Leaf senescence and starvation-induced chlorosis are accelerated by the disruption of an Arabidopsis autophagy gene.
Autophagy is an intracellular process for vacuolar bulk degradation of cytoplasmic components. The molecular machinery responsible for yeast and mammalian autophagy has recently begun to be elucidated at the cellular level, but the role that autophagy plays at the organismal level has yet to be determined. In this study, a genome-wide search revealed significant conservation between yeast and plant autophagy genes. Twenty-five plant genes that are homologous to 12 yeast genes essential for autophagy were discovered. We identified an Arabidopsis mutant carrying a T-DNA insertion within AtAPG9, which is the only ortholog of yeast Apg9 in Arabidopsis (atapg9-1). AtAPG9 is transcribed in every wild-type organ tested but not in the atapg9-1 mutant. Under nitrogen or carbon-starvation conditions, chlorosis was observed earlier in atapg9-1 cotyledons and rosette leaves compared with wild-type plants. Furthermore, atapg9-1 exhibited a reduction in seed set when nitrogen starved. Even under nutrient growth conditions, bolting and natural leaf senescence were accelerated in atapg9-1 plants. Senescence-associated genes SEN1 and YSL4 were up-regulated in atapg9-1 before induction of senescence, unlike in wild type. All of these phenotypes were complemented by the expression of wild-type AtAPG9 in atapg9-1 plants. These results imply that autophagy is required for maintenance of the cellular viability under nutrient-limited conditions and for efficient nutrient use as a whole plant.
Department of Cell Biology, National Institute for Basic Biology, Nishigonaka 38, Myodaiji-cho, Okazaki 444-8585, Japan.
Hideki
H
Hanaoka
Takeshi
T
Noda
Yumiko
Y
Shirano
Tomohiko
T
Kato
Hiroaki
H
Hayashi
Daisuke
D
Shibata
Satoshi
S
Tabata
Yoshinori
Y
Ohsumi
D000595:Amino Acid Sequence; D017209:Apoptosis / Q000235:genetics; D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics*; D000071183:Autophagy-Related Proteins; D002244:Carbon / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D012639:Seeds / Q000254:growth & development; D017386:Sequence Homology, Amino Acid; D014617:Vacuoles / Q000378:metabolism
C466979:APG9 protein, Arabidopsis; D029681:Arabidopsis Proteins; D000071183:Autophagy-Related Proteins; D008565:Membrane Proteins; D002734:Chlorophyll; D002244:Carbon; D009584:Nitrogen