The Genetic Complexity of Type-IV Trichome Development Reveals the Steps towards an Insect-Resistant Tomato.

The leaves of the wild tomato Solanumgalapagense harbor type-IV glandular trichomes (GT) that produce high levels of acylsugars (AS), conferring insect resistance. Conversely, domesticated tomatoes (S. lycopersicum) lack type-IV trichomes on the leaves of mature plants, preventing high AS production, thus rendering the plants more vulnerable to insect predation. We hypothesized that cultivated tomatoes engineered to harbor type-IV trichomes on the leaves of adult plants could be insect-resistant. We introgressed the genetic determinants controlling type-IV trichome development from S.galapagense into cv. Micro-Tom (MT) and created a line named "Galapagos-enhanced trichomes" (MT-Get). Mapping-by-sequencing revealed that five chromosomal regions of S. galapagense were present in MT-Get. Further genetic mapping showed that S. galapagense alleles in chromosomes 1, 2, and 3 were sufficient for the presence of type-IV trichomes on adult organs but at lower densities. Metabolic and gene expression analyses demonstrated that type-IV trichome density was not accompanied by the AS production and exudation in MT-Get. Although the plants produce a significant amount of acylsugars, those are still not enough to make them resistant to whiteflies. We demonstrate that type-IV glandular trichome development is insufficient for high AS accumulation. The results from our study provided additional insights into the steps necessary for breeding an insect-resistant tomato.

Analysis of NAC Domain Transcription Factor Genes of Tectona grandis L.f. Involved in Secondary Cell Wall Deposition.

NAC proteins are one of the largest families of plant-specific transcription factors (TFs). They regulate diverse complex biological processes, including secondary xylem differentiation and wood formation. Recent genomic and transcriptomic studies of Tectona grandis L.f. (teak), one of the most valuable hardwood trees in the world, have allowed identification and analysis of developmental genes. In the present work, T. grandis NAC genes were identified and analyzed regarding to their evolution and expression profile during wood formation. We analyzed the recently published T. grandis genome, and identified 130 NAC proteins that are coded by 107 gene loci. These proteins were classified into 23 clades of the NAC family, together with Populus, Eucalyptus, and Arabidopsis. Data on transcript expression revealed specific temporal and spatial expression patterns for the majority of teak NAC genes. RT-PCR indicated expression of VND genes (Tg11g04450-VND2 and Tg15g08390-VND4) related to secondary cell wall formation in xylem vessels of 16-year-old juvenile trees. Our findings open a way to further understanding of NAC transcription factor genes in T. grandis wood biosynthesis, while they are potentially useful for future studies aiming to improve biomass and wood quality using biotechnological approaches.

Novel natural genetic variation controlling the competence to form adventitious roots and shoots from the tomato wild relative Solanum pennellii.

Tomato (Solanum lycopersicum L.) is an attractive model to study the genetic basis of adventitious organ formation capacity, since there is considerable natural genetic variation among wild relatives. Using a set of 46 introgression lines (ILs), each containing a small chromosomal segment of Solanum pennellii LA716 introgressed and mapped into the tomato cultivar M82, we characterized a high shoot-regeneration capacity for ILs 3-2, 6-1, 7-1, 7-2, 8-2, 8-3, 9-1, 9-2, 10-2 and 10-3, when cotyledon explants were cultivated on medium containing 5.0µM BAP. F1 seedlings from the crosses 'Micro-Tom×ILs' and 'ILs×ILs' demonstrated that the shoot regeneration capacity of most ILs was dominant and that the regeneration ability of IL8-3 enhanced that of the other ILs in an additive manner. The ILs 3-2, 7-1, 8-3, and 10-2 also exhibited enhanced root formation on MS medium containing 0.4µM NAA, indicating that these chromosomal segments may contain genes controlling the competence to assume distinct cell fates, rather than the induction of a specific organ. We also performed the introgression of the genes controlling competence into the model system 'Micro-Tom'. The further isolation of such genes will improve our understanding of the molecular basis of organogenic capacity.