Senior bureaucrat Girija Vaidhyanathan has replaced Mr Rao.
Here are 10 significant points to know:
- Late Jayalalithaa had picked Rama Mohana Rao, after superseding 17 other senior IAS officers to make him chief secretary. Dr Girija Vaidyanathan is 1981 batch officer. She has 2.5 years of service left before retirement. She held the post of health secretary during 2011-2012 and has also been commissioner of land reforms.
- P. Rama Mohana Rao became the first such officer in the country to face income-tax searches, which soon assumed a political colour.
- In another first, the tax sleuths searched his chamber in the state secretariat, apart from his residence. The operation unfolded on 10 other premises linked to Rao, including the home and offices of his son Vivek.
- Tax officials claimed to have seized currency notes during the searches but no official statement was issued till this evening.
- Agitated AIADMK cadres gathered outside Rao's three-storey bungalow in Anna Nagar and thrashed an Aam Aadmi Party volunteer who chanted slogans against alleged corruption in the state administration. This prompted the tax officials to call the CRPF.
- An AIADMK leader said the tax swoop appeared to be a signal from the Centre to the new government in Tamil Nadu "to behave and cooperate" following Jayalalithaa's death.
- Sources suggested the leads that led the tax investigators to the chief secretary's premises emerged from the CBI's questioning of J. Shekhar Reddy, a building contractor and AIADMK member whom the agency arrested today.
- When chief minister O. Panneerselvam was public works minister, Reddy had bagged the largest volume of state government contracts.
- Tax officials had earlier claimed - after raiding Reddy's home and office two weeks ago and without making public any documentary evidence - that they had seized papers showing huge business transactions between Rao's son and Reddy's companies.
- Rao, who had also served in Gujarat for two years, was credited with tapping the huge revenue potential of sand mining when he was collector of Kancheepuram district near Chennai in 1991-92. It's through this that he is believed to have befriended Reddy.
I-T officials had commenced searches at over a dozen locations in Tamil Nadu and Andhra Pradesh in connection with their tax evasion probe against Rao's son and few other relatives.
The official residence of the Chief Secretary here is also understood to have been brought under the said operation.
The searches, officials said, were related to the department's probe in the�biggest haul of cash and gold here post demonetisation, in which over Rs 142 crore unaccounted assets have been recovered so far.
The total seizure in the case is over Rs 170 crore in a single case related to action against sand mining operators and few others in the state, including S Reddy who was also on the panel of a religious shrine body.
The Enforcement Directorate has also registered a money laundering complaint in this case after the tax department shared official documents with the agency.
(With information from PTI and Telegraph, Calcutta)