Table 1 Heterologous functions of genes differentially expressed in Li ₂ WT and mutant fibers during elongation

Ghi.3835.2.S1_s_at

A. thaliana TRH1 (TINY ROOT HAIR 1). Functions as a potassium transporter and is required for the establishment of root tip growth. AT4G23640.

T-DNA insertion. Initiation sites for root hair growth are formed at trichoblasts but tip growth does not occur.

[68]

Ghi.8115.1.S1_s_at

G. hirsutum transcription factor GhMYB109. Fiber-specific R2R3 MYB transcription factor highly expressed during elongation.

Antisense suppression. Transgenic plants have impaired fiber initials that are smaller and shrunken compared to WT. Fiber elongation is inhibited in the transgenic plants. Mature fibers of transgenic plants have a short-fiber phenotype compared to WT with an ~33% reduction in fiber length.

[75, 76]

Ghi.8448.1.S1_x_at

G. hirsutum Beta tubulin1 (BTub1): family of small, globular proteins that form microtubules. Active component of the cytoskeleton.

Over-expression phenotype. Inducible expression in fission yeast resulted in longitudinal cell growth compared to un-induced cell and empty expression vector controls.

[77]

GhiAffx.24518.1.S1_s_at

A. thaliana BRASSINOSTEROID INSENSITIVE 1 (BRI1): Encodes a plasma membrane localized leucine-rich repeat receptor kinase involved in brassinosteroid signal transduction. AT4G39400.

EMS mutagenesis; T-DNA insertion. Short plant stature and small, dark green leaves. Shortened length of stem and pedicel epidermal cells. Reduced fertility. Reduced apical dominance. De-etiolation of dark-grown seedlings. Allelic bri1 mutants can be divided into severe, intermediate, and weak phenotypes.

[72, 86, 87]

GhiAffx.36984.1.S1_s_at

A. thaliana HERCULES1 (HERK1), a receptor kinase regulated by Brassinosteroids and required for cell elongation during vegetative growth. Functions redundantly with THESEUS1 (THE1). AT3G46290.

T-DNA insertion. Similar to WT in the herk1 mutant. In the herk1 the1 double mutant, petioles are reduced in length by half and petiole cells are shortened. Over-expression of HERK1 increased petiole length by 15-20%.

[66]

GhiAffx.47644.1.S1_at

A. thaliana HERCULES2 (HERK2), a receptor kinase regulated by Brassinosteroids and required for cell elongation during vegetative growth. Functions redundantly with HERCULES1 (HERK1) and THESEUS1 (THE1). AT1G30570.

T-DNA insertion. Similar to WT in the herk2 mutant. In the herk1 herk2 the1 triple mutant, petioles are further reduced in length compared to the herk1 the1 double mutant.

[67]

GhiAffx.62092.1.S1_at

A. thaliana XIK: Member of the type XI myosin protein family. Involved in root hair growth, trichome development, and organelle trafficking. AT5G20490.

T-DNA insertion. Normal root growth but root hairs are reduced in length by 50%. Leaf and stem trichomes have size and shape irregularities.

[69]

GhiAffx.6933.1.A1_at

A. thaliana CROOKED (CRK): Belongs to the DIS (distorted) gene family. Encodes an actin polymerization factor. Part of the Arpc2/3 protein complex as ARPC5. Involved in cell expansion of trichomes. AT4G01710.

EMS mutagenesis. Shortened leaf trichomes and trichome branches. Reduced polarized expansion of hypocotyls. Cells of expanding hypocotyls are shorter.

[70]

Gra.2039.1.S1_s_at

A. thaliana COBRA (COB): Glycosylphosphatidylinositol (GPI)-anchored protein localized primarily in the plasma membrane of the longitudinal sides of root cells. Necessary for oriented cell expansion in Arabidopsis. AT5G60920.

EMS mutagenesis; x-ray mutagenesis; T-DNA insertion. Increased root diameter and short roots due to increased width and reduced length of cells. Reduced root cell division rate and change in the orientation of root expansion.

[71, 88]

Gene more abundantly expressed in Li ₂ mutant fibers compared to WT fibers

Microarray Probesets ID

Sequence Description and Locus Tag

Mutant Phenotype

Reference

Ghi.7529.1.A1_s_at; Ghi7529.1.S1_s_at; Gra.511.1.A1_s_at

A. thaliana AHP1 (HISTIDINE-CONTAINING PHOSPHOTRANSMITTER 1): AHPs function as redundant positive regulators of cytokinin signaling. AT3G21510.

T-DNA insertion. Loss of root elongation sensitivity in response to exogenous application of cytokinin.

[80]

GhiAffx.12783.1.S1_s_at

A. thaliana homeobox protein HAT22: member of the HD-Zip II family of transcription factors. AT4G37790.

Mutant phenotype not described. Up-regulated in response to exogenous cytokinin application in A. thaliana WT and cytokinin-deficient mutant plants

[81]

Ghi.3235.1.A1_at

A. thaliana UDP-glucosyl transferase 73C2 (UGT73C2): Involved in cytokinin N-glucosylation. Along with UGT73C1, glucosylates all cytokinins at the N7 and N9 positions. AT2G36760.

Over-expression phenotype. Plants constitutively over-expressing UGT73C1 were generated, but no phenotype was reported.

[82]

Ghi.9236.1.S1_at

A. thaliana UDP-glycosyltransferase 73C5 (UGT73C5)/DON-GLUCOSYLTRANSFERASE 1 (DOGT1): Glucosylates brassinolide and castasterone in the 23-O position. Presumably involved in the homeostasis of those steroid hormones and regulation of BR activity. Also shown to glucosylate the OH group on the N6-side chain of the cytokinins trans-zeatin and dihydrozeatin. AT2G36800.

Over-expression phenotype. Plants over-expressing UGT73C5/DOGT1 displayed typical BR-deficient dwarf phenotypes such as reduced hypocotyl elongation, and contained reduced levels of BRs.

[82, 83]

Ghi.4551.1.S1_at

A. thaliana SUPPRESSOR OF BIR1 (SOBIR1): Encodes a leucine rich repeat transmembrane protein that is a receptor-like kinase (RLK). SOBIR1 is suggested to be a critical positive regulator of cell death. AT2G31880.

Over-expression phenotype. Constitutive over-expression of sobir1 results in activation of cell death.

[89]