An invasive weed-associated bacteria confers enhanced heat stress tolerance in wheat.

Global temperatures are expected to increase due to climate change, and heat stress is one of the major limiting factors affecting future agriculture. To identify plant-associated microorganisms which can promote heat stress tolerance in wheat, we have screened several bacteria isolated from etiolated seedlings of the invasive noxious weed Parthenium hysterophorus. One isolate designated as Ph-04 was found to confer enhanced heat stress tolerance in wheat. The 16S rRNA gene sequence analysis showed that Ph-04 isolate shared highest sequence identity with Bacillus paramycoides species of the Bacillus cereus group. Ph-04 treated wheat seeds exhibited enhanced germination, longer coleoptile, radicle and seminal root length than control seedlings when grown in the dark at optimum and high temperatures. Similarly, under autotrophic conditions, Ph-04 treated plants also exhibited enhanced heat stress tolerance with a significant increase in membrane integrity and significantly reduced levels of H2O2 under heat stress compared to control plants. This observed heat stress tolerance is associated with constitutively higher basal levels of proline, and activity of antioxidant enzymes, catalase (CAT) and ascorbate peroxidase (APX) in Ph-04 treated plants grown under unstressed conditions with further increase under heat stress conditions compared to controls. Plant recovery after heat stress also showed that the Ph-04 treated plants exhibited significantly less damage in terms of survival percentage and exhibited better morphological and physiological characteristics compared to control plants. The study proves that invasive weeds can harbour potentially beneficial microorganisms, which can be transferred to non-native crop (host) plants to improve climate resilience characteristics.

A mitogen-activated protein kinase gene, AhMPK3 of peanut: molecular cloning, genomic organization, and heterologous expression conferring resistance against Spodoptera litura in tobacco.

Mitogen-activated protein kinase cascade plays a very important role in plant signal transduction mechanism. A full length cDNA of 1,514 bp length, corresponding to a mitogen-activated protein kinase gene was cloned from peanut (Arachis hypogaea). Based on its high homology with Arabidopsis AtMPK3, the cDNA was designated as AhMPK3. It carried an open reading frame of 1,113 bp encoding a 371 amino acid polypeptide. AhMPK3 bears TEY motif in its activation loop and belongs to the A1 subgroup of MAPK family. Southern blot analysis revealed that AhMPK3 exists in two copies in peanut genome and its structural organization revealed well-conserved nature of these signaling components across different species. AhMPK3 when transiently expressed in tobacco leaves was found to localize in both nucleus and cytoplasm. Transgenic tobacco plants ectopically expressing AhMPK3 exhibited enhanced resistance to first and second instar larvae of Spodoptera litura and constitutively higher transcript levels of defense response genes like PR1a, PR1b, LOX1, PI-II etc. Apart from this when wounded, transgenic plants accumulated high levels of PI-II and PR1b transcripts rapidly compared to wild type indicating the occurrence of a priming phenomenon.

Constitutive expression of a trypsin protease inhibitor confers multiple stress tolerance in transgenic tobacco.

Protease inhibitors have been reported to confer insect resistance in transgenic plants, except for a rice protease inhibitor that conferred drought tolerance in transgenic rice plants. We have cloned a protease inhibitor of tobacco that is expressed under treatment with ABA, hydrogen peroxide, methyl jasmonate and wounding. The cDNA codes for a six-domain serine protease inhibitor with a deduced sequence of 396 amino acids. We have generated transgenic tobacco plants expressing the protease inhibitor constitutively under the 35S promoter. When analyzed in the T(2) generation, these transgenic plants exhibited tolerance to sodium chloride, variable pH and sorbitol, together with the expected resistance to the insect pests Spodoptera litura and Helicoverpa armigera. The transgenic plants showed enhanced seed germination, root length and root-shoot ratio, significantly enhanced total chlorophyll content and reduced thiobarbituric acid-reactive substances under stress. Under sodium chloride treatment, the transgenic plants have enhanced protease inhibitor activity. The transgenic plants exhibited a higher potassium content and an optimum Na+/K+ ratio. To our knowledge, this is the first report of transgenic plants with constitutive protease inhibitor expression showing tolerance to a wide range variable pH in the culture medium along with other stresses.

Constitutive expression of Arabidopsis NPR1 confers enhanced resistance to the early instars of Spodoptera litura in transgenic tobacco.

In Arabidopsis, NPR1 (AtNPR1) regulates salicylic acid (SA)-mediated activation of PR genes at the onset of systemic acquired resistance. AtNPR1 also modulates SA-induced suppression of jasmonic acid-responsive gene expression, and npr1 mutants manifest enhanced herbivore resistance. We have raised stable transgenic tobacco lines, expressing AtNPR1 constitutively, which showed elevated expression of PR1 and PR2 genes upon SA treatment. Herbivore bioassays with a generalist polyphagous pest, Spodoptera litura, revealed that the transgenic lines exhibited enhanced resistance compared to the wild-type plants, particularly with respect to younger larval populations. Insect-mediated injury induced several protease inhibitors (PIs), more significantly a 40-kDa serine PI in all the tobacco lines, but the induction was higher in the transgenic plants. We show in this communication that heterologous expression of AtNPR1 provides enhanced resistance to early larval populations of the herbivore, Spodoptera in transgenic tobacco plants.