GENERATION OF HAPOLOID PLANTS BASED ON KNL2

Abstract

Non-transgenic and transgenic plants, preferably crop plants, comprising at least one mutation of the KINTEOCHORE NULL2 (KNL2) protein, especially a mutation causing a substitution of an amino acid within the KNL2 protein, preferably within the C-terminal region of the KNL2 protein, which preferably have the biological activity of a haploid inducer. Further are methods of generating plants and haploid and double haploid plants obtainable by crossing non-transgenic and transgenic plants with wildtype plants as well as methods of facilitating cytoplasm exchange.

Claims

1. A plant, wherein the plant comprises a nucleotide sequence encoding a KINETOCHORE NULL2 (KNL2) protein comprising a CENPC-k motif, wherein the nucleotide sequence comprises at least one mutation in the CENPC-k motif encoding sequence, and wherein the plant is a crop or agricultural plant or ornamental flower or ornamental crop.

2. The plant according to claim 1, wherein the at least one mutation is a deletion, addition or substitution of at least one nucleotide in the nucleotide sequence for the CENPC-k motif.

3. The plant according to claim 1, wherein the plant has biological activity of a haploid inducer.

4. The plant according to claim 1, wherein the plant is sunflower, peanut, corn, potato, sweet potato, bean, pea, chicory, lettuce, endive, cabbage, cauliflower, broccoli, turnip, radish, spinach, onion, garlic, eggplant, celery, carrot, squash, pumpkin, zucchini, cucumber, apple, pear, melon, strawberry, grape, raspberry, pineapple, soybean, Cannabis, Humulus (hop), tomato, sorghum, sugar cane, in particular maize, wheat, barley, sorghum, rye, oats, turf and forage grasses, millet, rice and sugar cane.

5. The plant according to claim 1, wherein the plant expresses a KNL2 protein having at least one amino acid addition, amino acid deletion and/or amino acid substitution in the CENPC-k motif.

6. The plant according to claim 1, wherein the KNL2 protein comprises an amino acid sequence according to one of SEQ ID No. 23 to SEQ ID No. 123 or SEQ ID No. 164 to SEQ ID No. 274.

7. The plant according to claim 1, wherein the amino acid arginine at position 10 of SEQ ID No. 4 to SEQ ID No. 22 is substituted, preferably substituted for alanine and/or wherein the amino acid tryptophan at position 19 of SEQ ID No. 4 to SEQ ID No. 22 is substituted, preferably substituted for arginine or wherein the amino acid arginine at position 8 or 7 or 6 of SEQ ID No. 127 to SEQ ID No. 163 is substituted, preferably substituted for alanine and/or wherein the amino acid tryptophan at position 17 or 16 or 15 of SEQ ID No. 4 to SEQ ID No. 22 is substituted, preferably substituted for arginine.

8. The plant according to claim 1, wherein the wildtype CENPC-k motif comprises an amino acid sequence according to one of SEQ ID No. 124 to SEQ ID No. 126.

9. The plant according to claim 1, wherein the non-mutated CENPC-k motif comprises an amino acid sequence according to table 1 or table 2 or table 3.

10. A part of the plant according to claim 1, where in the part is a shoot vegetative organ, root, flower or floral organ, seed, fruit, ovule, embryo, plant tissue or cell.

11. A haploid plant obtainable by crossing the plant of claim 1 with a plant expressing wildtype KNL2 protein.

12. A double haploid plant obtainable by converting the haploid plant according to claim 11 into a double haploid plant, preferably via colchicine treatment.

13. A haploid plant obtainable by crossing in a first step the plant according to any of claim 1 with a plant comprising a nucleotide sequence encoding a centromer histone H3 (CENH3) protein comprising a CATD domain, wherein the nucleotide sequence comprises at least one mutation causing in the CATD domain an amino acid substitution which confers the biological activity of a haploid inducer, and crossing in a second step a plant obtained in the first step with a plant expressing wildtype KNL2 protein and wildtype CENH3 protein.

14. A double haploid plant obtainable by converting the haploid plant according to claim 13 into a double haploid plant, preferably via colchicine treatment.

15. A plant having biological activity of a haploid inducer and comprising a nucleotide sequence encoding a KINETOCHORE NULL2 (KNL2) protein, wherein the nucleotide sequence comprises at least one mutation.

16. A nucleotide sequence encoding at least the C-terminal part of KNL2 protein comprising at least one mutation causing an amino acid substitution, deletion or addition, preferably in the CENPC-k motif.

17. A plant cell or host cell comprising the nucleotide sequence of claim 16 or an according vector as a transgene.

Description

[0535] The figures show:

[0536] FIG. 1a shows an alignment of the CENP-C motif of the A. thaliana CENP-C protein (SEQ ID No. 2) and the CENP-C like motif of A. thaliana KNL2 protein (SEQ ID No. 4);

[0537] FIG. 1b shows an alignment of the CENP-C like motifs of KNL2 homologues of different plants;

[0538] FIG. 2 shows a flow cytometry analysis of Arabidopsis thaliana seeds after crossing of knI2 mutant as female with the wild type male.

[0539] FIG. 3 shows a consensus sequence of the CENPC-k motif for plants (A), monocotyledonous plants (B) and diocotyledonous plants (C) as outlined in SEQ ID No. 124 to SEQ ID No. 126.

EXAMPLES

Example 1

[0540] A flow cytometry analysis of Arabidopsis thaliana seeds after crossing of kn12 mutant as female with the wild type male was done. For each sample 10 seeds were pooled together. Haploid picks are indicated on each histogram as shown in FIG. 2. Haploid induction efficiency was ˜10%.

Example 2

[0541] The CENPC-k motif is required for the centromeric localization of KNL2 and functionally it can be replaced by the CENPC motif of CENP-C

[0542] Mutational analysis has identified critical residues of the CENPC or the CENPC-v motif that are essential for centromeric localization of CENP-C, or for H3/cenH3 nucleosome binding. Two of these correspond to residues R546 and W555 of the Arabidopsis CENPC-k motif. The wild type C-terminal part of KNL2 fused to EYFP can localize to. R546 and W555 were mutated in this construct (KNL2(C)CENPC-k(R-A) and KNL2(C)CENPC-k(W-R)) to determine whether CENPC-k plays a similar role in KNL2 to the role of the CENPC and CENPC-v motifs in CENP-C. Additionally, the construct with complete deletion of the CENPC-k motif (KNL2(C)ΔCENPC-k) was generated. Analysis of transgenic A. thaliana plants expressing these constructs showed that the mutagenized KNL2 variants are unable to localize to chromocenters/centromeric sites. Fluorescence signals were detected in nucleoplasm and in nucleoli. These results suggest that the CENPC-k motif of KNL2 in general, and the conserved 8546 and W555 amino acids in particular, are required for in vivo localization of KNL2 at centromeres of A. thaliana.

[0543] The inventors addressed the question whether replacement of CENPC-k by the CENPC motif of A. thaliana CENP-C(KNL2(C)CENPC) will restore the ability of KNL2(C)ΔCENPC-k to localize to centromeres. Analysis of transgenic A. thaliana plants expressing the KNL2(C)CENPC construct has revealed that the CENPC motif is indeed able to target KNL2 to centromeres. Fluorescence signals were detected in nucleoplasm and at centromeres similar to the KNL2(C) control. In contrast to the mutagenized KNL2(C) variants, no fluorescence was detected in the nucleolus. These data suggest that CENPC motifs of KNL2 and of CENP-C proteins might play the same role in recognition of centromeric nucleosomes.

[0544] Additionally, leaves of Nicotiana benthamiana were transiently transformed by Agrobacterium tumefaciens with constructs expressing the wild type C-terminal part of KNL2, KNL2(C)ΔCENPC-k or KNL2(C)CENPC in a fusion with EYFP at their N- or C-termini, respectively. These constructs were expressed in N. benthamiana alone or in a combination with cenH3-mCherry. It was shown that in some cells the chimeric KNL2(C)CENPC protein is localizing to centromeres and co-localizing with cenH3 similar to the KNL2(C) with the native CENPC-k motif, while KNL2(C)ΔCENPC-k protein was detected only in nucleoplasm and nucleolus. These data demonstrate that A. thaliana KNL2 can be targeted to centromeres of distantly related species such as N. benthamiana and that centromeric targeting requires presence of CENPC-k or CENPC motifs.

Example 3

[0545] The C-terminal part of A. thaliana KNL2 binds the centromeric repeat pAL1 DNA in vitro.

[0546] To test whether A. thaliana KNL2 interacts with the centromeric DNA despite of the absence of a distinct SANT/Myb domain, an electrophoretic-mobility shift assay (EMSA) with recombinant KNL2 protein fragments and centromeric repeat pAL1 DNA was performed. The N-terminal part of KNL2 including the SANTA domain and the C-terminus with the CENPC-k motif in fusion with a His-tag were separately expressed in E. coli. Soluble proteins were purified under non-denaturation conditions and used for a non-radioactive EMSA experiment with the centromeric repeat pAL1. The results showed that the mobility of pAL1 is shifted upwards only in the presence of recombinant C-, but not the N-terminal part of KNL2. The effect of KNL2(C) concentration on DNA binding was tested using constant amounts of pAL1 DNA and increased amounts of protein. The mobility of a portion of pAL1 DNA slightly shifted in cases of DNA:protein ratio 1:1 and 1:2, respectively, but with an increased amount of protein all pAL1 DNA was shifted upwards suggesting that one molecule of pAL DNA may be bound by several molecules of KNL2. In case of KNL2(N) no DNA binding was observed even in high excess of protein (DNA:protein 1:8) was applied. Additionally, to the non-radioactive EMSA, we have employed the more commonly used radioactive variant and received similar results indicating that both methods have similar sensitivity.

Example 4

[0547] KNL2 binds non-centromeric sequences in vitro, but in vivo it associates preferentially with the centromeric repeat pAL1

[0548] To test whether the C-terminus of KNL2 interacts preferentially with centromeric repeats, we performed a competition experiment in which poly(deoxyinosinic-deoxycytidylic) acid (poly dI/dC) was used. The DNA binding capability of the C-terminal KNL2 to pAL1 was abolished by 50 ng/μl poly dI/dC. About 1-2.5 ng/μl poly dI/dC are usually used in EMSA to inhibit unspecific interactions. Next, we analyzed the interaction of KNL2(C) with repetitive elements such as the centromeric transposable element Athila, the telomeric repeat and the coding region of tubulin. The data showed that the C-terminus of KNL2 binds all non-centromeric DNA sequences that were used, albeit in a competition assay the euchromatic tubulin sequence TUA4 was bound with lower strength than repetitive sequences. Earlier it was shown that also CENP-C of maize binds DNA sequence-independently and that this DNA binding capability is stabilized by transcribed centromeric repeats and by small single stranded centromeric RNAs (ssRNAs). The inventors have identified a 23 nt ssRNA sequence for the centromeric repeat pAL1 from small RNA seq data of the wildtype and tested whether this ssRNA interacts with KNL2 and influences its binding capability to pAL1 in EMSA. However, the selected ssRNA showed an interaction with KNL2, but had no effect on binding of pAL1 by KNL2.

[0549] To analyze the interaction of KNL2 with DNA in vivo, chromatin immunoprecipitation (ChIP) was performed. Antibodies against KNL2 were purified by affinity chromatography and applied to chromatin isolated from seedlings of A. thaliana wild-type plants. Results showed that in vivo KNL2 binds preferentially the centromeric repeat pAL1 and to a much lower extent is associated with other sequences.