Expression of GhNAC2 from G. herbaceum, improves root growth and imparts tolerance to drought in transgenic cotton and Arabidopsis.

NAC proteins are plant-specific transcription factors that play essential roles in regulating development and responses to abiotic and biotic stresses. We show that over-expression of the cotton GhNAC2 under the CaMV35S promoter increases root growth in both Arabidopsis and cotton under unstressed conditions. Transgenic Arabidopsis plants also show improved root growth in presence of mannitol and NaCl while transgenic cotton expressing GhNAC2 show reduced leaf abscission and wilting upon water stress compared to control plants. Transgenic Arabidopsis plants also have larger leaves, higher seed number and size under well watered conditions, reduced transpiration and higher relative leaf water content. Micro-array analysis of transgenic plants over-expressing GhNAC2 reveals activation of the ABA/JA pathways and a suppression of the ethylene pathway at several levels to reduce expression of ERF6/ERF1/WRKY33/ MPK3/MKK9/ACS6 and their targets. This probably suppresses the ethylene-mediated inhibition of organ expansion, leading to larger leaves, better root growth and higher yields under unstressed conditions. Suppression of the ethylene pathway and activation of the ABA/JA pathways also primes the plant for improved stress tolerance by reduction in transpiration, greater stomatal control and suppression of growth retarding factors.

Expression of an insecticidal fern protein in cotton protects against whitefly.

Whitefly (Bemisia tabaci) damages field crops by sucking sap and transmitting viral diseases. None of the insecticidal proteins used in genetically modified (GM) crop plants to date are effective against whitefly. We report the identification of a protein (Tma12) from an edible fern, Tectaria macrodonta (Fee) C. Chr., that is insecticidal to whitefly (median lethal concentration = 1.49 µg/ml in in vitro feeding assays) and interferes with its life cycle at sublethal doses. Transgenic cotton lines that express Tma12 at ∼0.01% of total soluble leaf protein were resistant to whitefly infestation in contained field trials, with no detectable yield penalty. The transgenic cotton lines were also protected from whitefly-borne cotton leaf curl viral disease. Rats fed Tma12 showed no detectable histological or biochemical changes, and this, together with the predicted absence of allergenic domains in Tma12, indicates that Tma12 might be well suited for deployment in GM crops to control whitefly and the viruses it carries.

Efficient production of gossypol from hairy root cultures of cotton (Gossypium hirsutum L.).

A protocol for induction and establishment of Agrobacterium rhizogenes mediated hairy root culture of Gossypium hirsutum was developed through infection with the A4 strain and co-cultivation on hormone-free semi-solid MS medium with B5 vitamins. It resulted in the emergence of hairy roots from the leaf explants, 21 days after infection. The transformation of hairy roots was established by PCR amplification of rol B and rol C genes of the Ri plasmid. All root lines expressed gossypol, although distinct inter-clonal quantitative variations were noticed. Five independent hairy root lines were studied for their growth kinetics as well as gossypol production. The yield potentials of one of them superseded others, as well as the non-transformed, in-vitro grown control roots. The content of gossypol in hairy roots reached a level of 2.43 mg/g DW. It was 4.5 times higher than in vitro and 1.47 times higher than in vivo grown roots of G. hirsutum. Selection of high gossypol producing hairy root lines of G. hirsutum can provide an alternative source for large-scale production of gossypol.