Arabidopsis Pollen Fertility Requires the Transcription Factors CITF1 and SPL7 That Regulate Copper Delivery to Anthers and Jasmonic Acid Synthesis

Abstract

A deficiency of the micronutrient copper (Cu) leads to infertility and grain/seed yield reduction in plants. How Cu affects fertility, which reproductive structures require Cu, and which transcriptional networks coordinate Cu delivery to reproductive organs is poorly understood. Using RNA-seq analysis, we showed that the expression of a gene encoding a novel transcription factor, CITF1 (Cu-DEFICIENCY INDUCED TRANSCRIPTION FACTOR1), was strongly upregulated in Arabidopsis thaliana flowers subjected to Cu deficiency. We demonstrated that CITF1 regulates Cu uptake into roots and delivery to flowers and is required for normal plant growth under Cu deficiency. CITF1 acts together with a master regulator of copper homeostasis, SPL7 (SQUAMOSA PROMOTER BINDING PROTEIN LIKE7), and the function of both is required for Cu delivery to anthers and pollen fertility. We also found that Cu deficiency upregulates the expression of jasmonic acid (JA) biosynthetic genes in flowers and increases endogenous JA accumulation in leaves. These effects are controlled in part by CITF1 and SPL7. Finally, we show that JA regulates CITF1 expression and that the JA biosynthetic mutant lacking the CITF1-and SPL7-regulated genes, LOX3 and LOX4, is sensitive to Cu deficiency. Together, our data show that CITF1 and SPL7 regulate Cu uptake and delivery to anthers, thereby influencing fertility, and highlight the relationship between Cu homeostasis, CITF1, SPL7, and the JA metabolic pathway.

YSL3-mediated copper distribution is required for fertility, grain yield, and size in Brachypodium

“…Consistent with our past studies of copper distribution in the reproductive organs of A. 308 thaliana [6], the bulk of copper in florets of brachypodium was associated with anthers of 309 stamens and ovaries of pistils (Fig. 6C).…”

“…In this regard, it has been known for decades that the deficiency 54 for the micronutrient copper in alkaline, coarse-textured or organic soils that occupy more 55 than 30% of the world arable land, compromises crop fertility, reduces grain/seed yield and in 56 acute cases results in crop failure [2][3][4][5]. In accord with the essential role of copper in 57 reproduction, recent studies using synchrotron x-ray fluorescent (SXRF) microscopy 58 established that copper localizes to anthers and pistils of flowers in a model dicotyledonous 59 species, Arabidopsis thaliana, and failure to deliver copper to these reproductive organs 60 severely compromises fertility and seed set [6]. Although copper deficiency can be remedied 61 by the application of copper-based fertilizers, this approach is not environmentally friendly 62 and can lead to the build-up of toxic copper levels in soils [2,5,7].…”

“…Based on 69 studies in A. thaliana, copper uptake and internal distribution is mediated by CTR/COPT 70 transporters, P-type ATPases and members from the Yellow Stripe-Like (YSL) subfamily of 71 4 the oligopeptide (OPT) transporter family [7,[10][11][12][13][14][15][16][17]. The majority of these transporters are 72 transcriptionally upregulated by copper deficiency by a conserved transcription factor, SPL7 73 (Squamosa Promoter Binding Protein-like7), and a newly identified transcription factor 74 CITF1 (Copper-Deficiency Induced Transcription Factor1) [6, 18, 19].The expression of 75 several COPT family members is also induced in roots by the copper deficiency in Oryza 76 sativa and an emerging wheat model Brachypodium distachyon (from here on brachypodium), 77 and several brachypodium COPTs mediate low-affinity copper uptake [20, 21]. A member of 78 the YSL transporters, OsYSL16 functions in the phloem-based copper delivery to 79 reproductive organs in rice [22][23][24].…”

Do Arabidopsis Squamosa promoter binding Protein‐Like genes act together in plant acclimation to copper or zinc deficiency?

“…Moreover, spl1 spl7 spl12 did not differ from spl7 at seedling stage (Figure ). In comparison, a citf1 spl7 double mutant was seedling lethal unless the mutant was fertilized extensively with Cu (Yan et al., ). Furthermore, the comparison of internal Cu concentrations, of the Cu economy response and of mutant phenotypes at the reproductive stage led us to conclude that SPL1 and SPL12 have no, or only very small, autonomous roles in plant acclimation to Cu deficiency, different from SPL7 (Figures , Figures ).…”

Do Arabidopsis Squamosa promoter binding Protein-Like genes act together in plant acclimation to copper or zinc deficiency?

“…1). In comparison, a citf1 spl7 double mutant was seedling lethal unless the mutant was fertilized extensively with Cu (Yan et al 2017). Furthermore, the comparison of internal Cu concentrations, of the Cu economy response and of mutant phenotypes at the reproductive stage led us to conclude that SPL1 and SPL12 have no, or only very small, autonomous roles in plant acclimation to Cu deficiency, different from SPL7 (Figs.…”