-purposes-in-India-and-in-Global-Maize.jpg 4

5. Area (m ha) Production (m t) Productivity (t ha -1 ) Globally 193.7 1147.7 5.75 India 9.2 27.8 2.96 Karnataka 1.3 4.4 2.77 AREA, PRODUCTION AND PRODUCTIVITY OF MAIZE Source: FAOSTAT, 2020, https://iimr.icar.gov.in/ , Anon.,2016. Source: https://iimr.icar.gov.in/wp-content/uploads/2020/05/img15-1.jpg 5

6. Where does the corn comes from? 6

7. The term ‘maize’ is derived from the word ‘ mahiz ’ of Taino language of the Caribbean islands, which became ‘ maiz ’ in Spanish (Oxford dictionary 2015 ). Origin: Mexico and Central America Origin of Maize 7

8. Unlike most crops, maize does not have a morphologically similar wild progenitor. Particularly, maize has no wild relative having a cob-like pistillate inflorescence (ear). 10

9. 12 Tripsacum Tripsacum dactyloides Common name : Eastern gamagrass Chr. No.: x=18, 2n=36,72 It is a grassy type Teosinte Zea mays spp. parviglumis Common name: Balsas teosinte Chr. No.: x=10, 2n=20 Morphology is similar to maize but branchy type.

10. Theories of origin of maize 13 1. Tripartite hypothesis 2. Catastrophic sexual transmutation theory 3. Tripsacum - Zea diploperennis hypothesis 4. Teosinte hypothesis

11. 1.Tripartite Hypothesis Proposed by Mangelsdorf and Reeves (1938, 1939), and later elaborated by Mangelsdorf (1974). 14 Mangelsdorf and Reeves, 1938

12. 15 States that, “ Maize was domesticated from some unknown wild, now extinct maize plant that had structures similar to the ear of modern maize” . Mangelsdorf and Reeves, 1938 Tripsacum TEOSINTE MAIZE Unknown wild maize from South America (extinct or undiscovered)

13. The hypothesis comprised three parts; The progenitor of maize was a wild maize prototype from South America, which has become extinct or remained undiscovered. Teosinte is the offspring of a cross between maize and Tripsacum . Sections of Tripsacum chromosomes had contaminated maize germplasm. 16 Mangelsdorf and Reeves, 1938

14. 17 Counter arguments for tripartite hypothesis (teosinte is the intermediate between Tripsacum and corn) Corn and Tripsacum have never been known to cross naturally , in spite of the fact the they grow in close proximity over millions of acres. Man-made crosses can be accomplished only with special techniques. None of the 18 chromosomes of Tripsacum pair normally with any of the 10 chromosomes of corn. The man-made crosses of corn and Tripsacum are completely male sterile .

15. 18 2. Catastrophic sexual transmutation theory (CSTT) Iltis ( 1983 ) proposed that maize was originated due to a sudden sexual transmutation that condensed the branches of teosinte and placed them in the female expression area of the plant. Iltis , 1983

16. 19 It states that the ear of maize was derived from the central spike of the tassel of teosinte. According to Iltis , this has happened due to a phenomenon known as ‘ genetic assimilation ’. This resulted in substantial alterations in the nutrient distribution of the plant and led to drastic morphological changes. Morphogenetic and structural imbalance possibly had led to the transformation into primitive maize. During the late 1980s, teosinte hypothesis started gaining importance and the catastrophic sexual transmutation theory became less convincing. Iltis , 1983

17. 20 3 . Tripsacum - Zea diploperennis hypothesis Tripsacum - Z. diploperennis hypothesis can be considered as a modern version of the tripartite hypothesis and was given by Eubanks ( 1995 ). Eubanks, 1995

18. 21 Eubanks, 1995 GAMA GRASS ( Tripsacum sp.) TEOSINTE ( Zea mays sp.) MAIZE ( Zea mays subsp. mays ) The Recombination Hypothesis

19. 22 Eubanks, 1995

20. 23 Counter arguments for recombinantion hypothesis Tripsacum and Z. diploperennis can not be hybridized successfully. The chromosome number of both ‘ Tripsacorn ’ and ‘ Sundance ’ is 2n = 20 . These hybrids would be expected to have 28 or 46 chromosomes if Tripsacum (2n = 36 or 72) had indeed been one of the parents. Of the polymorphisms identified by RFLP data, ‘ Tripsacorn ’ and ‘Sundance’ shared four times as many bands with Z. diploperennis than with Tripsacum , indicating a much closer relationship with teosinte than with Tripsacum . Besides, 23% of the molecular markers surveyed were not found in either of the parents . Eubanks, 1995

21. 24 4.Teosinte hypothesis Proposed by George Beadle (1939) States that teosinte is the sole progenitor of maize. Beadle believed that missing ancestor is not needed to explain the origin. He could obtain completely fertile hybrids between maize and teosinte. Beadle, 1939

22. 25 Highlights Teosinte provided a useful food source and ancient people cultivated it. During the cultivation of teosinte, mutations that improved teosinte’s usefulness to humans arose and were selected by people. As few as five major mutations would be sufficient to convert teosinte into a primitive form of maize. Different mutations controlled different traits, viz ., one mutation would have converted the disarticulating ear-type of teosinte into the solid ear type of maize. Over the period of time, humans selected additional major mutations coupled with many minor ones. Beadle, 1939

23. 26 Teosinte was placed under the genus Euchlaena . Beadle studied cytology and genetics of corn-teosinte crosses . He confirmed the fertility of the cross and showed that the 10 chromosomes in the cell of teosinte were highly compatible with 10 chromosomes of corn. The chromosomes paired normally during the formation of sex cells in the crossed plants. He concluded that cytologically and genetically corn and Mexican teosinte could even be considered as same species. Beadle, 1980

24. 27 Teosinte plant architecture is branched, with multiple ears per plant. Maize architecture is apically dominant, with side branches tipped by female inflorescence (ears) Teosinte v/s Maize

25. 28 Teosinte v/s Maize (Hossain et al. , 2016) 1. Teosinte plants are branched and produce many ears 2. Terminal position of primary branch bears a tassel 3. The leaves along the lateral branches are fully formed and composed of leaf blade and sheath 1. Maize plants produce a single upright stem with one or few ears 2. Primary branch is modified into ears 3. Leaves of the lateral branch are modified into husks which cover the ear 4. Secondary lateral branches are extremely rare 4. Secondary lateral branch is modified into ears

26. 29 5. Ears are covered loosely by a single or few husks 6. Each ear possesses only two kernel rows (distichous) 5. Ears are covered tightly by many husks 6.Each ear possesses about 8–22 kernel rows ( polystichous ) 7. Ear bear about 250–500 kernels 8. Each kernel is sealed tightly in a stony casing or fruit case 8. Each kernel is naked and not covered by any fruit case Teosinte v/s Maize 7. Ear possesses about 10–12 kernels (Hossain et al. , 2016)

27. 30 9. During development, out of two spikelets one is aborted, hence each fruit case holds a single-spikelet 10. At maturity, fruit case having the kernel shatter and become the dispersal units 9. Maize evolution involved the de-repression of the second spikelet primordium, hence there are two mature spikelets 10. At maturity, kernels do not shatter, and remain attached with ears 11. Seeds of maize do not possess dormancy Teosinte v/s Maize 11. Majority of teosintes possess varying degree of seed dormancy (Hossain et al. , 2016)

28. 33 https://i.pinimg.com/originals/b0/43/94/b04394965852d49c56d5f935e635d781.jpg

29. 39 Zea mays ssp. parviglumis

30. 40 Classification of genus Zea (include wild taxa, known as teosinte and domesticated corn) Phylogeny of the genus Zea Buckler and Stevens, 2006

31. 45 In modern form of teosinte hypothesis , Z. mays ssp. parviglumis (wild Mexican grass teosinte) has been pinpointed as the likely progenitor of maize. Further, maize arose through large changes in parviglumis – through artificial selection for specific traits. Most maize geneticists and evolutionists have now accepted that maize is a domesticated derivative of parviglumis . Beadle, 1980

32. 46 Studies on chromosome number and morphology Most Zea species and subspecies, including maize, have 10 chromosomes with the sole exception of Z. perennis , which has 20—clearly an example of a complete, duplicated set of chromosomes . On the other hand most Tripsacum species have either 18 or 32 chromosomes. Study of chromosome morphology among teosinte plants, Focusing on chromosomal knobs, revealed that certain grasses such as Tripsacum and several Zea species had terminal knobs only, whereas others, including three subspecies of Zea mays , displayed interstitial knobs. (Kato T. A., 1984; McClintock et al., 1981) Evidences supporting teosinte hypothesis

33. 47 2. Iso- enzymne studies: Zea can be divided into 2 major groups: Sect. luxuriants , including Z. perennis , Z. diploperenneis , and Z. luxurians . Sect. Zea , including Z. mays subsp. mays , subsp. parviglumis , and subsp. Mexicana. Zea mays var. huehuetenangenesis is iso-enzymatically distinct from both sections, but show its closest relationship to Z. mays var. parviglumis of sect. Zea . Population of Z. mays subsp. mexicana and var. parviglumis grade iso-enzymatically from one into other without any clear break, but without any overlap either. Doebley et al ., 1984

34. 48 Five population of Z. mays subsp mays are all iso-enzymatically very similar to Zea mays var parviglumis . The iso-enzyme data are consistent with the theory that Mexican annual teosinte is the ancestor of maize. The levels of variation within and among population of Zea taxa varies considerably. Zea taxa seems to have more variation than most other plant species for which iso-enzyme data are available Doebley et al ., 1984

35. Methods To study the meiotic behaviour of the Zea perennis Zea mays ssp Analyzing meiotic configurations in the hybrid - genomic source of each chromosome GISH and FISH – To established the genomic affinities between the parental species Materials Plant material Parents - Zea mays ssp. mays (race Amarillo Chico) Zea perennis F 1 Hybrid- Zea mays ssp. mays x Zea perennis

36. Cytological analysis Panicles from Zea mays ssp. mays, Zea perennis and their F1 hybrids were fixed in 3:1 (absolute alcohol:acetic acid) solution The pairing configurations were determined at diakinesis-metaphase I GISH and FISH Genomic DNA probes were isolated from adult leaves of Zea mays ssp. mays and Zea perennis The pTa 71 plasmid, containing the 18S-5.8S-25S ribosomal sequences from Triticum aestivum (Gerlach & Bedbrook 1979), was used as a probe

37. Results Meiotic behaviour Zea mays ssp. mays (2n = 20, genomic formula AmAmBmBm ) shows regular meiosis, forming 10 bivalents (II) in metaphase I

38. Zea perennis (2n = 40, ApApA¶pA¶p Bp1Bp1Bp2Bp2) is an amphioctoploid showing a IV (tetravalent) range from 2 to 6 The most frequent configuration being 5 IV + 10 II

39. The hybrid between Zea perennis and Zea mays ssp. mays (2n = 30, ApA¶pAmBmBp1Bp2) Five trivalents (III) + five bivalents (II) + five univalents (I) as the most frequent configuration The trivalents have the Frying pan shape and the bivalents are homomorphic

40. The association of homologous or homoeologous chromosomes during meiosis reveals the relative affinities between the parental genomes of the hybrids and polyploid species. These meiotic configurations detect chromosomal rearrangements that may act as reproductive isolation mechanisms. They did this type of analysis on Zea species , and on artificial hybrids between species with equal and different ploidy levels, we could deduce their polyploid nature and the genomic formulae of all species ( Poggio et al. 2005). Accordingly, two different genomes were postulated to occur in these cryptic polyploids, each with x = 5 chromosomes , which were arbitrarily named FA_ and FB_. The hypothetical formula proposed for 2n = 20 species was AxAxBxBx , and for Zea perennis ( 2n = 40 ) ApApA¶pA¶pBp1Bp1Bp2Bp2 (Naranjo et al. 1994).

41. Meiotic analysis of the hybrid Zea perennis Zea mays ssp. mays , whose putative genomic formulae is ApA¶p Am Bp1 Bp2Bm Where ApA¶p & Bp1 Bp2 –From Zea perennis Am & Bm – From Zea mays ssp. Mays This hybrid formed 5 III + 5 II + 5 I, as the most frequent configuration at metaphase I. It would not be possible to recognize reliably the parental source of the chromosomes involved in each meiotic configuration (i.e. III, II, I) using classical plant chromosome staining methods

42. In-situ hybridization experiments In-situ hybridization experiments targeted mitotic chromatin of Zea mays ssp. mays and Zea perennis Total DNA of Zea perennis was hybridized as a probe onto Zea mays ssp . mays chromosomes The fluorescence signal was absent from at least two pairs of metacentric chromosomes and from all heterochromatic (DAPI-positive) knobs of maize A dispersed signal was observed in the rest of the chromosomes.

43. Labelled maize DNA was hybridized to maize chromosomes competitively with unlabelled total DNA from Zea perennis. They observed strong differential fluorescence on all DAPI-positive knobs in maize On the other hand, total labelled DNA of Zea mays ssp. mays hybridized to Zea perennis chromosomes yielded a hybridization signal uniformly dispersed across the whole complement

44. GISH was carried out on meiotic chromatin of the hybrid Zea perennis Zea mays ssp. mays (2n = 30) In this case chromosomes were blocked with unlabelled Zea perennis genomic DNA and probed with labelled total genomic DNA from Zea mays ssp . Mays This resulted in a fluorescence signal on all the univalents , but on none of the bivalents. Further indicating their homomorphic composition Trivalents , where observed, showed a strong fluorescence signal on the F handle_ of the Ffrying pan_ configurations

45. Inference: Trivalents are formed by autosyndetic pairing (pairing of chromosomes coming from the same parental gametes) of genomes ApA¶p from Zea perennis and by allosyndetic pairing (pairing of chromosomes coming from different parental gametes) of genomes Am from maize Bivalents result from autosyndetic pairing of genomes Bp1 and Bp2 from Zea perennis Univalents correspond to genome Bm of Zea mays ssp. mays . Similar results were obtained by Poggio et al. (2000) when analysing the hybrid Zea luxurians Zea perennis Conclusion: conclude that the formation of bivalents and univalents is not random, and that the FA_ genome of 2n = 20 species is more homologous to the FA_ genomes of Zea perennis than to its own FB_ genome, strongly suggesting a hybrid origin for the genus, with a common progenitor for both taxa These results reinforce the hypothesis of the amphiploid origin of Zea perennis, and would indicate that the chromosomes with divergent repetitive sequences both in maize and Zea luxurians could be remnants of a relict parental genome not shared with Zea perennis

46. FISH experiments Carried out using the pTa71 probe (45S rDNA from Triticum aestivum ), which labels the nucleolar organizer regions. The pTa71 probe was hybridized to Zea mays ssp. mays and Zea perennis mitotic cells, two and four signals were detected respectively.

47. The rDNA probe was hybridized to meiotic cells of the Zea perennis Zea mays ssp. mays hybrid Three fluorescence signals were observed on a single trivalent (80% of 50 cells analysed ) Two signals on a bivalent plus one on a univalent (20% out of 50 cells analysed )