Molecular characterization of a novel senescence-associated gene SPA15 induced during leaf senescence in sweet potato.

The structure and expression of a novel senescence-associated gene (SPA15) of sweet potato were characterized. The protein coding region of the gene consists of 13 exons encoding 420 amino acids. Apparent homologues of this sweet potato gene are found in a variety of dicot and monocot plants, but not in animals or microorganisms. Examination of the expression patterns of the SPA15 gene in sweet potato reveals that the transcripts of SPA15 are specifically induced in the senescing leaves, and the temporal profile of SPA15 protein accumulation is correlated with that of SPA15 transcripts. Studies on the distribution of SPA15 homologue in rice plants also indicate that SPA15 homologue is up-regulated specifically in senescing rice leaves. Treatment of detached sweet potato leaves with phytohormones including ethylene, methyl jasmonate, salicylic acid and abscisic acid resulted in a high-level induction of SPA15. Immunoelectron microscopic analysis demonstrates that SPA15 is specifically associated with the cell wall. The potential role for SPA15 during leaf senescence is discussed.