K. A. Geetha

Characterization, genetic improvement and cultivation of Chlorophytum borivilianum —an important medicinal plant of India

Chlorophytum borivilianum is an important medicinal plant known as ‘Safed musli’, used in many Ayurvedic vital tonics and aphrodisiac formulations. The species was first described from India in 1954 and reached rare status in nature due to overexploitation. Owing to its increased demand, the species has attracted the attention of farmers as well as researchers in several institutions. The present paper deals with various research aspects such as conservation biology, cytology, chemistry, plant genetic resources, micropropagation, crop management, etc. conducted on the crop for the last two decades in India. The species is diploid 2 n =4 x =28 and is mainly vegetatively propagated. Seeds remain dormant for nearly 10 months and also suffer from poor germination. Fleshy roots of the species contain saponins having therapeutic value. Germplasm collections made from different states in India show the occurrence of wide genetic variability in terms of plant type, maturity period, growth and yield characters, and size and shape of fleshy roots. Although the species is cross-pollinated in nature, self-pollination is also feasible artificially. One high-yielding cultivar and two high-yielding morphotypes have been recently identified. A micropropagation protocol using different explants has been standardized and agrotechnology for cultivation developed. Successful use of synthetic seed has also been reported. The article presents a comprehensive overview of the current state of research in the species with due emphasis on future thrust and possibilities.

Characterization of mode of reproduction in Commiphora wightii [(Arnot) Bhandari] reveals novel pollen–pistil interaction and occurrence of obligate sexual female plants

Guggul [Commiphora wightii (Arnot) Bhandari], a polygamous woody tree valued for its medicinal oleoresin gum rich in guggulsterone, is reported to reproduce via sporophytic apomixis. Details about its natural diversity, and mode and extent of sexual reproduction are, however, scanty. Therefore, a comprehensive investigation of guggul reproduction was made employing histology, controlled pollination, flow cytometry and RAPD analyses of progeny to assess the occurrence and extent of sexual reproduction. We report the discovery of obligate sexual female plants of guggul through these studies. Also, we document a unique pollen–pistil incompatibility that prevents all but one pollen tube growth into the style to effect fertilization. Consequently, obligate sexual female plants produced single-seeded fruit although each flower contains four ovules. In apomictic plants bearing more than one seed per fruit, at most only one seed was of sexual origin. Further, flow cytometric analysis conclusively demonstrated that endosperm development occurs either autonomously or following triple fusion. Autonomous endosperm development was invariably associated with endoreduplication, a unique feature of apomixis in guggul. Despite predominance of apomixis, a low frequency of sexual reproduction was found to persist in apomictic plants yielding new genetic variation. RAPD analysis clearly distinguished accessions and was useful in identifying sexual progenies. The implications of the novel pollen–pistil interaction on establishment and spread of apomixis in guggul are discussed. The study has not only revealed novel features of guggul reproduction but also opened new opportunities for molecular genetic analysis of sporophytic apomixis and breeding improvement of guggul.

Brassica juncea Lines with Substituted Chimeric GFP-CENH3 Give Haploid and Aneuploid Progenies on Crossing with Other Lines

Haploids and doubled haploids are invaluable for basic genetic studies and in crop improvement. A novel method of haploid induction through genetic engineering of the Centromere Histone Protein gene, CENH3, has been demonstrated in Arabidopsis. The present study was undertaken to develop haploid inducer (HI) lines of Brassica juncea based on the principles elaborated in Arabidopsis. B. juncea was found to carry three copies of CENH3 which generated five different transcripts, of which three transcripts resulted from alternative splicing. Unlike Arabidopsis thaliana where native CENH3 gene was knocked out for constructing HI lines, we used RNAi approach to knockdown the native CENH3 genes. Further, to rescue CENH3 silenced cells, a GFP-CENH3-tailswap construct having N terminal GFP fused to H3.3 tail sequences and synthetic CENH3 histone fold domain sequences was devised. A total 38 transgenic B. juncea plants were regenerated following co-transformation with both silencing and rescue cassettes and transgenics carrying either or both the constructs were obtained. Transgenic status was confirmed through PCR, Southern and qRT-PCR analyses. Co-transformed lines were crossed to untransformed B. juncea or a line expressing only GFP-tailswap. FACS and cytological analyses of progenies revealed partial or complete elimination of B. juncea chromosomes thereby giving rise to aneuploids and haploid. This is the first report in a polyploid crop demonstrating that CENH3 engineering could be used to develop HI lines.