Identification of the Core Pollen-Specific Regulation in the Rice OsSUT3 Promoter.

The regulatory mechanisms of pollen development have potential value for applications in agriculture, such as better understanding plant reproductive regularity. Pollen-specific promoters are of vital importance for the ectopic expression of functional genes associated with pollen development in plants. However, there is a limited number of successful applications using pollen-specific promoters in genetic engineering for crop breeding and hybrid generation. Our previous work led to the identification and isolation of the OsSUT3 promoter from rice. In this study, to analyze the effects of different putative regulatory motifs in the OsSUT3 promoter, a series of promoter deletions were fused to a GUS reporter gene and then stably introduced into rice and Arabidopsis. Histochemical GUS analysis of transgenic plants revealed that p385 (from -385 to -1) specifically mediated maximal GUS expression in pollen tissues. The S region (from -385 to -203) was the key region for controlling the pollen-specific expression of a downstream gene. The E1 (-967 to -606), E2 (-202 to -120), and E3 (-119 to -1) regions enhanced ectopic promoter activity to different degrees. Moreover, the p385 promoter could alter the expression pattern of the 35S promoter and improve its activity when they were fused together. In summary, the p385 promoter, a short and high-activity promoter, can function to drive pollen-specific expression of transgenes in monocotyledon and dicotyledon transformation experiments.

Characterization of a new semi-dominant dwarf allele of SLR1 and its potential application in hybrid rice breeding.

The widespread introduction of semi-dwarf1 (sd1), also known as the 'Green Revolution' gene, has dramatically increased rice yield. However, the extensive use of limited sources of dwarf genes may cause 'bottleneck' effects in breeding new rice varieties. Alternative dwarf germplasms are quite urgent for rice breeding. Here, we characterized a new allele of the rice Slr1-d mutant, Slr1-d6, which reduced plant height by 37%, a much milder allele for dwarfism. Slr-d6 was still responsive to gibberellin (GA) to a reduced extent. The mutation site in Slr1-d6 was less conserved in the TVHYNP domain, leading to the specific semi-dominant dwarf phenotype. Expression of SLR1 and five key GA biosynthetic genes was disturbed in Slr1-d6, and the interaction between Slr1-d6 and GID1 was decreased. In the genetic background of cultivar 9311 with sd1 eliminated, Slr1-d6 homozygous plants were ~70 cm tall. Moreover, Slr1-d6 heterozygous plants were equivalent in height to the standard sd1 semi-dwarf 9311, but with a 25% yield increase, showing its potential application in hybrid rice breeding.

OsSDS is essential for DSB formation in rice meiosis.

SDS is a meiosis specific cyclin-like protein and required for DMC1 mediated double-strand break (DSB) repairing in Arabidopsis. Here, we found its rice homolog, OsSDS, is essential for meiotic DSB formation. The Ossds mutant is normal in vegetative growth but both male and female gametes are inviable. The Ossds meiocytes exhibit severe defects in homologous pairing and synapsis. No γH2AX immunosignals in Ossds meiocytes together with the suppression of chromosome fragmentation in Ossds-1 Osrad51c, both provide strong evidences that OsSDS is essential for meiotic DSB formation. Immunostaining investigations revealed that meiotic chromosome axes are normally formed but both SC installation and localization of recombination elements are failed in Ossds. We suspected that this cyclin protein has been differentiated pretty much between monocots and dicots on its function in meiosis.

Segregation distortion detected in six rice F2 populations generated from reciprocal hybrids at three altitudes.

This paper presents investigations of segregation distortion of six rice F2 populations generated from reciprocal F1 hybrids grown at three locations varied at altitudes from 400 to 2200 m. The F1s were derived from reciprocal crosses between cv. XMG, which is a japonica landrace traditionally grown at 2650 m altitude, and cv. N34, which is a japonica restorer possessing a fertility restoring (Rf) gene and cytoplasm of male sterility (CMS) donated by an indica cultivar. Among nine morphological traits of the F2 populations, only one was in normal distribution, eight were distorted in all or at least one population. Out of 16 polymorphic PCR markers, 10 markers distributed on 7 chromosomes were significantly distorted. Among these markers, RMAN7 and RM257 were distorted in both of the reciprocal populations, which suggested that nuclear genes had strong effects on segregation distortion. The other makers were distorted only in the populations with cytoplasm donated by XMG or N34. The results indicated that segregation of DNA markers was affected by cytoplasm background. Segregation distribution was also affected by altitude, since segregation distortions of most of the markers were detected not in all the three populations generated from F1 grown at the three altitudes, but only in one population from F1 grown at one altitude. Marker M45461, which is located within Rf-1 locus, was severely distorted towards N34 in all the populations with cytoplasm donated by N34, but not in the populations with cytoplasm provided by XMG. The results indicated that interaction between CMS and Rf gene had strong effects on distortion. Results of this study indicated that japonica cytoplasm did not cause distortion favouring a special parent, but indica cytoplasm made distortion favouring a maternal parent. The results suggested that indica cytoplasm was not well compatible with japonica nuclear background, while japonica cytoplasm did not have such trouble with indica nuclei. This study also found that the six F2 populations were divergent into two groups due to difference of cytoplasm background.

RFLP analysis for mitochondrial genome of CMS-rice.

Restriction fragment length polymorphism (RFLP) was used to analyze mitochondrial (mt) genome of cytoplasmic male sterility (CMS) rice. Differences were observed among mitochondrial genomes of the sterile line (A) and maintain line (B) of nine types of CMS rice; Mitochondrial genomic differences were also detected between A and B in many functional gene regions. Even the materials with the same nucleic background have differences in their mtDNA. This provides molecular evidence for the cytoplasmic heterogeneity and the CMS mechanism research.

[Relationship between genetic lineage and pathotype of Pyricularia grisea in Yunnan Plateau].

Rice blast caused by Pyricularia grisea is the most destructive disease in Yunnan Plateau, China. In order to elucidate the relationship between genetic lineage and pathotype of P. grisea of Yunnan Plateau as well as the variability of the fungus at DNA level,the repetitive element-based PCR (rep-PCR) of Pot2, an element found in approximately 100 copies in the fungus genome,was exploited. Two hundred and thirty-six isolates of P. grisea collected from 15 main rice-growing counties of Yunnan Plateau were fingerprinted by using rep-PCR. A linkage graph of the rep-PCR fingerprints from 134 representative isolates was generated using an unweighted pair-grouped average program (UPGMA) of the STATISTICAL 5.0 software. The isolates were classified into 8 genetic lineages (G1 approximately G8) at the level of 1.75 genetic linkage distance, of which the G1, G2 and G4 were the dominant lineages. The isolates in a certain area generally belonged to one correspondent genetic lineage and the isolates from the same plot and host rice variety mostly shared one linkage group though different genetic lineages within one lesion. Furthermore, 29 isolates representing the eight genetic lineages were inoculated on 33 rice cultivars of Yunnan at the stage of 3 approximately 4 leaves in greenhouse. The isolates were divided into 6 pathotype groups (P1 approximately P6) according to its compatibility, which demonstrated that some isolates of one genetic lineage sharing two or three pathotype groups, alternatively, one or four pathotype groups. The isolates from each genetic lineage, however, may share one pathotype group such as P2. The preliminary results implicated that the relationship between genetic lineages and pathotype groups of P. grisea in Yunnan Plateau was complicated rather than simple. On the other hand,2 rice cultivars including HeXi 16 and JingGuo 92 were resistant to the 29 isolates but YunJing 20 and HeXi 30 both susceptible to all of them, which was helpful for deploying the blast-resistant genes in rice production of Yunnan Plateau. Therefore, the rice blast-resistance spectrum of the tentative new rice cultivars should be evaluated before its release considering the blast-resistant rice breeding and the practice of rice production in Yunnan Plateau.