Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.
Purdue University Center for Plant Biology, Purdue University, West Lafayette, IN, 47907, USA.
Plant J. 2019 Jun;98(5):898-911. doi: 10.1111/tpj.14289. Epub 2019 Mar 27.
Hypocotyl growth during seedling emergence is a crucial developmental transition influenced by light and phytohormones such as ethylene. Ethylene and light antagonistically control hypocotyl growth in either continuous light or darkness. However, how ethylene and light regulate hypocotyl growth, including seedling emergence, during the dark-to-light transition remains elusive. Here, we show that ethylene and light cooperatively stimulate a transient increase in hypocotyl growth during the dark-to-light transition via the light-mediated stabilization of 1-aminocyclopropane-1-carboxylic acid (ACC) synthases (ACSs), the rate-limiting enzymes in ethylene biosynthesis. We found that, in contrast to the known inhibitory role of light in hypocotyl growth, light treatment transiently increases hypocotyl growth in wild-type etiolated seedlings. Moreover, ACC, the direct precursor of ethylene, accentuates the effects of light on hypocotyl elongation during the dark-to-light transition. We determined that light leads to the transient elongation of hypocotyls by stabilizing the ACS5 protein during the dark-to-light transition. Furthermore, biochemical analysis of an ACS5 mutant protein bearing an alteration in the C-terminus indicated that light stabilizes ACS5 by inhibiting the degradation mechanism that acts through the C-terminus of ACS5. Our study reveals that plants regulate hypocotyl elongation during seedling establishment by coordinating light-induced ethylene biosynthesis at the post-translational level. Moreover, the stimulatory role of light on hypocotyl growth during the dark-to-light transition provides additional insights into the known inhibitory role of light in hypocotyl development.
下胚轴在幼苗出土过程中的生长是一个关键的发育转变，受到光和植物激素（如乙烯）的影响。乙烯和光在连续光照或黑暗中拮抗地控制下胚轴的生长。然而，乙烯和光如何在黑暗到光照的转变过程中调节下胚轴的生长，包括幼苗出土，仍然难以捉摸。在这里，我们表明，乙烯和光通过光介导的 1-氨基环丙烷-1-羧酸（ACC）合酶（ACS）的稳定来协同刺激黑暗到光照转变过程中瞬时增加下胚轴的生长，ACS 是乙烯生物合成的限速酶。我们发现，与光对下胚轴生长的已知抑制作用相反，光处理在野生型黄化幼苗中瞬时增加了下胚轴的生长。此外，ACC，乙烯的直接前体，强调了 ACC 在黑暗到光照转变过程中对下胚轴伸长的影响。我们确定，光通过在黑暗到光照转变过程中稳定 ACS5 蛋白导致下胚轴的瞬时伸长。此外，对 C 末端发生改变的 ACS5 突变蛋白的生化分析表明，光通过抑制通过 ACS5 的 C 末端起作用的降解机制来稳定 ACS5。我们的研究表明，植物通过协调光照诱导的乙烯生物合成在翻译后水平上调节幼苗建立期间的下胚轴伸长。此外，光在下胚轴生长中的刺激作用在黑暗到光照的转变过程中提供了对光在下胚轴发育中的已知抑制作用的额外见解。
