Overexpression of GhKTI12 Enhances Seed Yield and Biomass Production in Nicotiana Tabacum

Abstract

Crop molecular breeding primarily focuses on increasing the trait of plant yield. An elongator-associated protein, <i>KTI12</i>, is closely associated with plant biomass and yield. <i>KTI12</i> is involved in developmental processes of most organs, including the leaf, root, flower, and seed, through regulating cell division and differentiation. Previous work has shown that in upland cotton (<i>Gossypium hirsutum</i>), <i>GhKTI12</i> regulates plant height, flowering, and tolerance to salt and drought stress. However, little is known about the molecular regulation mechanism of <i>GhKTI12</i> in plant developmental processes. In this study, we identified the main <i>GhKTI12</i> (<i>Gh_D02G144400</i>) gene and transformed it into tobacco (<i>Nicotonia tabacum</i> cv NC89). From seven transgenic lines, we obtained three (OE5, OE6 and OE8) with high expression of <i>GhKTI12</i>; compared with wild type plants, these three lines exhibited larger plant size, later flowering, and higher seed yield. Microscopic observation revealed that the number of leaf epidermal cells and stem parenchyma cells was increased by ~55%. Biochemical analysis showed that chlorophyll content and starch accumulation were significantly increased in younger leaves at the top canopy of transgenic plants, which may contribute to improved photosynthetic rate and, in turn, increased seed yield. To understand the molecular mechanism of <i>GhKTI12</i> in transgenic plants development, two lines (OE6 and OE8) with higher expression levels of <i>GhKTI12</i> were used as representative plants to conduct RNA-seq analysis. Through transcriptome analysis of the plant's shoot apical meristematic tissue of these two lines, we identified 518 upregulated genes and 406 downregulated genes common to both overexpression lines. A large number of cellular component genes associated with cell division and differentiation, such as <i>RD21</i>, <i>TET8</i>, <i>KTN80</i>, <i>AOX1</i>, <i>AOX2</i>, <i>CP1</i>, and <i>KIC</i>, were found to be upregulated, and genes showing the most downregulation included MADS-box genes related to flowering time, such as <i>MADS6</i>, <i>AP1</i>, <i>AP3</i>, <i>AGL8</i>, <i>AGL6</i>, <i>SEP1</i>, and <i>SEP2</i>. Downregulation of these genes caused delayed flowering time and longer vegetative stage during development. Combined with the upregulation of the yield-related gene <i>RD21</i>, the <i>GhKTI12</i> transgenic plants could produce a higher seed yield. We here show that the overexpression of <i>GhKTI12</i> could positively improve key agronomic traits in tobacco by regulating cell proliferation, photosynthesis, and organ development, and suggest that homologs of <i>GhKTI12</i> may also be important in the genetic improvement of other crop plants.