The Arabidopsis BEL1-LIKE HOMEODOMAIN Proteins SAW1 and SAW2 Act Redundantly to Regulate KNOX Expression Spatially in Leaf Margins[W]

In Arabidopsis thaliana, the BEL1-like TALE homeodomain protein family consists of 13 members that form heterodimeric complexes with the Class 1 KNOX TALE homeodomain proteins, including SHOOTMERISTEMLESS (STM) and BREVIPEDICELLUS (BP). The BEL1-like protein BELLRINGER (BLR) functions together with STM and BP in the shoot apex to regulate meristem identity and function and to promote correct shoot architecture. We have characterized two additional BEL1-LIKE HOMEODOMAIN (BLH) proteins, SAWTOOTH1 (BLH2/SAW1) and SAWTOOTH2 (BLH4/SAW2) that, in contrast with BLR, are expressed in lateral organs and negatively regulate BP expression. saw1 and saw2 single mutants have no obvious phenotype, but the saw1 saw2 double mutant has increased leaf serrations and revolute margins, indicating that SAW1 and SAW2 act redundantly to limit leaf margin growth. Consistent with this hypothesis, overexpression of SAW1 suppresses overall growth of the plant shoot. BP is ectopically expressed in the leaf serrations of saw1 saw2 double mutants. Ectopic expression of Class 1 KNOX genes in leaves has been observed previously in loss-of-function mutants of ASYMMETRIC LEAVES (AS1). Overexpression of SAW1 in an as1 mutant suppresses the as1 leaf phenotype and reduces ectopic BP leaf expression. Taken together, our data suggest that BLH2/SAW1 and BLH4/SAW2 establish leaf shape by repressing growth in specific subdomains of the leaf at least in part by repressing expression of one or more of the KNOX genes

The Arabidopsis BELL1 and KNOX TALE Homeodomain Proteins Interact through a Domain Conserved between Plants and Animals

Interactions between TALE (three–amino acid loop extension) homeodomain proteins play important roles in the development of both fungi and animals. Although in plants, two different subclasses of TALE proteins include important developmental regulators, the existence of interactions between plant TALE proteins has remained unexplored. We have used the yeast two-hybrid system to demonstrate that the Arabidopsis BELL1 (BEL1) homeodomain protein can selectively heterodimerize with specific KNAT homeodomain proteins. Interaction is mediated by BEL1 sequences N terminal to the homeodomain and KNAT sequences including the MEINOX domain. These findings validate the hypothesis that the MEINOX domain has been conserved between plants and animals as an interaction domain for developmental regulators. In yeast, BEL1 and KNAT proteins can activate transcription only as a heterodimeric complex, suggesting a role for such complexes in planta. Finally, overlapping patterns of BEL1 and SHOOT MERISTEMLESS (STM) expression within the inflorescence meristem suggest a role for the BEL1–STM complex in maintaining the indeterminacy of the inflorescence meristem

Metabolic Engineering of Seeds Can Achieve Levels of ω-7 Fatty Acids Comparable with the Highest Levels Found in Natural Plant Sources1[OA]

Plant oils containing ω-7 fatty acids (FAs; palmitoleic 16:1Δ9 and cis-vaccenic 18:1Δ11) have potential as sustainable feedstocks for producing industrially important octene via metathesis chemistry. Engineering plants to produce seeds that accumulate high levels of any unusual FA has been an elusive goal. We achieved high levels of ω-7 FA accumulation by systematic metabolic engineering of Arabidopsis (Arabidopsis thaliana). A plastidial 16:0-ACP desaturase has been engineered to convert 16:0 to 16:1Δ9 with specificity >100-fold than that of naturally occurring paralogs, such as that from cat's claw vine (Doxantha unguis-cati). Expressing this engineered enzyme (Com25) in seeds increased ω-7 FA accumulation from <2% to 14%. Reducing competition for 16:0-ACP by down-regulating the β-ketoacyl-ACP synthase II 16:0 elongase further increased accumulation of ω-7 FA to 56%. The level of 16:0 exiting the plastid without desaturation also increased to 21%. Coexpression of a pair of fungal 16:0 desaturases in the cytosol reduced the 16:0 level to 11% and increased ω-7 FA to as much as 71%, equivalent to levels found in Doxantha seeds