AUTHOR=Du Junbo , Jiang Hengke , Sun Xin , Li Yan , Liu Yi , Sun Mengyuan , Fan Zhou , Cao Qiulin , Feng Lingyang , Shang Jing , Shu Kai , Liu Jiang , Yang Feng , Liu Weiguo , Yong Taiwen , Wang Xiaochun , Yuan Shu , Yu Liang , Liu Chunyan , Yang Wenyu 

TITLE=Auxin and Gibberellins Are Required for the Receptor-Like Kinase ERECTA Regulated Hypocotyl Elongation in Shade Avoidance in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00124

DOI=10.3389/fpls.2018.00124

ISSN=1664-462X

ABSTRACT=<p>Plants use shade avoidance strategy to escape the canopy shade when grown under natural conditions. Previous studies showed that the Arabidopsis receptor-like kinase ERECTA (ER) is involved in shade avoidance syndrome. However, the mechanisms of ER in modulating SAR by promoting hypocotyl elongation are unknown yet. Here, we report that ER regulated hypocotyl elongation in shade avoidance requires auxin and gibberellins (GAs). The T-DNA insertional <italic>ER</italic> mutant <italic>er-3</italic> shows a less hypocotyl length than that in Col-0 wild type. Promoter::GUS staining analysis shows that <italic>ER</italic> and its paralogous genes <italic>ERECTA-LIKE1</italic> (<italic>ERL1</italic>) and <italic>ERECTA-LIKE2</italic> (<italic>ERL2</italic>) are differentially expressed in the seedlings, of which only <italic>ER</italic> is most obviously upregulated in the hypocotyl by shade treatment. Exogenous feeding assay by using media-application with vertical-grown of Arabidopsis seedlings showed that the hypocotyl length of <italic>er-3</italic> is partially promoted by indol-3-acetic acid (IAA), while it is relatively insensitive of <italic>er-3</italic> to various concentrations of IAA than that of Col-0. Hypocotyl elongation of <italic>er-3</italic> is promoted similar to that of Col-0 by high temperature in the white light condition, but the elongation was not significantly affected by the treatment of the auxin transport inhibitor 1-<italic>N</italic>-naphthylphthalamic acid (NPA). Exogenous GA3 increased the hypocotyl elongation of both <italic>er-3</italic> and the wild type in the shade condition, and the GA3 biosynthesis inhibitor paclobutrazol (PAC) severely inhibits the hypocotyl elongation of Col-0 and <italic>er-3</italic>. Further analysis showed that auxin biosynthesis inhibitors yucasin and <sc>L</sc>-kynurenine remarkably inhibited the hypocotyl elongation of <italic>er-3</italic> while yucasin shows a more severe inhibition to <italic>er-3</italic> than Col-0. Relative expression of genes regulating auxin homeostasis and signaling, and GA homeostasis is less in <italic>er-3</italic> than that in Col-0. Furthermore, genetic evidences show that <italic>ER</italic> regulated hypocotyl elongation is dependent of PHYTOCHROME B (PHYB). Overall, we propose that ER regulated shade avoidance by promoting hypocotyl elongation is PHYB-dependent and requires auxin and GAs.</p>