5. Application potential analyses of BMS systems by using GMS genes in crop plants

As described above, cloning and characterization of plant GMS genes have contributed significantly to our understanding of the molecular mechanisms of

with antisense and CRISPR-Cas9 systems and cytological characterization of mutants by transverse section observation and TEM analysis of anthers at different stages [84, 85]. The functions of wheat TaMs26 in anther and pollen wall development in bread wheat were tested by targeted mutagenesis of all the three homologs and cytological analysis using SEM method [77]. Cytological observation is helpful to confirm the function mechanism of the putative GMS genes in the cellular level.

4. Application value evaluation of GMS genes and mutants

heterosis comparison, and analysis of potential linkage with bad traits.

4.1 Genetic stability analysis of male-sterility

The application value evaluation of GMS genes and mutants in crop plants.

Compared to CMS and environment-sensitive genic male sterility (EGMS), GMS

Firstly, the genetic stability of the male-sterile mutant should be appraised in different genetic backgrounds and various environments. The general procedure is as follows (Figure 5A; the recessive ms mutant is taken as an example): a homozygous ms mutant is used as female parent and crossed with hundreds of inbred lines with broad genetic backgrounds to get the heterozygous F1 hybrids. Then one of the F1 hybrids is self-pollinated to produce F2 seeds. Thereafter 50–100 of the F2 seeds from each cross are grown in various environments. The fertility segregation ratios

has many advantages such as the high germplasm utilization efficiency, higher male-sterility stability under various environments, and lower linkage rate with adverse traits. As more and more GMS genes have been cloned in crops, the BMS systems by using GMS gene have been developed in several crop plants and come into commercial utilization, such as SPT and MCS systems [3]. However, before utilization in the BMS systems, many characteristics of GMS gene and its mutant should be assessed systemically, such as genetic stability analysis of male-sterility,

in crop plants

Synthetic Biology - New Interdisciplinary Science

Figure 5.

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anther and pollen development in crop plants and have provided an important basis for developing BMS lines. Several attempts have been made to utilize GMS genes in combination with new technologies to achieve more feasible BMS systems in crop plants [3, 4, 6, 100]. Here, we introduce briefly the strategies, assessment, and applications of some typical BMS systems in crop plants (Table 2).

while the latter includes the RHS1 and RHS2 systems in maize and Barnase/Barstar

Molecular Cloning of Genic Male-Sterility Genes and Their Applications for Plant Heterosis…

The SPT system is one of the representatives of transgenic construct-driven nontransgenic seed systems initially developed in maize by using a transgenic maintainer strategy [62]. The SPT transgenic maintainer line is created by transforming the plant of interest with an SPT construct consisting of three components: (i) a wild-type male-fertility gene (e.g., Ms45) to restore fertility, (ii) a pollen lethality gene (e.g., ZmAA) to disrupt normal pollen development, and (iii) a fluorescent seed color marker gene (e.g., DsRed2) for seed sorting. Of the pollen grains produced by the SPT maintainer line, all have the ms45 genotype, 50% are nontransgenic, and 50% have the SPT transgenic elements. The latter grains are unable to germinate due to expression of the ZmAA gene. Thus, self-pollination of the SPT maintainer line produces both seeds with the same genotype of the SPT maintainer line (ms45/ms45 + SPT-T-DNA) and seeds with the male-sterile genotype (ms45/ ms45). The two types of seeds can be efficiently separated by mechanical color sorting, since the 50% of seeds contain the SPT elements showing a red color under green excitation light. When the male-sterile line (ms45/ms45) is pollinated with the SPT maintainer line, almost 100% of the resulting seeds have the ms45/ms45 genotype and can be used as male-sterile female lines for crossbreeding and hybrid seed

Since the maize SPT system was developed and applied successfully [62], several SPT-like systems have been developed in maize, rice, and wheat based on ZmMs44, OsNP1, and TaMs1 genes, respectively [22, 49, 69]. Although there are potentially many advantages of the SPT system, the rate of transgene transmission through pollen was found to vary with the highest rate being 0.518% [62]. Therefore, there is an increased risk of transgenic pollen flow during the male-sterile line propagation phase, thus resulting in greatly limited application in the countries and regions

To decrease the rate of transgene transmission through the pollen of SPT maintainer lines, our laboratory developed a MCS system by transforming a single MCS construct into the maize ms7, ms30, or ms33 mutant [9, 105, 106]. The MCS construct contains five functional modules: (i) a male-fertility gene (e.g., ZmMs7, ZmMs30 or ZmMs33) to restore fertility, (ii) two pollen disruption genes (e.g., ZmAA and Dam) to disrupt the production of transgenic pollen, (iii) a fluorescent color marker gene (e.g., DsRed2 or mCherry) for seed color sorting, and (iv) an herbicide-resistant gene (e.g., Bar) to prevent sophistication of seeds because it is beneficial for the propagation of high-purity MCS transgenic maintainer line seeds through herbicide spraying during specific stages of production. As the MCS construct harbors two pollen disruption modules, both of which can inhibit transgenic pollen formation or function, the transgene transmission rate through pollen is greatly decreased. Furthermore, the Bar gene in the MCS construct is helpful for propagating highly pure seeds of the transgenic maintainer line. Compared with the SPT construct, the MCS construct, which harbors two additional functional modules, the Bar and Dam genes, can produce maintainer and male-sterile lines with higher purity and greatly decrease the transgene transmission rate as well as the risk of transgene flow in commercial maize hybrid seed production. To promote commercial application, a field test of the MCS system in China is currently underway.

system in oilseed rape (Table 2).

production.

5.1.2 MCS System

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5.1.1 SPT- and SPT-like systems in crops

DOI: http://dx.doi.org/10.5772/intechopen.86976

with strict biotechnology regulatory oversight.
