<i>ZmCCD10a</i> Encodes a Distinct Type of Carotenoid Cleavage Dioxygenase and Enhances Plant Tolerance to Low Phosphate

Abstract

Carotenoid cleavage dioxygenases (CCDs) drive carotenoid catabolism to produce various apocarotenoids and immediate derivatives with particular developmental, ecological, and agricultural importance. How <i>CCD</i> genes evolved with species diversification and the resulting functional novelties in cereal crops have remained largely elusive. We constructed a unified four-clade phylogenetic tree of <i>CCD</i>s, revealing a previously unanchored basal clade <i>CCD10</i> <i>CCD10</i> underwent highly dynamic duplication or loss events, even in the grass family. Different from cleavage sites of CCD8 and ZAXINONE SYNTHASE (ZAS), maize (<i>Zea mays</i>) ZmCCD10a cleaved differentially structured carotenoids at 5, 6 (5', 6') and 9, 10 (9', 10') positions, generating C₈ (6-methyl-5-hepten-2-one) and C₁₃ (geranylacetone, α-ionone, and β-ionone) apocarotenoids in <i>Escherichia coli</i> Localized in plastids, ZmCCD10a cleaved neoxanthin, violaxanthin, antheraxathin, lutein, zeaxanthin, and β-carotene in planta, corroborating functional divergence of ZmCCD10a and ZAS. <i>ZmCCD10a</i> expression was dramatically stimulated in maize and teosinte (<i>Z. mays</i> ssp. <i>parviglumis</i>, <i>Z. mays</i> ssp. <i>huehuetenangensis</i>, <i>Zea luxurians</i>, and <i>Zea diploperennis</i>) roots by phosphate (Pi) limitation. <i>ZmCCD10a</i> silencing favored phosphorus retention in the root and reduced phosphorus and biomass accumulation in the shoot under low Pi. Overexpression of <i>ZmCCD10a</i> in Arabidopsis (<i>Arabidopsis thaliana</i>) enhanced plant tolerance to Pi limitation by preferential phosphorus allocation to the shoot. Thus, <i>ZmCCD10a</i> encodes a unique CCD facilitating plant tolerance to Pi limitation. Additionally, <i>ZmCCD10a</i> silencing and overexpression led to coherent alterations in expression of <i>PHOSPHATE STARVATION RESPONSE REGULATOR 1</i> (<i>PHR1</i>) and Pi transporters, and cis-regulation of <i>ZmCCD10a</i> expression by ZmPHR1;1 and ZmPHR1;2 implies a probable <i>ZmCCD10a</i>-involved regulatory pathway that adjusts Pi allocation.