The capacity of conventional breeding to simultaneously improve the yield and quality of cotton fiber is limited. The accumulation of the plant hormone indole-3-acetic acid (IAA) in cotton fiber initials prompted us to investigate the effects of genetically engineering increased IAA levels in the ovule epidermis. Targeted expression of the IAA biosynthetic gene iaaM, driven by the promoter of the petunia MADS box gene Floral Binding protein 7 (FBP7), increased IAA levels in the epidermis of cotton ovules at the fiber initiation stage. This substantially increased the number of lint fibers, an effect that was confirmed in a 4-year field trial. The lint percentage of the transgenic cotton, an important component of fiber yield, was consistently higher in our transgenic plants than in nontransgenic controls, resulting in a >15% increase in lint yield. Fiber fineness was also notably improved.

Members of the aquaporin (AQP) family have been suggested to transport aluminum (Al) in plants; however, the Al form transported by AQPs and the roles of AQPs in Al tolerance remain elusive. Here we report that NIP1;2, a plasma membrane-localized member of the Arabidopsis nodulin 26-like intrinsic protein (NIP) subfamily of the AQP family, facilitates Al-malate transport from the root cell wall into the root symplasm, with subsequent Al xylem loading and root-toshoot translocation, which are critical steps in an internal Al tolerance mechanism in Arabidopsis. We found that NIP1;2 transcripts are expressed mainly in the root tips, and that this expression is enhanced by Al but not by other metal stresses. Mutations in NIP1;2 lead to hyperaccumulation of toxic Al 3+ in the root cell wall, inhibition of root-to-shoot Al translocation, and a significant reduction in Al tolerance. NIP1;2 facilitates the transport of Al-malate, but not Al 3+ ions, in both yeast and Arabidopsis. We demonstrate that the formation of the Al-malate complex in the root tip apoplast is a prerequisite for NIP1;2-mediated Al removal from the root cell wall, and that this requires a functional root malate exudation system mediated by the Al-activated malate transporter, ALMT1. Taken together, these findings reveal a critical linkage between the previously identified Al exclusion mechanism based on root malate release and an internal Al tolerance mechanism identified here through the coordinated function of NIP1;2 and ALMT1, which is required for Al removal from the root cell wall, root-to-shoot Al translocation, and overall Al tolerance in Arabidopsis.aquaporin | nodulin 26-like protein | aluminum tolerance | organic acid exudation | malate

SummaryCotton (Gossypium hirsutum L.) fibers, one of the most important natural raw materials for textile industry, are highly elongated trichomes from epidermal cells of cotton ovules. DET2, an Arabidopsis steroid 5d-reductase, is considered to catalyze a major rate-limiting in brassinosteroid (BR) biosynthesis. To understand the role of BRs in cotton fiber development, GhDET2, which putatively encodes a steroid 5a-reductase by sequence comparison, was cloned from developing fiber cells. In vitro assessment of GhDET2 protein activity confirmed that GhDET2 encodes a functional steroid 5a-redutase. High levels of GhDET2 transcript were detected during the fiber initiation stage and the fiber rapid elongation stage. Antisense-mediated suppression of GhDET2 inhibited both fiber initiation and fiber elongation. Similarly, treating cultured ovules with finasteride, a steroid 5a-reductase inhibitor, reduced fiber elongation. Inhibition of fiber cell elongation by expression of antisense GhDET2 or the finasteride treatment could be reversed by epibrassinolide, a biologically active BR. Furthermore, seed coat-specific expression of GhDET2 increased fiber number and length. Therefore, GhDET2 and BRs play a crucial role in the initiation and elongation of cotton fiber cells, suggesting that modulation of BR biosynthesis factors may improve fiber quality or yield.

Entomopathogenic fungi are currently being used for the control of several insect pests as alternatives or supplements to chemical insecticides. Improvements in virulence and speed of kill can be achieved by understanding the mechanisms of fungal pathogenesis and genetically modifying targeted genes, thus improving the commercial efficacy of these biocontrol agents. Entomopathogenic fungi, such as Beauveria bassiana, penetrate the insect cuticle utilizing a plethora of hydrolytic enzymes, including chitinases, which are important virulence factors. Two chitinases (Bbchit1 and Bbchit2) have previously been characterized in B. bassiana, neither of which possesses chitin-binding domains. Here we report the construction and characterization of several B. bassiana hybrid chitinases where the chitinase Bbchit1 was fused to chitin-binding domains derived from plant, bacterial, or insect sources. A hybrid chitinase containing the chitin-binding domain (BmChBD) from the silkworm Bombyx mori chitinase fused to Bbchit1 showed the greatest ability to bind to chitin compared to other hybrid chitinases. This hybrid chitinase gene (Bbchit1-BmChBD) was then placed under the control of a fungal constitutive promoter (gpd-Bbchit1-BmChBD) and transformed into B. bassiana. Insect bioassays showed a 23% reduction in time to death in the transformant compared to the wild-type fungus. This transformant also showed greater virulence than another construct (gpd-Bbchit1) with the same constitutive promoter but lacking the chitin-binding domain. We utilized a strategy where genetic components of the host insect can be incorporated into the fungal pathogen in order to increase host cuticle penetration ability.