Vishnu Bhat

Somatic embryogenesis and regeneration of Cenchrus ciliaris genotypes from immature inflorescence explants

An efficient, highly reproducible system for plant regeneration via somatic embryogenesis was developed for Cenchrus ciliaris genotypes IG-3108 and IG-74. Explants such as seeds, shoot tip segments and immature inflorescences were cultured on Murashige and Skoog (MS) medium supplemented with 2.0–5.0 mg dm−3 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.5 mg dm−3 N6-benzyladenine (BA) for induction of callus. Callus could be successfully induced from all the three explants of both the genotypes. But the high frequency of embryogenic callus could be induced only from immature inflorescence explants. Somatic embryos were formed from nodular, hard and compact embryogenic calli when 2,4-D concentration was gradually reduced and BA concentration increased. Histological studies of somatic embryos indicated the presence of shoot apical meristem with leaf primordia. Ultrastructural details of globular and scutellar somatic embryos further validated successful induction and progression of somatic embryogenesis. Shoots were differentiated upon germination of somatic embryos on MS medium containing 2,4-D (0.25 mg dm−3) and BA or kinetin (1–5 mg dm−3). Roots were induced on ½ MS medium containing charcoal (0.8 %), and the regenerated plants transferred to pots and established in the soil showed normal growth and fertility.

Harnessing Apomixis for Heterosis Breeding in Crop Improvement

Apomixis is an asexual mode of reproduction through seeds where embryo develops without undergoing meiosis and fertilization of gametes. Majority of natural apomicts are polyploids and thought to have evolved through hybridization and polyploidization. Apomixis is highly desirable for agriculture as it fixes hybridity or heterosis. Apomicts form huge polyploid complexes in nature which are the results of their facultative nature. They harbor enormous amount of variability resulting in cytotypes. Majority of the crop plants do not reproduce through apomixis although few wild relatives of crop plants such as Pennisetum glaucum and Zea mays reproduce asexually. Harnessing apomixis for heterosis breeding of crop plants through introgression of this trait from tertiary to primary gene pool was not possible due to imprinting barriers. Deviation in endosperm balance number from the male and female parents during introgression caused poor seed set in Pennisetum and Zea mays hybrids. Apomicts exhibit three major developmental variations from normal sexual reproduction, viz. apomeiosis, parthenogenesis, and autonomous endosperm development. Initial studies indicated that all the three components are governed by a single or a few genes which was later refuted owing to recombinants showing independent events. Thus, genetics of apomixis is very complex and is often riddled with large-scale segregation distortions. In many apomictic grasses, transmission of apomixis is through a physically large, hemizygous, non-recombining genomic region. One of the genes from an apospory-specific genomic region (ASGR) of Pennisetum squamulatum, namely BABY BOOM LIKE, elicited parthenogenetic development of embryo in the sexual pearl millet. Unraveling of genetic and molecular mechanisms controlling apomixis could revolutionize the way agriculture is practiced.

Isolation, expression and evolution of FERTILIZATION INDEPENDENT ENDOSPERM homologs in Podostemaceae

Podostemaceae is an interesting family of angiosperms with unusual development and morphology. Among these, double fertilization, a defining feature of angiosperms is invariably missing in the family. Consequently, embryo development in the seeds takes place without endosperm. In recent years, the role of polycomb genes has garnered much interest because of their crucial role in seed development. Some of these genes have been reported from many unrelated species, underlining their high conservation. Thus, it becomes exciting to know the role of these genes in podostemads, which are devoid of double fertilization and endosperm. Here, we report the isolation, characterization and expression patterns of homologs of Fertilization Independent Endosperm (FIE) in two species of Podostemaceae, Zeylanidium olivaceum and Polypleurum stylosum. FIE like homologs could be identified in Z. olivaceum (ZoFIE) and P. stylosum (PsFIE). The predicted amino acid sequence of FIE homologs showed similarity to other homologs, containing the conserved seven WD40 repeats. Expression studies revealed that ZoFIE and PsFIE transcripts were present in the vegetative tissue (thallus in Podostemaceae) and the seedlings, similar to the model plants. However, the ZoFIE and PsFIE expression disappeared in the flowering stages. This unique pattern of expression suggests that in the absence of double fertilization and endosperm the expression of FIS complex genes perhaps is obliterated in Podostemaceae.

Genetic Fidelity of In Vitro Cultures of an Elite Indian Musa (Aa) Variety Matti

An efficient, simple, and rapid regeneration system for micro propagation of an elite Indian Banana variety Matti has been established. Shoot tip explants were regenerated on Murashige and Skoog (MS) medium supplemented with different concentrations of 6-benzylaminopurine (BAP) and Indole acetic acid (IAA). About 95% of the explants regenerated and produced on average about 28 shoots per explants, on mediumsupplemented with 100 μM of BAP. The hardening of the in vitrogrown plantlets showed almost 99% survivals upon transfer to soil in glass house conditions. Randomly amplified polymorphic DNA analysis of 10 randomly selected regenerated plants showed 100% uniformity and no detectable variation was observed.