High levels of jasmonic acid antagonize the biosynthesis of gibberellins and inhibit the growth ofNicotiana attenuatastems

We show that Jasmonic acid antagonizes GA biosynthesis by strongly inhibiting the transcript accumulation of GA 20-OXIDASE and possibly GA 13-OXIDASE, the key genes in GA production, demonstrating that high JA levels antagonize GA biosynthesis in stems

Maria Heinrich; Christian Hettenhausen; Theo Lange; Hendrik W√ľnsche; Jingjing Fang; Ian T. Baldwin; Jianqiang Wu

2012

Scholarcy highlights

  • It has been shown that N. attenuata silenced in CDPK4 and CDPK5 has darker green leaves, highly decreased fertility, and stunted stem growth compared with WT
  • In this study we focused on a single line, irCDPK4/5-1, which was phenotypically indistinguishable from the other lines studied
  • To quantitatively examine plant growth, WT and irCDPK4/5 plants were grown concurrently under the glasshouse conditions optimized for N. attenuata and their growth parameters were measured over time
  • Consistent with the profile of Jasmonic acid content in stems over time, we found that the transcript levels of GA 20-OXIDASE were the most strongly suppressed in 48-day-old irCDPK4/5 plants, when they had the highest amount of JA in stems
  • Twenty-nine days after germination, when the stems of WT and irCDPK4/5 slightly elongated, no large differences were found between the lengths of WT and irCDPK4/5 stems; starting from 31 days after germination, stems of irCDPK4/5 appeared to be more than 50% shorter than those of WT plants
  • Using irCDPK4/5 plants, which were silenced in the JA suppressors, CDPK4 and CDPK5, and had dramatically increased levels of JA, we show that JA signaling represses the biosynthesis of GAs by inhibiting the transcription of several GA biosynthetic genes, including GA20ox, which encodes a key enzyme catalyzing the formation of bioactive GAs
  • The responsiveness of irCDPK4/5 to exogenously applied GA3 suggests that in N. attenuata Jasmonic acid may have no or only little inhibitory effect on GA signaling, and in contrast, probably due to the feedback regulatory pathway between GAs and the receptor GIBBERELLIN INSENSITIVE DWARF 1, the low GA contents in irCDPK4/5 induced more than a 10-fold increase in GID1b transcripts

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