Serendipita indica promotes P acquisition and growth in tea seedlings under P deficit conditions by increasing cytokinins and indoleacetic acid and phosphate transporter gene expression

Abstract

The culturable endophytic fungus <i>Serendipita indica</i> has many beneficial effects on plants, but whether and how it affects physiological activities and phosphorus (P) acquisition of tea seedlings at low P levels is unclear. The objective of this study was to analyze the effects of inoculation with <i>S</i>. <i>indica</i> on growth, gas exchange, chlorophyll fluorescence, auxins, cytokinins, P levels, and expressions of two phosphate transporter (<i>PT</i>) genes in leaves of tea (<i>Camellia sinensis</i> L. cv. Fudingdabaicha) seedlings grown at 0.5 μM (P_0.5) and 50 μM (P₅₀) P levels. Sixteen weeks after the inoculation, <i>S</i>. <i>indica</i> colonized roots of tea seedlings, with root fungal colonization rates reaching 62.18% and 81.34% at P_0.5 and P₅₀ levels, respectively. Although plant growth behavior, leaf gas exchange, chlorophyll values, nitrogen balance index, and chlorophyll fluorescence parameters of tea seedlings were suppressed at P_0.5 versus P₅₀ levels, inoculation of <i>S</i>. <i>indica</i> mitigated the negative effects to some extent, along with more prominent promotion at P_0.5 levels. <i>S</i>. <i>indica</i> inoculation significantly increased leaf P and indoleacetic acid concentrations at P_0.5 and P₅₀ levels and leaf isopentenyladenine, dihydrozeatin, and transzeatin concentrations at P_0.5 levels, coupled with the reduction of indolebutyric acid at P₅₀ levels. Inoculation of <i>S</i>. <i>indica</i> up-regulated the relative expression of leaf <i>CsPT1</i> at P_0.5 and P₅₀ levels and <i>CsPT4</i> at P_0.5 levels. It is concluded that <i>S</i>. <i>indica</i> promoted P acquisition and growth in tea seedlings under P deficit conditions by increasing cytokinins and indoleacetic acid and <i>CsPT1</i> and <i>CsPT4</i> expression.