Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
PLoS Genet. 2012 Feb;8(2):e1002506. doi: 10.1371/journal.pgen.1002506. Epub 2012 Feb 9.
For self-pollinating plants to reproduce, male and female organ development must be coordinated as flowers mature. The Arabidopsis transcription factors AUXIN RESPONSE FACTOR 6 (ARF6) and ARF8 regulate this complex process by promoting petal expansion, stamen filament elongation, anther dehiscence, and gynoecium maturation, thereby ensuring that pollen released from the anthers is deposited on the stigma of a receptive gynoecium. ARF6 and ARF8 induce jasmonate production, which in turn triggers expression of MYB21 and MYB24, encoding R2R3 MYB transcription factors that promote petal and stamen growth. To understand the dynamics of this flower maturation regulatory network, we have characterized morphological, chemical, and global gene expression phenotypes of arf, myb, and jasmonate pathway mutant flowers. We found that MYB21 and MYB24 promoted not only petal and stamen development but also gynoecium growth. As well as regulating reproductive competence, both the ARF and MYB factors promoted nectary development or function and volatile sesquiterpene production, which may attract insect pollinators and/or repel pathogens. Mutants lacking jasmonate synthesis or response had decreased MYB21 expression and stamen and petal growth at the stage when flowers normally open, but had increased MYB21 expression in petals of older flowers, resulting in renewed and persistent petal expansion at later stages. Both auxin response and jasmonate synthesis promoted positive feedbacks that may ensure rapid petal and stamen growth as flowers open. MYB21 also fed back negatively on expression of jasmonate biosynthesis pathway genes to decrease flower jasmonate level, which correlated with termination of growth after flowers have opened. These dynamic feedbacks may promote timely, coordinated, and transient growth of flower organs.
对于自花授粉植物来说，要繁殖，雌雄器官的发育必须在花朵成熟时协调。拟南芥转录因子生长素响应因子 6（ARF6）和 ARF8 通过促进花瓣扩张、雄蕊花丝伸长、花药开裂和雌蕊成熟来调节这个复杂的过程，从而确保从花药释放的花粉沉积在接受性雌蕊的柱头上。ARF6 和 ARF8 诱导茉莉酸的产生，反过来又触发编码 R2R3 MYB 转录因子的 MYB21 和 MYB24 的表达，这些转录因子促进花瓣和雄蕊的生长。为了了解这个花成熟调控网络的动态，我们对 arf、myb 和茉莉酸途径突变体花的形态、化学和全局基因表达表型进行了表征。我们发现 MYB21 和 MYB24 不仅促进了花瓣和雄蕊的发育，还促进了雌蕊的生长。ARF 和 MYB 因子不仅调节生殖能力，还促进了蜜腺的发育或功能以及挥发性倍半萜的产生，这可能吸引昆虫传粉者和/或排斥病原体。缺乏茉莉酸合成或反应的突变体在花正常开放时，花瓣和雄蕊的生长减少，但在较老的花的花瓣中，MYB21 的表达增加，导致后期阶段花瓣的重新和持续扩张。生长素反应和茉莉酸合成都促进了正反馈，这可能确保花开放时花瓣和雄蕊的快速生长。MYB21 也对茉莉酸生物合成途径基因的表达产生负反馈，降低花中的茉莉酸水平，这与花开放后生长的终止相关。这些动态反馈可能促进花器官的及时、协调和短暂生长。
