Transformation and evaluation of Broad-Spectrum insect and weedicide resistant genes in Gossypium arboreum (Desi Cotton)

Categories of resistance in cotton genotypes, Gossypium spp. against cotton-melon aphid, Aphis gossypii (Hemiptera: Aphididae)

Cotton-melon aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is emerging as a potential threat to cotton cultivation worldwide. The resistance categories in Gossypium arboreum to A. gossypii still need to be explored. We screened 87 G. arboreum and 20 Gossypium hirsutum genotypes against aphids under natural field conditions. Twenty-six selected genotypes from these 2 species were tested under glasshouse conditions for resistance categories (antixenosis, antibiosis, and tolerance). Resistance categories were assessed by no-choice antibiosis assay, free-choice aphid settling assay, cumulative aphid days using population buildup tests, chlorophyl loss index, and damage ratings. No-choice antibiosis experiment revealed that the G. arboreum genotypes GAM156, PA785, CNA1008, DSV1202, FDX235, AKA2009-6, DAS1032, DHH05-1, GAM532, and GAM216 had a significant adverse effect on aphid development time, longevity, and fecundity. Gossypium arboreum genotypes CISA111 and AKA2008-7 expressed a low level of antixenosis but possessed antibiosis and tolerance. Aphid resistance persisted uniformly at different plant developmental stages studied. The chlorophyl loss percentage and damage rating scores were lower in G. arboreum than in G. hirsutum genotypes, indicating the existence of tolerance in G. arboreum to aphids. Logical relations analysis of resistance contributing factors depicted the presence of antixenosis, antibiosis, and tolerance in the G. arboreum genotypes PA785, CNA1008, DSV1202, and FDX235, indicating their utility for evaluating the mechanisms of resistance and aphid resistance introgression breeding into G. hirsutum to develop commercially cultivated cotton lines.

Efficient genotype-independent cotton genetic transformation and genome editing

Cotton (Gossypium spp.) is one of the most important fiber crops worldwide. In the last two decades, transgenesis and genome editing have played important roles in cotton improvement. However, genotype dependence is one of the key bottlenecks in generating transgenic and gene-edited cotton plants through either particle bombardment or Agrobacterium-mediated transformation. Here, we developed a shoot apical meristem (SAM) cell-mediated transformation system (SAMT) that allowed the transformation of recalcitrant cotton genotypes including widely grown upland cotton (Gossypium hirsutum), Sea island cotton (Gossypium barbadense), and Asiatic cotton (Gossypium arboreum). Through SAMT, we successfully introduced two foreign genes, GFP and RUBY, into SAM cells of some recalcitrant cotton genotypes. Within 2-3 months, transgenic adventitious shoots generated from the axillary meristem zone could be recovered and grown into whole cotton plants. The GFP fluorescent signal and betalain accumulation could be observed in various tissues in GFP- and RUBY-positive plants, as well as in their progenies, indicating that the transgenes were stably integrated into the genome and transmitted to the next generation. Furthermore, using SAMT, we successfully generated edited cotton plants with inheritable targeted mutagenesis in the GhPGF and GhRCD1 genes through CRISPR/Cas9-mediated genome editing. In summary, the established SAMT transformation system here in this study bypasses the embryogenesis process during tissue culture in a conventional transformation procedure and significantly accelerates the generation of transgenic and gene-edited plants for genetic improvement of recalcitrant cotton varieties.

Heterologous expression of cry1Ia12 insecticidal gene in cotton encodes resistance against pink bollworm, Pectinophora gossypiella (Lepidoptera: Gelechiidae); an alternate insecticidal gene for insect pest management

BACKGROUND

Cotton is continuously exposed to sucking and chewing insect pest pressure since emergence to harvesting. Pink bollworm (Pectinophora gossypiella) has become major chewing insect pest to reduce the cotton yield and results in bad lint quality even in transgenic crops. The efficiency of insecticidal genes has been compromised due to extensive utilization of transgenic crops.

METHODS AND RESULTS

The present study was conducted to evaluate the efficacy of an alternate cry1Ia12 insecticidal gene against pink bollworm (PBW) in cotton. Agrobacterium tumefaciens strain LBA4404 harboring pCAMBIA2300 expression vector containing cry1Ia12 gene under the control of 35S CaMV was used to transform a local cotton cultivar GS-01. The various molecular analyses revealed the transgene integration and expression in primary transformants. Among five selected transgenic plants, tcL-08 showed maximum (16.06-fold) mRNA expression of cry1Ia12 gene whereas tcL-03 showed minimum (2.33-fold) expression. Feeding bioassays of 2nd and 3rd instar pink bollworm (PBW) larvae on immature cotton bolls, flowers and cotton squares revealed up to 33.33% mortality on tcL-08 while lowest mortality (13.33%) was observed in tcL-03 and tcL-15. Furthermore, the average weight and size of survived larvae fed on transgenic plants was significantly lesser than the average weight of larvae survived on non-transgenic plants.

CONCLUSIONS

The present study suggests the cry1Ia12 gene as an alternate insecticidal gene for the resistance management of cotton bollworms, especially PBW.

Enhancing the resilience of transgenic cotton for insect resistance

BACKGROUND

The efficacy of Bt crystal proteins has been compromised due to their extensive utilization in the field. The second-generation Bt vegetative insecticidal proteins could be the best-suited alternative to combat resistance build-up due to their broad range affinity with midgut receptors of insects.

MATERIAL AND RESULTS

The codon-optimized synthetic vegetative insecticidal proteins (Vip3Aa) gene under the control of CaMV35S promoter was transformed into a locally developed transgenic cotton variety (CKC-01) expressing cry1Ac and cry2A genes. Transformation efficiency of 1.63% was recorded. The highest Vip3Aa expression (51.98-fold) was found in MS3 transgenic cotton plant. Maximum Vip3Aa protein concentration (4.23 µg/mL) was calculated in transgenic cotton plant MS3 through ELISA. The transgenic cotton plant (MS3) showed one copy number on both chromatids in the homozygous form at chromosome 8 at the telophase stage. Almost 99% mortality of H. armigera was recorded in transgenic cotton plants expressing double crystal proteins pyramided with Vip3Aa gene as contrasted to transgenic cotton plant expressing only double crystal protein with 70% mortality.

CONCLUSIONS

The results obtained during this study suggest that the combination of Bt cry1Ac, cry2A, and Vip3Aa toxins is the best possible alternative approach to combat chewing insects.