Abstract
AbstractAgrobacterium-mediated transient expression (TE) is an important tool in plant genetics study and biotechnology. Citrus is one of the top tree crops, butAgrobacterium-mediated TE remains problematic in citrus. Previous study has shown that pretreatment of citrus leaves withXanthomonas citrisubsp.citri(Xcc), which causes citrus canker in almost all citrus cultivars, significantly improves the TE efficacy. Here we have shown thatXccpromotesAgrobacterium-mediated TE via improvingAgrobacteriumgrowth, suppressing plant immune response, triggering cell division, and upregulating plant cell wall degrading enzymes. We demonstrate thatXccpromotesAgrobacterium-mediated TE via PthA and mutation ofpthA4abolishes the promoting effect ofXcc.PthA4 is known to trigger cell division of citrus. We have demonstrated the causative relationship between cell division andAgrobacterium-mediated TE using cell division inhibitor mimosine. Importantly, the differential effects of mimosine and colchicine onXccpromotingAgrobacterium-mediated TE indicate that S-phase is critical for agroinfiltration of citrus tissues. In addition, PthA4 is known to upregulate plant growth hormones auxin (IAA), gibberellin and cytokinin, as well as cell degrading enzymes (e.g., cellulase). Exogenous application of IAA, cytokinin, and cellulase but not gibberellin significantly improvedAgrobacterium-mediated TE in leaves of sweet orange, pummelo, Meiwa kumquat, lucky bamboo and rose mallow. Our study provides a mechanistic understanding regarding howXccpromotesAgrobacterium-mediated TE and identified two practical measures to improveAgrobacterium-mediated TE via pretreatment with plant hormones (i.e., auxin and cytokinin) and cellulase.
Publisher
Cold Spring Harbor Laboratory