SATrends Issue 83
October 2007
1. A master switch to tackle drought stress
A cDNA profile obtained from the leaf samples of transgenic groundnut expressing rd29A::DREB1A during day 2 to 6 of the dry down cycle. Arrows indicate the differentially expressed cDNAs in transgenic plant, when compared with non-transgenic plant. Straight arrows indicate newly expressed, and downward arrows indicate down regulated cDNAs.

In SATrends issues 62 (Jan 2006) and 75 (Feb 2007), we reported that when the DREB1A gene driven by the promoter of a stress-inducible gene, rd29A, was genetically introduced into groundnuts, it not only improved the transpiration efficiency, but also induced a positive root response under water stress conditions. Here we report that the expression of DREB1A transcription factor also manifests in a differential gene expression under drought stress, thereby, acting as a master switch to counter the effects of drought.

The total RNA from the leaves of five selected transgenic events expressing the DREB1A gene under stress were subjected to differential display of transcripts for comparing the expression profiles of transgenic and wild type groundnut plants under water stress. This enabled the detection of gene transcripts that were expressed in response to the stress. A total of 51 differentially expressed transcripts were identified, where 35 transcripts were newly expressed, 11 were up-regulated, and five were down-regulated. Analysis of the partial sequences of 40 cDNAs indicated that most were from abiotic stress responsive genes (SRGs) that could be classified broadly in four groups as follows:

Nevertheless, only 17 cDNA clones showed a strong similarity with the published ESTs, thereby indicating that a majority of these may be novel. This would indicate that the expression of DREB1A in transgenic plants might influence the expression of these genes either directly or indirectly. Further analysis of the transcript levels may provide insights into the regulatory pathways of these genes.

Analysis of the newly expressed genes indicate that their products might function co-operatively to protect the cells from dehydration and may also play an important role in plant adaptive mechanisms under water stress conditions. Cloning and characterization of full-length cDNAs and promoter regions of the genomic sequences corresponding to the stress-regulated clones could provide further insights into the mechanism of expression of an individual gene, as well as its potential role in stress response. Future activities would involve the identification and functional analysis of these transcripts for use in both genetic engineering as well as marker-assisted selection for plant breeding.

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2. Spotlight on hybrid seed production

Seven years ago ICRISAT and the Institute d’Economie Rural (IER) in Mali started developing the first Guinea-race male-sterile female parent lines of sorghum. Since then, new hybrid sorghums based on Guinea-race germplasm are being developed to achieve higher grain productivity while maintaining the grain quality and adaptive traits of the Guinea-race sorghums primarily grown by farmers in West Africa. Hybrids produced on these female parents have now been tested in multi-location and multi-year trials. Results show that these new hybrids provide a 31% yield increase over the best local variety, averaged over all hybrids and environments in these trials. The promise shown by these hybrids has led to the expansion of this research with the involvement of National Research Programs in Burkina Faso (INERA), Niger (INRAN), Nigeria (IAR), Senegal (ISRA), and Ghana (SARI).

Sorghum Breeder F Rattunde in the seed production field with private and public seed producers.

However, even the most outstanding hybrid will not bring benefits to sorghum producers and consumers without effective seed production and marketing. It is in this context that we in the research community are working simultaneously on hybrid seed production techniques as well as identifying commercially viable hybrids. The first large scale seed production fields in 2005 showed that photoperiod sensitive Guinea-race parents of nearly identical maturity could produce one ton/ha hybrid seed at a 1:1 female to male ratio. Thus even higher seed yields should be possible with an increased female to male ratio. Further testing of off-season hybrid seed production and seed production trials with parents of differing photoperiod sensitivities are continuing at ICRISAT-Samanko. The two replicate trials involve multiple dates of sowing, alternative fertilization methods to maximize nicking between parents, and increased female to male ratios.

Two Hybrid Seed Production field visits were conducted to coincide with flowering in these Hybrid Sorghum Seed Production plots at ICRISAT-Samanko in 2007. The seed production methods currently under test were first presented to the Farmer Cooperative Seed Association (COPROSEM), the supporting NGO, ACOD, and the Umbrella Farmer Organization (AOPP) by IER and ICRISAT. The second field visit brought together directors of emerging private seed enterprises and representatives of the National Seed Service, AOPP, and the coordinator for a new Foundation Seed Unit in the Malian IER Research Institute. These events definitely raised awareness of advances in both hybrid development and hybrid seed production methods for West Africa, and provide a basis for continued interaction and collaboration to make commercial sorghum hybrids for Sudanian West Africa a reality in the near future.

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