Engineering of gibberellin levels in citrus by sense and antisense

Abstract

http://jxb.oxfordjournals.org/Carrizo citrange (Citrus sinensis x Poncirus trifoliata) is a citrus hybrid 4 widely used as a rootstock, whose genetic manipulation to improve 5 different growth characteristics is of high agronomic interest. In this work 6 we have produced transgenic Carrizo citrange plants overexpressing 7 sense and antisense CcGA20ox1 (a key enzyme of GA biosynthesis) 8 under control of the 35S promoter to modify plant architecture. As 9 expected, taller (sense) and shorter (antisense) phenotype correlated with 10 higher and lower levels, respectively, of active GA1 in growing shoots. In 11 contrast, other phenotypic characteristics seemed to be specific of citrus, 12 or different to those described for similar transgenics in other species. For 13 instance thorns, typical organs of citrus at juvenile stages, were much 14 longer in sense and shorter in antisense plants, and xylem tissue was 15 reduced in leaf and internode of sense plants. Antisense plants presented 16 a bushy phenotype, suggesting a possible effect of GAs on auxin 17 biosynthesis and/or transport. The main foliole of sense plants was longer, 18 although total leaf area was reduced. Leaf thickness was smaller in sense 19 and bigger in antisense plants due to changes in the spongy parenchyma. 20 Internode cell length was not altered in transgenic plants, indicating that in 21 citrus GAs regulate cell division rather than cell elongation. Interestingly, 22 the described phenotypes were not apparent when transgenic plants were 23 grafted on non-transgenic rootstock. This suggests that roots contribute to 24 the GA economy of aerial parts in citrus and opens the possibility of using 25 the antisense plants as dwarfing rootstocks.We thank J.A. Pina for technical assistance, and Dr. E. Carbonell and J. 34 Pérez for statistical analyses. This research was supported in part by grants CICYT AGL2003-01644, 1 INIA RTA04-13 and BIO2003-00151. C. 2 Fagoaga was recipient of an INIA-CCAA postdoctoral contract. I. Lliso was 3 recipient of an IVIA predoctoral fellowship. D.J. Iglesias and F.R. Tadeo 4 were recipients of INIA-CCAA and “Ramón y Cajal” MEC postdoctoral 5 contracts, respectively. 6 7Peer reviewe