Abstract
Trichome formation in Arabidopsis is regulated by several key regulators, and plants hormones such as gibberellin, salicylic acid, jasmonic acid and cytokinins have been shown to regulate trichome formation by affecting the transcription or activities of the key regulators. We report here the identification of two abscisic acid (ABA) responsive genes, SMALLER TRICHOMES WITH VARIABLE BRANCHES (SVB) and SVB2 as trichome formation regulator genes in Arabidopsis. The expression levels of SVB and SVB2 were increased in response to ABA treatment, their expression levels were reduced in the ABA biosynthesis mutant aba1-5, and they have similar expression pattern. In addition to the trichome defects reported previously for the svb single mutant, we found that even though the trichome numbers were largely unaffected in both the svb and svb2 single mutants generate by using CRISPR/Cas9 gene editing, the trichome numbers were greatly reduced in the svb svb2 double mutants. On the other hand, trichome numbers were increased in SVB or SVB2 overexpression plants. RT-PCR results show that the expression of the trichome formation key regulator gene ENHANCER OF GLABRA3 (EGL3) was affected in the svb svb2 double mutants. Our results suggest that SVB and SVB2 are ABA responsive genes, and SVB and SVB2 function redundantly to regulate trichome formation in Arabidopsis.
Highlights
Trichomes are developed from epidermal cells on the surface of the plant aerial parts, and they can protect plants from some of the biotic and abiotic stresses such as excessive heat, water loss, and insect or pathogen attacks, due to their ability to increase thickness of the boundary layer between epidermal surface and environment [1,2].As a good model for studying cell fate determination, trichome formation in Arabidopsis has been extensively studied
We further examined the expression of SMALLER TRICHOMES WITH VARIABLE BRANCHES (SVB) in seedlings of the abscisic acid (ABA) biosynthesis mutant aba1-5 [51], and found that the expression level of SVB was decreased in the aba1-5 mutant when compared with that in the Ler wild type (Figure 1b)
To examine how SVB and SVB2 may regulate trichome formation, we examined the expression of trichome formation key regulator genes in the svb svb2 double mutants, we found that the expression of ENHANCER OF GLABRA3 (EGL3) was increased when compared with that in the Col wild type seedlings (Figure 6d)
Summary
Trichomes are developed from epidermal cells on the surface of the plant aerial parts, and they can protect plants from some of the biotic and abiotic stresses such as excessive heat, water loss, and insect or pathogen attacks, due to their ability to increase thickness of the boundary layer between epidermal surface and environment [1,2].As a good model for studying cell fate determination, trichome formation in Arabidopsis has been extensively studied. Accumulated evidence suggests that the key regulators of trichome formation in Arabidopsis are a few transcription factors [3,4,5,6,7] These transcription factors including the WD40-repeat protein TRANSPARENT TESTA GLABRA1 (TTG1) [8], the R2R3 MYB transcription factor GLABRA1 (GL1) [9], the bHLH transcription factor GLABRA3 (GL3) or ENHANCER OF GLABRA3 (EGL3) [10,11], the homeodomain protein GLABRA2 (GL2) [12], and the R3 MYB transcription factors including TRYPTICHON (TRY), CAPRICE (CPC), ENHANCER OF TRY AND CPC1 (ETC1), ETC1, ETC3, TRICHOMELESS1 (TCL1) and TCL2 [13,14,15,16,17,18,19,20,21]. These R3 MYB proteins including ETC2, TCL1 and TCL2 can move to the neighboring cells, where they compete with GL1 for binding GL3, blocking the formation of the MBW complex, resulting in the inhibition of trichome formation [3,4,5,6,7,22,23,24]
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