IPT9, a cis-zeatin cytokinin biosynthesis gene, promotes root growth

Abstract

Cytokinin and auxin are plant hormones that coordinate many aspects of plant development. Their interactions in plant underground growth are well established, occurring at the levels of metabolism, signaling, and transport. Unlike many plant hormone classes, cytokinins are represented by more than one active molecule. Multiple mutant lines, blocking specific parts of cytokinin biosynthetic pathways, have enabled research in plants with deficiencies in specific cytokinin-types. While most of these mutants have confirmed the impeding effect of cytokinin on root growth, the ipt29 double mutant instead surprisingly exhibits reduced primary root length compared to the wild type. This mutant is impaired in cis-zeatin (cZ) production, a cytokinin-type that had been considered inactive in the past. Here we have further investigated the intriguing ipt29 root phenotype, opposite to known cytokinin functions, and the (bio)activity of cZ. Our data suggest that despite the ipt29 short-root phenotype, cZ application has a negative impact on primary root growth and can activate a cytokinin response in the stele. Grafting experiments revealed that the root phenotype of ipt29 depends mainly on local signaling which does not relate directly to cytokinin levels. Notably, ipt29 displayed increased auxin levels in the root tissue. Moreover, analyses of the differential contributions of ipt2 and ipt9 to the ipt29 short-root phenotype demonstrated that, despite its deficiency on cZ levels, ipt2 does not show any root phenotype or auxin homeostasis variation, while ipt9 mutants were indistinguishable from ipt29. We conclude that IPT9 functions may go beyond cZ biosynthesis, directly or indirectly, implicating effects on auxin homeostasis and therefore influencing plant growth.

Identification and Expression Analysis of the Isopentenyl Transferase (IPT) Gene Family under Lack of Nitrogen Stress in Oilseed (Brassica napus L.)

“…It suggested that oilseed rape may be able to maintain its growth by altering expression levels of BnIPTs in R in response to adverse external environments. Most of the IPT mutants of Arabidopsis have confirmed the existence of an inhibitory effect of CKs on root growth [55]; however, overexpression of IPT in plants could promote the translocation of CKs bottom-up and delay leaf senescence: overexpression of tomato IPTs under a root-specific promoter resulted in a slight increase the concentration of endogenous CKs in the plant, but the proportion of CKs derivatives in the root was significantly altered, resulting in biosynthesis and metabolism to be altered; while leaf senescence of tomatoes was regulated by the CK-mediated root-shoot pathway, and CK-mediated signals were transferred from xylem to leaves, thus altering the level of CKs biosynthesis in leaves and delaying leaf senescence [56].…”

Metabolic profiling reveals key metabolites regulating adventitious root formation in ancient Platycladus orientalis cuttings

“…The contents of 5′-methylthioadenosine, cis -zeatin- O -glucoside, and adenine in zeatin biosynthesis gradually increased after wounding ( Figure 7A ). Thus, wounding reactivated and promoted cell division, which regulated the differentiation and growth of various cells ( Antoniadi et al., 2022 ; Sun et al., 2023 ). Metabolites, such as l -glutamine, l -histidine, l -isoleucine, l -leucine, and l -arginine, are involved in aminoacyl-tRNA biosynthesis and are sources of carbon skeleton for basic metabolite synthesis on wounding response ( Figure 7B ) ( Guan et al., 2021 ).…”

“…Similar to the results of metabolic pathways in cuttings after the rejuvenation of walnut, the contents of zeatin, amino acid synthetics, and other substances in the callus increased after wounding, which provided a basis for cell differentiation and growth ( Song et al., 2021 ). Zeatin is an important hormone controlling plant growth and development, in which 5′-methylthioadenosine (MTA) is a key metabolite of the Met cycle ( Jin et al., 2013 ; Antoniadi et al., 2022 ). For instance, MTA nucleosidase activity was the highest during the fruit development period of Lycopersicon esculentum ( Kushad et al., 1985 ).…”

Physiological Mechanism through Which Al Toxicity Inhibits Peanut Root Growth

“…Isopentenyltransferases (IPTs) are pivotal enzymes that catalyze cytokinin biosynthesis, while IAA influences Zeatin biosynthesis by regulating IPT expression [ 67 ]. Studies have demonstrated that Arabidopsis AtIPT9 stimulates cytokinin synthesis and enhances root growth [ 68 ]. In the current study, the zeatin level in the roots of peanuts was significantly reduced under Al poisoning.…”