Hairy Canola (Brasssica napus) re-visited: Down-regulating TTG1 in an AtGL3-enhanced hairy leaf background improves growth, leaf trichome coverage, and metabolite gene expression diversity

BMC Plant Biology

Research Article

Peta Bonham-Smith¹  Dwayne Hegedus²  Isobel Parkin²  Min Yu²  Margaret Y. Gruber²  Delwin Epp²  Naghabushana K. Nayidu³  Ushan I. Alahakoon⁴  Ali Taheri⁵ 

[1] Department of Biology, University of Saskatchewan, 112 Science Place, S7N5E2, Saskatoon, SK, Canada;Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, S7N0X2, Saskatoon, SK, Canada;Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, S7N0X2, Saskatoon, SK, Canada;Department of Biology, University of Saskatchewan, 112 Science Place, S7N5E2, Saskatoon, SK, Canada;Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, S7N0X2, Saskatoon, SK, Canada;Present address: DOW Agro-Sciences, 101-421 Downey Rd., S7N4L8, Saskatoon, SK, Canada;Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, S7N0X2, Saskatoon, SK, Canada;Present address: Department of Agriculture and Environmental Sciences, Tennessee State University, 3500 John A Merritt Blvd., 37209, Nashville, TN, USA;

关键词: Brassica napus;    GL3;    Trichome patterning and growth;    Broad metabolic gene expression changes;    Q-PCR and RNA sequencing;   

DOI  :  10.1186/s12870-015-0680-5

 received in 2014-12-19, accepted in 2015-12-11,  发布年份 2016

来源: Springer

【 摘 要 】

BackgroundThrough evolution, some plants have developed natural resistance to insects by having hairs (trichomes) on leaves and other tissues. The hairy trait has been neglected in Brassica breeding programs, which mainly focus on disease resistance, yield, and overall crop productivity. In Arabidopsis, a network of three classes of proteins consisting of TTG1 (a WD40 repeat protein), GL3 (a bHLH factor) and GL1 (a MYB transcription factor), activates trichome initiation and patterning. Introduction of a trichome regulatory gene AtGL3 from Arabidopsis into semi-glabrous Brassica napus resulted in hairy canola plants which showed tolerance to flea beetles and diamondback moths; however plant growth was negatively affected. In addition, the role of BnTTG1 transcription in the new germplasm was not understood.ResultsHere, we show that two ultra-hairy lines (K-5-8 and K-6-3) with BnTTG1 knock-down in the hairy AtGL3+ B. napus background showed stable enhancement of trichome coverage, density, and length and restored wild type growth similar to growth of the semi-glabrous Westar plant. In contrast, over-expression of BnTTG1 in the hairy AtGL3+ B. napus background gave consistently glabrous plants of very low fertility and poor stability, with only one glabrous plant (O-3-7) surviving to the T3 generation. Q-PCR trichome gene expression data in leaf samples combining several leaf stages for these lines suggested that BnGL2 controlled B. napus trichome length and out-growth and that strong BnTTG1 transcription together with strong GL3 expression inhibited this process. Weak expression of BnTRY in both glabrous and trichome-bearing leaves of B. napus in the latter Q-PCR experiment suggested that TRY may have functions other than as an inhibitor of trichome initiation in the Brassicas. A role for BnTTG1 in the lateral inhibition of trichome formation in neighbouring cells was also proposed for B. napus. RNA sequencing of first leaves identified a much larger array of genes with altered expression patterns in the K-5-8 line compared to the hairy AtGL3+B. napus background (relative to the Westar control plant). These genes particularly included transcription factors, protein degradation and modification genes, but also included pathways that coded for anthocyanins, flavonols, terpenes, glucosinolates, alkaloids, shikimates, cell wall biosynthesis, and hormones. A 2nd Q-PCR experiment was conducted on redox, cell wall carbohydrate, lignin, and trichome genes using young first leaves, including T4 O-3-7-5 plants that had partially reverted to yield two linked growth and trichome phenotypes. Most of the trichome genes tested showed to be consistant with leaf trichome phenotypes and with RNA sequencing data in three of the lines. Two redox genes showed highest overall expression in K-5-8 leaves and lowest in O-3-7-5 leaves, while one redox gene and three cell wall genes were consistently higher in the two less robust lines compared with the two robust lines.ConclusionThe data support the strong impact of BnTTG1 knockdown (in the presence of strong AtGL3 expression) at restoring growth, enhancing trichome coverage and length, and enhancing expression and diversity of growth, metabolic, and anti-oxidant genes important for stress tolerance and plant health in B. napus. Our data also suggests that the combination of strong (up-regulated) BnTTG1 expression in concert with strong AtGL3 expression is unstable and lethal to the plant.

【 授权许可】

CC BY   
© Alahakoon et al. 2016