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'''Function''' [[Maize]] gene for first step in biosynthesis of [[DIMBOA|benzoxazin]], which aids in resistance to insect pests, pathogenic fungi and bacteria.

'''First report''' Hamilton 1964,<ref name=Hamilton64>{{cite journal|last=Hamilton|first=RH|title=A corn mutant deficient in 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one with an altered tolerance of atrazine|journal=Weeds|year=1964|volume=12|issue=1|pages=27–30|jstor=4040633|doi=10.2307/4040633}}</ref> as a mutant sensitive to the herbicide [[atrazine]], and lacking benzoxazinoids (less than 1% of non-mutant plants).

Molecular characterization reveals that the BX1 protein is a [[Sequence homology|homologue]] to the alpha-subunit of [[tryptophan synthase]]. The reference mutant [[allele]] has a deletion of about 900 bp, located at the 5'-terminus and comprising sequence upstream of the transcription start site and the first [[exon]]. Additional alleles are given by a ''Mu'' [[transposon]] insertion in the fourth exon (Frey et al. 1997<ref name=Frey97>{{cite journal|last=Frey|first=M |author2=Chomet, P |author3=Glawischnig, E |author4=Stettner, C |author5=Grün, S |author6=Winklmair, A |author7=Eisenreich, W |author8=Bacher, A |author9=Meeley, RB |author10=Briggs, SP |author11=Simcox, K |author12=Gierl, A|title=Analysis of a chemical plant defense mechanism in grasses.|journal=Science|date=Aug 1, 1997|volume=277|issue=5326|pages=696–9|pmid=9235894|doi=10.1126/science.277.5326.696}}</ref> ) and a [[Ac/Ds transposable controlling elements|''Ds'' transposon]] insertion in the maize inbred line W22 genetic background (Betsiashvili et al. 2014<ref name=":0">{{Cite journal|last1=Betsiashvili|first1=M.|last2=Ahern|first2=K. R.|last3=Jander|first3=G.|date=2015|title=Additive effects of two quantitative trait loci that confer Rhopalosiphum maidis (corn leaf aphid) resistance in maize inbred line Mo17|journal=Journal of Experimental Botany|language=en|volume=66|issue=2|pages=571–578|doi=10.1093/jxb/eru379|pmid=25249072|issn=0022-0957|pmc=4286405}}</ref>). [[Gene sequence]] diversity analysis has been performed for 281 inbred lines of maize, and the results suggest that bx1 is responsible for much of the natural variation in DIMBOA (a benzoxazinoid compound) synthesis (Butron et al. 2010).<ref name=Butron10>{{cite journal|last=Butrón|first=A|author2=Chen, YC |author3=Rottinghaus, GE |author4= McMullen, MD |title=Genetic variation at bx1 controls DIMBOA content in maize.|journal=Theoretical and Applied Genetics|date=Feb 2010|volume=120|issue=4|pages=721–34|pmid=19911162|doi=10.1007/s00122-009-1192-1|url=https://digital.csic.es/bitstream/10261/24875/1/Genetic%20Variation%20at%20bx1%20Controls%20DIMBOA%20Content%20in%20Maize.pdf|hdl=10261/24875|s2cid=33310126|hdl-access=free}}</ref> Genetic variation in benzoxazinoid content influences maize resistance to several insect pests (Meihls et al. 2013;<ref>{{Cite journal|last1=Meihls|first1=L. N.|last2=Kaur|first2=H.|last3=Jander|first3=G.|date=2012|title=Natural Variation in Maize Defense against Insect Herbivores|journal=Cold Spring Harbor Symposia on Quantitative Biology|language=en|volume=77|pages=269–283|doi=10.1101/sqb.2012.77.014662|pmid=23223408|issn=0091-7451|doi-access=free}}</ref> McMullen et al. 2009<ref>{{Citation|last1=McMullen|first1=Michael D.|title=Genetics and Biochemistry of Insect Resistance in Maize|date=2009|work=Handbook of Maize: Its Biology|pages=271–289|editor-last=Bennetzen|editor-first=Jeff L.|publisher=Springer New York|language=en|doi=10.1007/978-0-387-79418-1_14|isbn=9780387794174|last2=Frey|first2=Monika|last3=Degenhardt|first3=Jörg|editor2-last=Hake|editor2-first=Sarah C.}}</ref>).

== [[Genetic map|Map]] location ==
AB [[chromosome translocation]] analyses place on short arm of [[chromosome]] 4 (4S; Simcox and Weber 1985<ref name=Simcox85>{{cite journal|last=Simcox|first=K. D.|author2=Weber, D. F.|title=Location of the Benzoxazinless (bx) Locus in Maize by Monosomic and B-A Translocational Analyses1|journal=Crop Science|year=1985|volume=25|issue=5|pages=827|doi=10.2135/cropsci1985.0011183X002500050024x}}</ref> ). There is close linkage to other genes in the [[Benzoxazinone biosynthesis|benzoxazinoid synthesis]] pathway [''bx2, bx3, bx4, bx5'' Frey et al. 1995,<ref name=Frey95>{{cite journal|last=Frey|first=M|author2=Kliem, R |author3=Saedler, H |author4= Gierl, A |title=Expression of a cytochrome P450 gene family in maize.|journal=Molecular & General Genetics|date=Jan 6, 1995|volume=246|issue=1|pages=100–9|pmid=7823905|doi=10.1007/bf00290138|s2cid=29908288}}</ref> 1997<ref name=Frey97 /> ). Gene ''bx1'' is 2490 [[base pair|bp]] from ''bx2'' (Frey et al. 1997<ref name=Frey97 /> ); between ''umc123'' and ''agrc94'' on 4S (Melanson et al. 1997<ref name=Melanson97>{{cite journal|last=Melanson|first=D|author2=Chilton, MD |author3=Masters-Moore, D |author4= Chilton, WS |title=A deletion in an indole synthase gene is responsible for the DIMBOA-deficient phenotype of bxbx maize.|journal=Proceedings of the National Academy of Sciences of the United States of America|date=Nov 25, 1997|volume=94|issue=24|pages=13345–50|pmid=9371848|doi=10.1073/pnas.94.24.13345|pmc=24311|bibcode=1997PNAS...9413345M|doi-access=free}}</ref> ). [[Genetic mapping|Mapping]] [[Genetic marker|probes]]: [[Simple Sequence Repeat|SSR]] p-umc1022 (Sharopova et al. 2002<ref name=Sharopova02>{{cite journal|last=Sharopova|first=N |author2=McMullen, MD |author3=Schultz, L |author4=Schroeder, S |author5=Sanchez-Villeda, H |author6=Gardiner, J |author7=Bergstrom, D |author8=Houchins, K |author9=Melia-Hancock, S |author10=Musket, T |author11=Duru, N |author12=Polacco, M |author13=Edwards, K |author14=Ruff, T |author15=Register, JC |author16=Brouwer, C |author17=Thompson, R |author18=Velasco, R |author19=Chin, E |author20=Lee, M |author21=Woodman-Clikeman, W |author22=Long, MJ |author23=Liscum, E |author24=Cone, K |author25=Davis, G |author26=Coe EH, Jr |title=Development and mapping of SSR markers for maize.|journal=Plant Molecular Biology|date=Mar–Apr 2002|volume=48|issue=5–6|pages=463–81|pmid=12004892|doi=10.1023/a:1014868625533 |s2cid=25157785 }}</ref> ); Overgo (physical map probe) PCO06449 (Gardiner et al. 2004<ref name=Gardiner04>{{cite journal|last=Gardiner|first=J |author2=Schroeder, S |author3=Polacco, ML |author4=Sanchez-Villeda, H |author5=Fang, Z |author6=Morgante, M |author7=Landewe, T |author8=Fengler, K |author9=Useche, F |author10=Hanafey, M |author11=Tingey, S |author12=Chou, H |author13=Wing, R |author14=Soderlund, C |author15=Coe EH, Jr |title=Anchoring 9,371 maize expressed sequence tagged unigenes to the bacterial artificial chromosome contig map by two-dimensional overgo hybridization.|journal=Plant Physiology|date=Apr 2004|volume=134|issue=4|pages=1317–26|pmid=15020742|doi=10.1104/pp.103.034538 |pmc=419808}}</ref> ).

== [[Phenotypes]] ==
Mutants are viable, but may be distinguished from normal plants by FeCl3 staining: plants able to synthesize benzoxinoids have pale blue color when crushed and treated with FeCl3 solutions (Hamilton 1964,<ref name=Hamilton64 /> Simcox 1993<ref name=Simcox93>{{cite journal|last=Simcox|first=KD|title=Screening large populations for recessive bx1 genotypes; a variation of the FeCl3 root-tip squash assay|journal=Maize Genetics Cooperation Newsletter|year=1993|volume=67|page=116|url=http://www.maizegdb.org/mnl/67/184simcox.html|accessdate=Dec 24, 2013}}</ref> ). [[Mutations]] in the ''bx1'' gene reduce the resistance to first generation [[European corn borer]] (''Ostrinia nubilalis'') that is conferred by [[DIMBOA|benzoxazinoids]] (Klun et al. 1970 <ref>{{Cite journal|last1=Klun|first1=Jerome A.|last2=Guthrie|first2=W. D.|last3=Hallauer|first3=Arnel R.|last4=Russell|first4=W. A.|date=1970|title=Genetic Nature of the Concentration of 2,4-dihydroxy-7-methoxy 2H-l,4-benzoxazin- 3(4H)-one and Resistance to the European Corn Borer in a Diallel Set of Eleven Maize Inbreds1|url=https://www.crops.org/publications/cs/abstracts/10/1/CS0100010087|journal=Crop Science|language=en|volume=10|issue=1|pages=87|doi=10.2135/cropsci1970.0011183X001000010032x|issn=0011-183X|url-access=subscription}}</ref>). ''Bx1'' mutant maize deposited less callose in response to [[chitosan]] elicitation than isogenic wildtype plants (Ahmad et al. 2011 <ref>{{Cite journal|last1=Ahmad|first1=Shakoor|last2=Veyrat|first2=Nathalie|last3=Gordon-Weeks|first3=Ruth|last4=Zhang|first4=Yuhua|last5=Martin|first5=Janet|last6=Smart|first6=Lesley|last7=Glauser|first7=Gaétan|last8=Erb|first8=Matthias|last9=Flors|first9=Victor|date=2011|title=Benzoxazinoid Metabolites Regulate Innate Immunity against Aphids and Fungi in Maize|journal=Plant Physiology|language=en|volume=157|issue=1|pages=317–327|doi=10.1104/pp.111.180224|pmid=21730199|issn=0032-0889|pmc=3165881}}</ref>). Genetic mapping using [[Recombinant inbred strain|recombinant inbred lines]] derived from maize inbred lines B73 and Mo17 showed that a 3.9 kb [[cis-regulatory element]] that is located approximately 140 kb upstream of ''Bx1'' causes higher 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one ([[DIMBOA]]) accumulation in Mo17 than in B73 seedlings (Zheng et al. 2015 <ref>{{Cite journal|last1=Zheng|first1=Linlin|last2=McMullen|first2=Michael D.|last3=Bauer|first3=Eva|last4=Schön|first4=Chris-Carolin|last5=Gierl|first5=Alfons|last6=Frey|first6=Monika|date=2015|title=Prolonged expression of the BX1 signature enzyme is associated with a recombination hotspot in the benzoxazinoid gene cluster in Zea mays|journal=Journal of Experimental Botany|language=en|volume=66|issue=13|pages=3917–3930|doi=10.1093/jxb/erv192|pmid=25969552|issn=1460-2431|pmc=4473990}}</ref>). This genetic variation is also associated with higher corn leaf aphid (''[[Rhopalosiphum maidis]]'') reproduction on B73 compared to Mo17 maize seedlings (Betsiashvili et al. 2014 <ref name=":0" />). Relative to maize inbred line W22'', Bx1::[[Ac/Ds transposable controlling elements|Ds]]'' mutant maize plants are more sensitive to corn leaf aphids (''[[Rhopalosiphum maidis]]'') (Betsiashvili et al. 2014<ref name=":0" />) and beet armyworms (''[[Spodoptera exigua]]'') (Tzin et al. 2017 <ref>{{Cite journal|last1=Tzin|first1=Vered|last2=Hojo|first2=Yuko|last3=Strickler|first3=Susan R|last4=Bartsch|first4=Lee J|last5=Archer|first5=Cairo M|last6=Ahern|first6=Kevin R|last7=Zhou|first7=Shaoqun|last8=Christensen|first8=Shawn A|last9=Galis|first9=Ivan|date=2017|title=Rapid defense responses in maize leaves induced by Spodoptera exigua caterpillar feeding|journal=Journal of Experimental Botany|language=en|volume=68|issue=16|pages=4709–4723|doi=10.1093/jxb/erx274|pmid=28981781|issn=0022-0957|pmc=5853842}}</ref>). Highly localized induction of benzoxazinoid accumulation in response to Egyptian cotton leafworm (''[[Spodoptera littoralis]]'') feeding is abolished in a maize ''bx1'' mutant (Maag et al. 2016 <ref>{{Cite journal|last1=Maag|first1=Daniel|last2=Köhler|first2=Angela|last3=Robert|first3=Christelle A.M.|last4=Frey|first4=Monika|last5=Wolfender|first5=Jean-Luc|last6=Turlings|first6=Ted C.J.|last7=Glauser|first7=Gaétan|last8=Erb|first8=Matthias|date=2016|title=Highly localized and persistent induction of Bx1 -dependent herbivore resistance factors in maize|journal=The Plant Journal|language=en|volume=88|issue=6|pages=976–991|doi=10.1111/tpj.13308|pmid=27538820|bibcode=2016PlJ....88..976M |doi-access=free}}</ref>).

== Gene Product ==
Catalyzes the first step in the [[Benzoxazinone biosynthesis|synthesis]] of [[DIMBOA]], forming [[indole]] from indole-3-glycerol phosphate. The [[enzyme]] is called [[Indole-3-glycerol-phosphate lyase|indole-3-glycerol phosphate lyase]], [[chloroplast]], EC 4.1.2.8 and is located in the [[chloroplast]]. The [[X-ray structure]] of BX1 protein has been resolved and compared with bacterial TSA ([[tryptophan synthase]] alpha subunit, Kulik et al. 2005).<ref name=Kulik05>{{cite journal|last=Kulik|first=V|author2=Hartmann, E |author3=Weyand, M |author4=Frey, M |author5=Gierl, A |author6=Niks, D |author7=Dunn, MF |author8= Schlichting, I |title=On the structural basis of the catalytic mechanism and the regulation of the alpha subunit of tryptophan synthase (TSA) from Salmonella typhimurium and BX1 from maize, two evolutionarily related enzymes.|journal=Journal of Molecular Biology|date=Sep 23, 2005|volume=352|issue=3|pages=608–20|pmid=16120446|doi=10.1016/j.jmb.2005.07.014}}</ref> Three [[homologs]] of the BX1 [[protein]] occur in maize. One is encoded by the gene ''tsa1'', ''tryptophan synthase alpha1''(Frey et al. 1997,<ref name=Frey97 /> Melanson et al. 1997<ref name=Melanson97 /> ), on chromosome 7, another by ''igl1'', ''indole-3-glycerol phosphate lyase1''(Frey et al. 1997,<ref name=Frey97 /> on chromosome 1, and another by ''tsah1'', 'TSA like" and located near the ''bx1'' gene (Frey et al. 1997.<ref name=Frey97 /> ).

== Links ==
* [http://www.maizegdb.org/cgi-bin/displaylocusrecord.cgi?id=12097 MaizeGDB]
* [https://www.ncbi.nlm.nih.gov/gene?cmd=search&term=542117 NCBI]
* [https://www.uniprot.org/uniprot/P42390 Uniprot]

==References==
{{reflist}}

[[Category:Biochemistry]]
[[Category:Genetics]]

Bx1 benzoxazin1 - История изменений

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