Cytoplasmic male sterility in plants.pptx

Dr.S.KARTHIKUMAR
Associate Professor
Department of Biotechnology
Kamaraj College of Engineering and Technology, K.Vellakulam-625701, TN, India
Email: [email protected]

1. Cytoplasmic male sterility in plants

2. Male sterility is the failure of plants to produce functional pollen or male gametes. Male sterility is more prevalent than female sterility. The reason is that the male sporophyte and gametophyte are less protected from the environment than the ovule and embryo sac. Male sterility can arise spontaneously via  mutations  in nuclear genes and/or cytoplasmic or cytoplasmic–genetic. Male-sterile plants can set seed and propagate. Female-sterile plants cannot develop seeds and will not propagate. Male sterility

3. Cytoplasmic male sterility CMS refers to the condition under which a plant is unable to produce functional pollen, and is widespread among higher plants. Cytoplasmic male sterility is under extranuclear genetic control (mitochondrial or plastid genomes). It shows  non-Mendelian inheritance , with male sterility inherited maternally. Generally, there are two types of cytoplasm, i.e. Normal and Sterile cytoplasms . These types exhibit reciprocal differences. Plasmogenes – Cytoplasmic male sterility (CMS) is governed by plasmogenes located in the mt-DNA, which causes pollen abortion in higher plants. CMS can arise spontaneously in breeding lines, as a result of wide crosses or the interspecific exchange of nuclear and cytoplasmic genomes, or following mutagenesis

4. Cytoplasmic-genetic male sterility & Fertility Restoration As CMS is controlled by an extranuclear genome, nuclear genes may have the capability to restore fertility. When nuclear restoration of fertility genes is available for a CMS system in any crop, it is cytoplasmic–genetic male sterility. So, the sterility is manifested by the influence of both nuclear and cytoplasmic genes. In cytoplasmic–genetic male sterility restoration of fertility is done using  restorer lines  carrying nuclear genes. The male-sterile line is maintained by crossing with a  maintainer line  carrying the same nuclear genome but with normal fertile cytoplasm. Rf  genes – In many cases, it has been found that male fertility can be restored by nuclear-encoded fertility restorer ( Rf ) gene. On the one hand, sterility results from mitochondrial genes causing cytoplasmic dysfunction, and on the other, fertility restoration relies on nuclear genes that suppress cytoplasmic dysfunction. Therefore CMS/ Rf  systems also matter in the study of interactions between nuclear and mitochondrial genomes. The  Rf  genes have no expression of their own unless the sterile cytoplasm is present.  Rf  genes are required to restore fertility in sterile cytoplasm that causes sterility.

5. the failure of plants to produce functional anthers, pollen, or male gametes ( Rick 1944) 1763--Kölreuter observed anther abortion in some plant species and some inter-specific hybrids (Darwin, 1876) the first male sterility system was developed in onion in 1943 (Jones, 1943) The CMS in carrot by Welch and Grimball (1947) Induced CMS in pearl millet by Ethidium bromide (Burton and hanna , 1976) More prevalent than female sterility: Male sporophyte and gametophyte less protected from environment than ovule and embryo sac. Easy to detect male sterility, because a large number of pollen for study available. Easy to assay male sterility: staining technique ( caramine , lactophenol or iodine) Mariani et al., 1990 Male sterility

6. When two selected – inbreeding lines are crossed, resulting F1 hybrids are more robust and produce high yield of harvest than parent plants. Since, according to Mendelian law, offspring of F2 is heterogenous. Most of F2 plant have some homozygosity resulting in yield depression. If --- F1 hybrid can’t be further propagated, then yield will be higher But, each year the farmer has to purchase new hybrid seed from seed companies.

7. CAUSES OF MALE STERILITY Absence or malformation of male organs (stamens) in bisexual plants or no male flowers in dioecious plants Failure to develop normal anther Abnormal pollen maturation; inability to germinate on compatible stigma Non dehiscent anthers but viable pollen Barriers other than incompatibility preventing pollen from reaching ovule ( Kaul ,1988)

8. Classification of male sterility ( Kaul , 1988)

9. Importance of CMS Hybrid seed production-  CMS is useful in hybrid seed production of several important crop species like maize, sorghum, pearl millet, rice, wheat, pigeonpea and a number of vegetable crops where it eliminates the process of  hand emasculation . CMS is an important part of hybrid maize The first commercial cytoplasmic male sterile, discovered in Texas, is known as CMS-T. The use of CMS-T eliminated the need for  detasseling .

10. Molecular  Basis of CMS Most types of CMS are caused by the expression of aberrant  chimeric genes  locating in mitochondrial genomes. Chimeric genes,  literally a mutated gene, form through the combination of portions of two or more coding sequences to produce new genes which merge whole gene sequences into a single reading frame and often retain their original functions.  A number of CMS-determining genes  have been identified. These include the T-urf13 gene in T-cytoplasm Maize, Pcf in  Petunia,  orf138 and orf224 in  Brassica,  and orf79 and orfH79 in Rice. These genes are unusual open reading frames (ORFs) that have resulted from mitochondrial DNA rearrangements. In many cases, male fertility of CMS plants can be overcome by certain nuclear-encoded gene(s) called restorer-of-fertility (Rf). Nuclear restorer ( Rf  or  Fr ) genes function to suppress the deleterious effects of CMS-associated mitochondrial abnormalities by diverse mechanisms. This interaction results in a new sterility type called  Cytoplasmic Genetic Male Sterility .