Transgenic Citrus Expressing an Arabidopsis NPR1 Gene Exhibit Enhanced Resistance against Huanglongbing (HLB; Citrus Greening)

Commercial sweet orange cultivars lack resistance to Huanglongbing (HLB), a serious phloem limited bacterial disease that is usually fatal. In order to develop sustained disease resistance to HLB, transgenic sweet orange cultivars ‘Hamlin’ and ‘Valencia’ expressing an Arabidopsis thaliana NPR1 gene under the control of a constitutive CaMV 35S promoter or a phloem specific Arabidopsis SUC2 (AtSUC2) promoter were produced. Overexpression of AtNPR1 resulted in trees with normal phenotypes that exhibited enhanced resistance to HLB. Phloem specific expression of NPR1 was equally effective for enhancing disease resistance. Transgenic trees exhibited reduced diseased severity and a few lines remained disease-free even after 36 months of planting in a high-disease pressure field site. Expression of the NPR1 gene induced expression of several native genes involved in the plant defense signaling pathways. The AtNPR1 gene being plant derived can serve as a component for the development of an all plant T-DNA derived consumer friendly GM tree.     

Molecular Evolution of the Cottoid Fish Endemic to Lake Baikal Deduced from Nuclear DNA Evidence

Lake Baikal in Eastern Siberia contains a remarkable flock of 29 species of teleost fishes of the suborder Cottoidei (sculpins, bullheads) that are endemic to the lake and its associated rivers and occupy all depth habitats down to over 1500 m. The species are divided into three families, the Cottidae with 7 species, the Abyssocottidae with 20 species, and the Comephoridae with 2 species. Nucleotide sequences of the rod opsin gene from 12 of these species, plus a non-Baikal marine species, have been used to examine the evolutionary relations and the divergence time of the flock. Phylogenetic trees, generated by neighbor-joining and maximum parsimony, indicate that the unique Comephoridae family with its viviparity and unusual appearance is closely related to the Cottidae and Abyssocottidae, whereas the genusCottocomephorus,at present placed in the Cottidae, was the first to diverge from the ancestral species and forms a separate lineage. The major adaptation to deep water would appear to be of relatively recent origin, and there is evidence that the ancestral species occupied a shallow-water marine or brackish habitat. Estimates of antiquity obtained from synonymous substitutions place the origin of the species flock at around 4.9 million years ago.