46. Relationship between transposon and mutability caused by hybrid dysgenesis in rice

Y. TSUCHIMINE1, Y. MIYASHITA1, R. ISHIKAWA 1, M. SENDA2, S. AKADA2, T. HARADA1 and M. NIIZEKI1

1) Faculty of Agriculture. Hirosaki University, Hirosaki, 036 Japan
2) Gene Research Center, Hirosaki University, Hirosaki, 036 Japan

High instability was noted in the progeny of a cross between Japonica strains and a particular Indica strain (Acc435) which originated from Sri Lanka. We found maize Mutator-like transposon in rice (RMu1 IR36). We tried to find a relationship between the hybrid dysgenesis and the activity of rice RMu family in the hybrid progeny. We used five reciprocal crosses consisting of ten F2 populations of crosses between the Indica strain Acc435 and five Japonica strains. We observed mutation rate at third leaf stage (Table 1). Chlorophyll mutants were easily detected, which included striata (0.4%), albinos (0.2%) and virescents (0.04%). In addition, 0.2% plants were aborted and some morphological mutants were found, for examples, tall, twin shoot, and shootless.

Southern hybridization analysis was carried out using ten related progenies originating from Acc435. Several kinds of RFLP patterns were found (Fig. 1). As the Acc435 did not show any RT-PCR product of ORF in Rmu1 with cDNA templates from mature leaves, this mutability within the strain may be kept at lower level than usual state. The mutability would be increased by genomic shock when crossed with Japonica strains in which abundant RT-PCR products of ORF in Rmu1 has been known (Ishikawa, unpublished data).

Several kinds of hybrid dysgenesis have been known in Drosophila such as P-M hybrid dysgenesis caused by re-activation of transposable elements. And also in maize, high mutability was gained when mutable strains carrying active Mutator were crossed with stable lines carrying non-autonomous Mutator members. Thus we suggest that the hybrid dysgenesis phenomenon found in rice would be caused by Rice Mutator which are activated by crossing with other strains carrying an active element.


Table 1. Mutation rate in reciprocal crosses consisting F2 populations between
Indica Acc435 and five Japonica strains
Cross combination
Total plants
No.of aborted
Plants (∼3rd
leaf) (%)
Total
mutants
(%)
No.of mutants concerning to leaf
Striata(%)
Albino(%) 
Virescent(%)
Acc435 X L119
L119 X Acc435
1061
1127
76 ( 7.2)
135 (12.0)
21 (2.0)
14 (1.2)
6 (0.6) 
0 (0.0)
1 (0.1)
1 (0.1)
0 (0.0)
0 (0.0)
Acc435 X Oou195
Oou195 X Acc435
638 664
2 ( 0.3) 
102 (15.4)
8 (1.3)
10(1.5)
2 (0.3)
1 (0.2)
2 (0.3)
6 (0.9)
1 (0.2)
0 (0.0)
Acc435 X Acc504
Acc504 X Acc435
704
698
237 (33.7)
116 (16.6)
26 (3.7)
12 (1.7)
1 (0.1)
2 (0.3)
2 (0.3)
0 (0.0)
0 (0.0)
0 (0.0)
Acc435 X T65(Hg)
T65(Hg) X Acc435
961
1055
80 ( 8.3)
10 ( 0.9)
32 (3.3)
25 (2.4)
7 (0.7)
8 (0.8)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
Acc435 X E18
E18 X Acc435
156
141
36 (23.1)
115 (81.6)
2 (1.3)
3 (2.1)
0 (0.0)
0 (0.0)
0 (0.0)
1 (0.7)
0 (0.0)
0 (0.0)

Fig. 1. RFLPs detected in self-pollinated progeny of Acc435. Genomic DNA was digested with Xho I (lanes 1 to 10) and Xmn I (lanes 11 to 12). Blot was hybridized with TNP domain of RMu1. Lanes 1 to 10 and lanes 11 to 20 were corresponding different families in the progeny of single Acc435 accession.