Minisymposium 7: Protein turnover

Abs # 17001: The Arabidopsis stress-inducible gene AtHVA22d is an autophagy suppressor

Presenter:	Ho, Tuan-Hua David, tho@sinica.edu.tw
Authors	Ho, Tuan-Hua David (A) (B)  Chen, Ching-Nen  (A)
Affiliations:	(A): Washington University in St. Louis (B): Academia Sinica, Taipei

HVA22 is a gene whose expression is highly induced by environmental stress and ABA in barley. Its homologs were found in diverse eukaryotes but not prokaryotes. The yeast (Saccharomyces cerevisiae) homolog is also stress inducible. However, knocking out the yeast HVA22 gene has little effect on the growth of yeast under stress. Following a yeast synthetic mutant screen we have revealed that the function of yeast HVA22 is likely related to vesicular traffic (Brands and Ho, Plant Physiol [2002] 130:1121-1131). Five HVA22 homologs were identified in Arabidopsis, named AtHVA22a-e. Expression of four of the five genes, except AtHVA22c, was enhanced by stress and ABA in vegetative tissues. Among the four genes, AtHVA22d was the most highly induced. Except AtHVA22e, AtHVA22a-d were expressed at the highest level in flowers and flower buds under normal conditions or drought stress compared with that in other tissues. RNA-interference (RNAi) approach was taken to study the function of this gene family. After transformation 194 T1 AtHVA22d RNAi transgenics Arabidopsis were selected. Among which, sixteen lines produced smaller siliques with fewer seeds compared to the control. Some of the sixteen T1 lines were backcrossed in addition to self-pollination to generate backcross (bc) F1 and T2 plants. Three of the T2 and one bc F2 lines showed stable phenotype. The phenotype was co-segregated with the RNAi transgene at T2, bc F2, and T3 populations. The cause of seed reduction is multiple, which are short filaments, collapsed or non-viable pollen, and defective carpel. Very active autophagy was found in the filament cells as evidenced by the presence of partially degraded organelles in vacuoles. We suggest that AtHVA22d is likely an autophagy suppressor that is needed to prevent premature cell destruction process when plant tissues are under stress.