On The Cover Crystal structure of GUN4 in complex with a porphyrin molecule. GUN4 is shown in cartoon representation with a transparent surface, while porphyrin is depicted as ball-and-stick in green. The routes of porphyrin delivery are depicted as brown arrows. ChlH is the catalytic subunit of magnesium chelatase, and ChlM is the magnesium protoporphyrin IX O-methyltransferase. Image By: Xuemin Chen.
PLANT PHYSIOLOGY：重庆大学揭示一个整合ABA和BR信号途径的转录因子
理想的植物株型以及对干旱胁迫的耐受性对于提高水稻产量极为重要。本研究作者发现一个水稻中响应逆境的NAC家族的转录因子OsNAC016参与了BR介导的植物株型形成过程以及ABA介导的对干旱胁迫耐受性的调控过程。
首先突变体osnac016的叶片呈现直立状态以及节间变短的表型，而过表达株系则恰恰相反。
研究显示，OsNAC016可以直接结合到BR合成基因D2的启动子上来调控它的表达。而在蛋白水平上，OsNAC016可以与BR信号途径中的负调控子GSK2发生相互作用。作者发现突变体osnac016突变体对干旱胁迫的耐受性显著提高，该突变体失水能力显著下降，这与该突变体气孔对ABA的响应能力提高有关，而过表达株系的表型恰恰相反。
作者发现，在蛋白水平上OSMOTIC STRESS/ABA-ACTIVATED PROTEIN KINASE8 (SAPK8) 可以磷酸化OsNAC016导致其稳定性显著下降。
而且OsNAC016还通过与PLANT U-BOX PROTEIN43 (OsPUB43)发生相互作用导致其自身被ubiquitin/26S proteasome system降解。
从转录组分析证实，OsNAC016促进BR相关基因表达并抑制ABA相关基因表达。
本研究证实OsNAC016是BR介导的株型建成的正调控子，同时也是ABA介导的对干旱胁迫耐受性的负调控子。
Figure 7. A proposed working model for OsNAC016 in BR-regulated plant architecture and ABA-mediated drought response. OsNAC016 promotes plant growth but inhibits drought response. Under normal conditions, BRs repress GSK2 activity, which releases and stabilizes OsNAC016. OsNAC016 positively regulates the expression of BR responsive genes at the mRNA level by binding to the BRRE sites, resulting in promoting BR-regulated plant growth; meanwhile, OsNAC016 inhibits drought responses by repressing ABA/drought responsive genes (left). Under drought stress condition, ABA is produced and activates SAPK8, which results in OsNAC016 phosphorylation. Phosphorylated OsNAC016 facilitates its ubiquitination by interacting with ubiquitin E3 Ligase OsPUB43, and therefore is destabilized, which leads to repression of growth-related genes and alleviation of the OsNAC016 inhibitory effect on drought-related genes, resulting in reduced growth and increased drought tolerance (right).
原文：OsNAC016 regulates plant architecture and drought tolerance by interacting with the
kinases GSK2 and SAPK8
