It has long been established that premature leaf senescence negatively impacts the yield stability of rice and particularly in hybrid rice. However, the underlying molecular mechanism driving this relationship remains largely unknown.
A team led by Prof. CHU Chengcai of the State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, recently revealed the molecular mechanism of rice leaf senescence.
Leaf senescence is controlled primarily by developmental age, the onset and progression of this process, however, is also influenced by a number of endogenous and external factors. Abscisic acid (ABA) is thought to be one of the phytohormones that promote leaf senescence. During leaf senescence, an up-regulation of genes associated with ABA signaling and a dramatic increase in endogenous ABA levels have been observed in many plants, and exogenously applied ABA also induces the expression of several senescence-associated genes which accelerate leaf senescence. In addition, a variety of biotic and abiotic stresses also elevate ABA levels and activate signaling pathways, finally leading to the senescence. Thus, it seems quite clear that ABA acts as a key positive regulator of leaf senescence. However, to date, both the molecular mechanism driving ABA-mediated leaf senescence and the specificity of ABA signaling in this process remain largely undetermined.
Chu and colleagues made extensive efforts in last decades on the screening of T-DNA population for premature leaf senescence mutants, and more than 250 independent lines with altered senescence phenotypes were identified, one of the gain-of-function rice mutant prematurely senile 1 (ps1-D) exhibits significant earlier leaf senescence. The detailed characterization revealed that PS1/OsNAP is a key component linking ABA and leaf senescence, which fine-tunes ABA biosynthesis and directly targets senescence-associated genes, finally regulating leaf senescence process.
OsNAP was found both to be specifically induced by ABA, and to function upstream of various senescence marker genes encoding chlorophyll degradation, nutrient transporters, and other senescence-associated proteins, their further studies demonstrated that OsNAP is an important link between ABA and leaf senescence. Strikingly, reduced OsNAP expression led to extended grain filling and an improved seed-setting rate, which significantly enhanced the grain yield. Thus, fine-tuning OsNAP should be a potential means of improving rice yield.
"Differed from animal or human ageing, plant senescence has a strong adaptive advantage since it plays important role in recycling the nutrients from vegetative tissues to reproductive organs, which finally lead to increased reproductive success. In practice, at least 1% of crop yield increase could be achieved by delaying leaf senescence per day. Therefore, dissecting the regulatory components of leaf senescence is not only helpful for the better understanding of this developmental event, but also of significance for genetic manipulation of crop yield." says Dr. LIANG Chengzhen, the first author of this paper.
"Most interestingly, the expression of OsNAP was tightly linked with the onset of leaf senescence in an age-dependent manner, therefore, OsNAP could be an ideal natural senescence onset marker. On the other side, our work, from biotechnological point of view, provides a useful strategy for improving rice yield in the future." Dr. LIANG added.
This study was online published in PNAS (doi: 10.1073/pnas.1321568111) in June 20, 2014. The research was supported by grants from Ministry of Agriculture of China, Chinese Academy of Sciences, and National Natural Science Foundation of China.
AUTHOR CONTACT:
Chengcai Chu, Ph.D.
Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China.
References
Liang C, Wang Y, Zhu Y, Tang J, Hu B, Liu L, Ou S, Wu H, Sun X, Chu J, Chu C (2014) OsNAP connects abscisic acid and leaf senescence by fune-tuning abscisic acid biosynthesis and directly targeting senescence-associated genes in rice. PNAS. Doi: 10.1073/pnas.1321568111.
Figure. Proposed model for OsNAP’s function in rice leaf senescence. (Image by IGDB)
