GA2-oxidase氧化酶基因的研究进展

GA2-oxidase氧化酶(GA2ox)是影响赤霉素合成和代谢的关键酶之一,其可以将具有生物活性的赤霉素或前体分解成没有生物活性的物质,在植物的生长发育中起着重要的作用。目前已经在拟南芥、杨树、水稻和葡萄等多种植物中克隆表达,其功能在不同物种之间也存在着差异。本研究主要从GA2ox基因的表达模式和基因功能进行阐述,重点阐述了GA2ox基因的时空表达情况,环境和激素对GA2ox基因的表达影响;GA2ox基因对植物的株高、花、果实和种子性状的改变,及与抗性的相互作用,更好地为了解GA2ox基因的作用机制提供参考。

Activation of gibberellin 2-oxidase 6 decreases active gibberellin levels and creates a dominant semi-dwarf phenotype in rice (Oryza sativa L.)

Gibberellin （GA） 2-oxidase plays a key role in the GA catabolic pathway through 2β-hydroxylation.In the present study,we isolated a CaMV 35S-enhancer activation tagged mutant,H032.This mutant exhibited a dominant dwarf and GA-deficient phenotype,with a final stature that was less than half of its wild-type counterpart.The endogenous bioactive GAs are markedly decreased in the H032 mutant,and application of bioactive GAs （GA3 or GA4） can reverse the dwarf phenotype.The integrated T-DNA was detected 12.8 kb upstream of the OsGA2ox6 in the H032 genome by TAIL-PCR.An increased level of OsGA2ox6 mRNA was detected at a high level in the H032 mutant,which might be due to the enhancer role of the CaMV 35S promoter.RNAi and ectopic expression analysis of OsGA2ox6 indicated that the dwarf trait and the decreased levels of bioactive GAs in the H032 mutant were a result of the up-regulation of the OsGA2ox6 gene.BLASTP analysis revealed that OsGA2ox6 belongs to the class III of GA 2-oxidases,which is a novel type of GA2ox that uses C20-GAs （GA12 and/or GA53） as the substrates.Interestingly,we found that a GA biosynthesis inhibitor,paclobutrazol,positively regulated the OsGA2ox6 gene.Unlike the over-expression of OsGA2ox1,which led to a high rate of seed abortion,the H032 mutant retained normal flowering and seed production.These results indicate that OsGA2ox6 mainly affects plant stature,and the dominant dwarf trait of the H032 mutant can be used as an efficient dwarf resource in rice breeding.

The HB40-JUB1 transcriptional regulatory network controls gibberellin homeostasis in Arabidopsis

The gibberellins(GAs)are phytohormones that play fundamental roles in almost every aspect of plant growth and development.Although GA biosynthetic and signaling pathways are well understood,the mechanisms that control GA homeostasis remain largely unclear in plants.Here,we demonstrate that the homeobox transcription factor(TF)HB40 of the HD-Zip family regulates GA content at two additive con-trol levels in Arabidopsis thaliana.We show that HB40 expression is induced by GA and in turn reduces the levels of endogenous bioactive GAs by simultaneously reducing GA biosynthesis and increasing GA deac-tivation.Consistently,HB40 overexpression leads to typical GA-deficiency traits,such as small rosettes,reduced plant height,delayed flowering,and male sterility.By contrast,a loss-of-function hb40 mutation enhances GA-controlled growth.Genome-wide RNA sequencing combined with molecular-genetic ana-lyses revealed that HB40 directly activates the transcription of JUNGBRUNNEN1(JJUB1),a key TF that re-presses growth by suppressing GA biosynthesis and signaling.HB40 also activates genes encoding GA 2-oxidases(GA2oxs),which are major GA-catabolic enzymes.The effect of HB40 on plant growth is ultimately mediated through the induction of nuclear growth-repressing DELLA proteins.Collectively,our results reveal the important role of the HB40-JUB1 regulatory network in controlling GA homeostasis during plant growth.