1. Zea mays Viviparous 1 (vp1) Gene
Jon Scales Genetics Fall 2016
Introduction
The viviparous-1 (vp1) mutation in Zea mays causes embryos to germinate precociously while still attached to the ear (Fig 1). The normal function of the protein functions to place the embryo into a state of dormancy during which the kernel desiccates prior to normal germination. In addition to the pre-cocial germination, vp1 kernels lack aleurone and pericarp pigmentation. If the kernels are removed from the ear after precocial ger-mination and planted prior to desiccation, they remain viable and produce fertile plants. Eight other mutations have been identified which also control embryo dormancy, all of which have been shown to reduce the levels of abscisic acid (ABA), a plant hormone. Vp1 however, does not reduce ABA production. Other viviparous-like mutations, can be res-cued by treatment with ABA, but vp1 mutants are not. `
Gene Model
Molecular Nature of Mutation
Vp1 is a classically obtained mutation in maize. The vp1-mum1 allele was produced as a transposon-induced mutation using the Ro-bertson mutator (Mu). The presence of the transposon sequences within the vp1 locus allowed the genomic DNA spanning the vp1 locus to be cloned. Additional Mu-element tagged alleles (vp1-Mc and vp1-mum2 were generated that had mutant pigment pheno-types, but did not cause premature ger-mination. The insertion points of the Mu ele-ments are shown in fig 3. The Mu insertions all disrupt the reading frames and cause pre-mature termination of translation and trun-cated proteins. A B
CTACACCCGAGAGGCGGCGGCGGCAGACACAGACACCGTCTCTCTCCTCCCTTTGTCGTCGTGCCTCTCTGCATGGAAGCCTCCTCCGGC
M E A S S G
TCGTCGCCACCGCACTCCCAAGAGAACCCGCCGGAGCACGGTGGCGACATGGGAGGGGCCCCCGCGGAGGAGATCGGAGGGGAGGCGGCG
S S P P H S Q E N P P E H G G D M G G A P A E E I G G E A A
GATGACTTCATGTTCGCTGAAGACACGTTCCCCTCCCTCCCGGACTTCCCTTGCCTTTCGTCGCCGTCCAGCTCCACCTTCTCGTCCAAC
D D F M F A E D T F P S L P D F P C L S S P S S S T F S S N
TCCTCGTCAAACTCCTCCAGCGCCTACACCAACACGGCAGGAAGAGCCGGCGGCGAGCCCTCCGAGCCTGCTTCGGCCGGAGAAGGGTTT
S S S N S S S A Y T N T A G R A G G E P S E P A S A G E G F
GATGCGCTCGATGACATCGACCAGCTCCTCGACTTCGCGTCGCTTTCCATGCCGTGGGACTCCGAGCCGTTCCCGGGGGTTAGCATGATG
D A L D D I D Q L L D F A S L S M P W D S E P F P G V S M M
CTAGAGAACGCCATGTCGGCGCCGCCGCAGCCGGTGGGCGACGGCATGAGTGAAGAGAAAGCCGTGCCGGAAGGGACCACGGGGGGAGAG
L E N A M S A P P Q P V G D G M S E E K A V P E G T T G G E
GAGGCCTGCATGGATGCGTCGGAGGGGGAGGAGCTGCCGCGGTTCTTCATGGAGTGGCTCACGAGCAACCGCGAAAACATCTCGGCCGAG
E A C M D A S E G E E L P R F F M E W L T S N R E N I S A E
GATCTCCGCGGGATCCGCCTCCGCCGCTCCACCATCGAGGCCGCCGCCGCCCGGCTCGGCGGCGGGCGCCAGGGCACCATGCAGCTGCTC
D L R G I R L R R S T I E A A A A R L G G G R Q G T M Q L L
AAGCTCATCCTCACCTGGGTGCAGAACCACCACCTCCAGAGGAAGCGCCCGCGCGACGTGATGGAGGAGGAGGCGGGCCTGCACGTCCAG
K L I L T W V Q N H H L Q R K R P R D V M E E E A G L H V Q
CTCCCCAGCCCGGTCGCCAACCCACCAGGATACGAGTTCCCCGCCGGCGGACAGGACATGGCCGCGGGCGGCGGCACATCTTGGATGCCC
L P S P V A N P P G Y E F P A G G Q D M A A G G G T S W M P
CACCAGCAGGCATTCACGCCGCCTGCTGCGTACGGCGGCGACGCGGTGTACCCGAGCGCGGCAGGCCAACAGTACTCTTTCCACCAGGGC
H Q Q A F T P P A A Y G G D A V Y P S A A G Q Q Y S F H Q G
CCCAGCACGAGCAGCGTGGTCGTGAACAGCCAACCGTTCTCCCCGCCGCCTGTGGGCGACATGCACGGCGCGAACATGGCCTGGCCGCAG
P S T S S V V V N S Q P F S P P P V G D M H G A N M A W P Q
CAGTACGTGCCGTTCCCACCGCCTGGGGCTTCCACGGGCTCTTACCCTATGCCGCAGCCGTTCTCCCCCGGATTCGGCGGGCAGTACGCC
Q Y V P F P P P G A S T G S Y P M P Q P F S P G F G G Q Y A
GGCGCCGGCGCTGGCCACCTCTCAGTGGCCCCCCAGCGCATGGCAGGCGTGGAGGCCTCGGCGACCAAGGAGGCCCGCAAGAAGCGCATG
G A G A G H L S V A P Q R M A G V E A S A T K E A R K K R M
GCGAGACAGCGGCGCCTGTCCTGCCTGCAGCAGCAGCGCAGCCAGCAGCTGAGCCTGGGCCAGATCCAGACCTCCGTCCACCTGCAGGAG
A R Q R R L S C L Q Q Q R S Q Q L S L G Q I Q T S V H L Q E
CCGTCCCCTCGGTCCACGCACTCCGGCCCGGTCACGCCGTCAGCAGGCGGCTGGGGATTCTGGTCGCCGAGCAGCCAGCAGCAGGTCCAG
P S P R S T H S G P V T P S A G G W G F W S P S S Q Q Q V Q
AACCCGCTCTCCAAGTCCAATTCCTCAAGGGCGCCGCCTTCCTCGCTGGAAGCGGCGGCGGCGGCTCCACAGACAAAGCCCGCGCCTGCT
N P L S K S N S S R A P P S S L E A A A A A P Q T K P A P A
GGTGCTCGGCAGGACGACATTCACCACCGCCTCGCAGCGGCTTCAGATAAGCGGCAGGGCGCCAAGGCGGACAAGAACCTGCGGTTCCTG
G A R Q D D I H H R L A A A S D K R Q G A K A D K N L R F L
CTGCAGAAGGTGCTGAAGCAGAGCGACGTCGGGAGCCTCGGCCGCATCGTGCTCCCCAAAAAGGAAGCGGAGGTTCACCTGCCGGAGCTG
L Q K V L K Q S D V G S L G R I V L P K K E A E V H L P E L
AAGACGAGGGATGGCATCTCCATCCCCATGGAGGACATCGGAACGTCGCGCGTGTGGAACATGCGGTACAGGTTTTGGCCCAACAACAAG
K T R D G I S I P M E D I G T S R V W N M R Y R F W P N N K
AGCAGAATGTATCTGCTGGAAAACACAGGGGAATTTGTTCGTTCCAACGAGCTTCAGGAGGGGGATTTCATAGTGATCTACTCCGATGTC
S R M Y L L E N T G E F V R S N E L Q E G D F I V I Y S D V
AAGTCGGGCAAATATCTGATACGGGGCGTGAAGGTAAGGCCCCCGCCGGCGCAAGAGCAAGGCAGTGGTTCCAGCGGGGGAGGCAAGCAC
K S G K Y L I R G V K V R P P P A Q E Q G S G S S G G G K H
AGGCCCCTCTGTCCAGCAGGTCCAGAGAGAGCCGCAGCCGCCGGTGCTCCTGAAGACGCCGTCGTCGACGGGGTCAGCGGCGCCTGCAAG
R P L C P A G P E R A A A A G A P E D A V V D G V S G A C K
GGGAGGTCTCCGGAAGGCGTGCGGCGGGTTCGGCAGCAGGGAGCCGGCGCCATGAGCCAGATGGCGGTGAGCATCTGAAAGAGCAGCAGG
G R S P E G V R R V R Q Q G A G A M S Q M A V S I
CTCCGCCATATATTGATCGATCGACCAATCGATCGTTAGTTCTCCAAGTTACTATTAGCTAGCTATAGCCCGAAACAGCTGAACTGATGA
TGACGATGGTAACCTCCGTCGTGTGTGTGCTAAGCATGTAGCGTGCTAGGAGATGATATATTAAATATAATCGAGTAGTAGAGCCTACCC
GCTGTGTGACGCTAAATTTGTGTGCATTTGGTTTGGTTTGTGAGTTGGGCCCGTGCGTGGCTGTGTCATGTCGTGGTTAATTAGCTATAC
TAGTCCTGTCTGTACATGCATGGACA
Figure 3. Mu transposon insertions into the vp1 locus.
Figure 2. Structure of the vp1 gene in Zea mays. A) The gene spans 5044bp and comprises 6 exons. B) The gene expresses a 2500nt mRNA that encodes a 691 amino acid protein. The protein is a transcriptional regulator. The B3-family DNA binding domain (aa ) is underlined and bolded. The acidic transcriptional activation domain (aa 1-121) is shown in bold italics.
Biological Function of vp1
The viviparous-1 gene encodes a transcription factor with a B3 family DNA binding domain. The B3 domain is unique to plant transcription factors. The amino terminus of the protein contains an acidic activation domain. The vp1 protein appears to regulate the transcription of numerous genes involved in abscisic acid (ABA) induced development of the maize embryo. Because vp1 mutants are not respon-sive to treatment with ABA, vp1 is thought to be activated by ABA and mediate the down-stream affects of that hormone.
References
McCarty DR, et al, 1991, The Viviparous-1 developmental gene of maize encodes a novel transcriptional activator, Cell 66:895.
McCarty DR, et al., 1989, Molecular analysis of viviparous-1: an absinic acid insensitive mutant of maize, Plant Cell 1:523.
McCarty, DR, et al., 1989, Transposable element-induced mutations of the viviparous-1 gene in maize, Dev Gen 10:473.
Figure 1. Wildtype (left) and viviparous-1 (right) ears. Mutant kernels germinate while still on the ear. Mutant kernels also lack pigmentation, making them detect-able before they germinate.