Over-expression of a pepper plastid lipid-associated protein in tobacco leads to changes in plastid ultrastructure and plant development upon stress

Proteins homologous to fibrillin, a pepper plastid lipid-associated protein involved in carotenoid storage in fruit chromoplasts, have been recently i dentified in leaf chloroplasts from several species and shown to be induced upon environmental stress. To further investigate the role of the protein, transgenic Nicotiana tabacum plants over-expressing fibrillin using a cons titutive promoter were generated. Transgenics grown under standard light in tensities (300 mu mol photons m(-2) sec(-1)) were found to contain substant ial amounts of fibrillin in flowers and leaves. in leaves, the protein was immunolocalized within chloroplasts in both stromal and thylakoid subfracti ons. No change was noticed in thylakoid structures from transgenics, but ch loroplasts contained an increased number of plastoglobules organized in clu sters. In petals, leucoplasts were also found to contain more agglutinated plastoglobutes. The effects of environmental factors on fibrillin gene expr ession and protein localization were studied in tobacco leaves. Less fibril lin was present in plants grown under low light intensities, which can be e xplained by the involvement of a light-dependent splicing step in the contr ol of fibrillin gene expression in leaves. Analysis of protein subfractions from plants subjected to drought or high light showed that both stresses r esulted in fibrillin association with thylakoids. Whereas no growth differe nce between wildtype (WT) and transgenic plants was noticed under low light conditions, transgenics exhibit a longer main stem, enhanced development o f lateral stems and accelerated floral development under higher light inten sities. These data suggest that fibrillin-related proteins fulfil an import ant function in plant development in relation to environmental constraints.