Rht18 Semidwarfism in Wheat Is Due to Increased GA 2-oxidaseA9 Expression and Reduced GA Content.

Semidwarfing genes have improved crop yield by reducing height, improving lodging resistance, and allowing plants to allocate more assimilates to grain growth. In wheat (Triticum aestivum), the Rht18 semidwarfing gene was identified and deployed in durum wheat before it was transferred into bread wheat, where it was shown to have agronomic potential. Rht18, a dominant and gibberellin (GA) responsive mutant, is genetically and functionally distinct from the widely used GA-insensitive semidwarfing genes Rht-B1b and Rht-D1b In this study, the Rht18 gene was identified by mutagenizing the semidwarf durum cultivar Icaro (Rht18) and generating mutants with a range of tall phenotypes. Isolating and sequencing chromosome 6A of these "overgrowth" mutants showed that they contained independent mutations in the coding region of GA2oxA9GA2oxA9 is predicted to encode a GA 2-oxidase that metabolizes GA biosynthetic intermediates into inactive products, effectively reducing the amount of bioactive GA (GA1). Functional analysis of the GA2oxA9 protein demonstrated that GA2oxA9 converts the intermediate GA12 to the inactive metabolite GA110 Furthermore, Rht18 showed higher expression of GA2oxA9 and lower GA content compared with its tall parent. These data indicate that the increased expression of GA2oxA9 in Rht18 results in a reduction of both bioactive GA content and plant height. This study describes a height-reducing mechanism that can generate new genetic diversity for semidwarfism in wheat by combining increased expression with mutations of specific amino acid residues in GA2oxA9.

The fasciclin-like arabinogalactan protein family of Eucalyptus grandis contains members that impact wood biology and biomechanics.

Fasciclin-like arabinogalactan protein (FLA) families have been identified and characterised in key plant species, with some members exhibiting functional specialization. Here we identify the FLA family of Eucalyptus grandis, and investigate the roles of three single-FAS domain FLAs, with particular focus on secondary cell-wall formation and wood properties. We use various in-silico approaches to identify and characterise E. grandis genome FLAs, and perform phylogenetic comparisons with other species. For three key FLAs, we perform functional testing including promoter-reporter and overexpression transgenic approaches using eucalypts, poplar and tobacco. Of the 18 eucalypt FLAs identified, several were specifically and highly expressed in stems. The specificity to stem xylem vessel and fibre development was demonstrated with EniFLA1promoter:GUS studies in several species. Testing of select eucalypt FLAs resulted in altered wood development and properties, for example 35S:EgrFLA2 led to a 3 degree reduction in cellulose microfibril angle in eucalypt xylem fibres, and 35S:EgrFLA3 to a reduction in tobacco stem flexural strength. These results indicate that the eucalypt FLA family contains diverse members, and particular members with single FAS domains that are functionally specialized for secondary cell wall growth and properties.